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This study explored the three-dimensional flow characteristics in a recirculation zone near a permeable buttress in curved channels with varying curvatures. Understanding these characteristics is crucial for managing natural river bends, as rivers often meander, with backwater zones formed behind obstructions, such as mountains in the riverbed. The direct comparison of the recirculation zones across different bend types revealed the correlation between the flow characteristics and bend curvature. However, previous studies have focused on flow velocities and turbulent kinetic energy without a probability density analysis. This analysis provided a more comprehensive understanding of the flow characteristics. Gaussian kernel density estimation was applied in this study to observe the distribution of the flow velocities, turbulent kinetic energy, and turbulent kinetic energy dissipation rate. The results indicated that the longitudinal time-averaged flow velocity in the recirculation zone typically ranged from −0.2 m/s to −0.8 m/s, with all the skewness coefficients exceeding 0. The horizontal time-averaged flow velocity in the recirculation zone fell between −0.175 m/s and −0.1 m/s. The skewness coefficients were negative at water depths of 16%, 33%, and 50% within the 90° and 180° bends, indicating a non-normal distribution. The probability density distribution of turbulent kinetic energy in the recirculation zone was skewed, ranging from 0 to 0.02 m2·s−2, with the skewness coefficient almost always greater than 0. The plot demonstrated multiple peaks, indicating a broad distribution of turbulent kinetic energy rather than a concentration within a specific interval. This distribution included both the high and low regions of turbulent kinetic energy. Although the overall rate of turbulent kinetic energy dissipation in the recirculation zone was relatively low, there were multiple peaks, suggesting the localized areas with higher dissipation rates alongside the regions with lower rates. These findings were significant for managing the meandering river channels, restoring the subaqueous ecosystems, understanding the pollutant diffusion mechanisms in backwater areas, the sedimentation of nutrient-laden sediments, and optimizing the parameters for spur dike design. [ABSTRACT FROM AUTHOR]

The mean slope flow velocity is critical in soil erosion models but the mechanism of its variation under rigid vegetation cover remains unclear. On natural slopes, vegetation grows predominantly perpendicular to the horizontal plane (BH), with some growing perpendicularly to the slope surface (BS); however, current research often neglects the effects of these two growth directions on the mean flow velocity. We conducted simulation experiments using different coverage levels, rigid vegetation, slope angles, and flow rates and showed that the flow rate and slope significantly influenced the mean flow velocity. As the coverage of rigid vegetation increased, the mean flow velocity increased more under conditions perpendicular to the horizontal plane (BH) and those perpendicular to the slope (BS). A model for predicting mean flow velocity was developed using vegetation equivalent roughness and the Manning formula, which accurately predicted flow velocity in different conditions. This study contributes to the refinement of slope flow theory and provides data that support soil and water conservation efforts. [ABSTRACT FROM AUTHOR]

Preparative regimens before Hematopoietic Cell Transplantation (HCT) damage the bone marrow (BM) microenvironment, potentially leading to secondary morbidity and even mortality. The precise effects of cytotoxic preconditioning on bone and BM remodeling, regeneration, and subsequent hematopoietic recovery over time remain unclear. Moreover, the influence of recipient age and cytotoxic dose have not been fully described. In this study, we longitudinally investigated bone and BM remodeling after busulfan treatment with low intensity (LI) and high intensity (HI) regimens as a function of animal age. As expected, higher donor chimerism was observed in young mice in both LI and HI regimens compared to adult mice. Noticeably in adult mice, significant engraftment was only observed in the HI group. The integrity of the blood-bone marrow barrier in calvarial BM blood vessels was lost after busulfan treatment in the young mice and remained altered even 6 weeks after HCT. In adult mice, the severity of vascular leakage appeared to be dose-dependent, being more pronounced in HI compared to LI recipients. Interestingly, no noticeable change in blood flow velocity was observed following busulfan treatment. Ex vivo imaging of the long bones revealed a reduction in the frequency and an increase in the diameter and density of the blood vessels shortly after treatment, a phenomenon that largely recovered in young mice but persisted in older mice after 6 weeks. Furthermore, analysis of bone remodeling indicated a significant alteration in bone turnover at 6 weeks compared to earlier timepoints in both young and adult mice. Overall, our results reveal new aspects of bone and BM remodeling, as well as hematopoietic recovery, which is dependent on the cytotoxic dose and recipient age. [ABSTRACT FROM AUTHOR]

This study aims to address the issue of high energy consumption in the hydrocyclone separation process. By introducing a novel slotted overflow pipe structure and utilizing experimental and response surface optimization methods, the optimal parameters were determined. The research results indicate that the number of slots, slot angles, and positioning dimensions significantly influence the performance of the hydrocyclone separator. The optimal combination was found to be three layers of slots, a positioning dimension of 5.3 mm, and a slot angle of 58°. In a Φ100mm hydrocyclone separator, validated through multiple experiments, the separation efficiency increased by 0.26% and the pressure drop reduced by 24.88% under a flow rate of 900 ml/s. CFD simulation verified the reduction in internal flow field velocity and pressure drop due to the slotted structure. Therefore, this study provides an effective reference for designing efficient and low-energy hydrocyclone separators. [ABSTRACT FROM AUTHOR]

AbstractErosion wear presents a significant challenge in the operation of hydrodynamic systems, particularly in centrifugal pumps. To address this issue, this study employs the coarse-grained Discrete Element Method (CGDEM) coupled with Computational Fluid Dynamics (CFD) to predict erosion wear areas and elucidate particle behavior dynamics. The simulation considers spherical solid particles (brown corundum) with diameters ranging from 0.3 mm to 1 mm and volume fractions of 15% and 5%. The flow field is calculated using the Navier-Stokes equations and the shear-stress-transport (SST) k-ω model. Particle movement is tracked using Newton’s second law, considering drag and gravitational forces. Results indicate that the highest turbulent kinetic energy (TKE) occurs at a flow rate of Q = 15 m3/h. Moreover, the pressure reduces slightly when the flow rate increases, although flow velocity might increase with volumetric discharge. Additionally, increased particle diameter leads to greater erosion wear, particularly on blade leading edges, the volute tongue area, and the volute casing belly region. As particle mass concentration intensifies, wear rates on the volute wall and inner hub edge also increase. The study’s robustness is demonstrated through alignment between experimental and numerical data. This investigation offers valuable insights into erosion dynamics in centrifugal pumps, crucial for enhancing operational efficiency and mitigating erosion-induced challenges in these critical systems. [ABSTRACT FROM AUTHOR]

As building becomes more leak-tight, air refreshment to improve indoor air quality is needed for healthy living standards. In the quest to ensure comfortable indoor climatic conditions, energy recovery ventilators (ERV) are used to provide air refreshment and thermal comfort. In this study, a fixed plate air-to-air ERV was analysed to determine its effectivity in terms of energy recovery during air refreshment. A customized test bench was built and used to acquire the instantaneous surface temperatures of the heat exchanger plates contained in the ERV during air refreshment. Also, a numerical model of the ERV was developed and validated by comparing its output from simulation with experiment results under the same conditions. The model consisted of a single heat exchanger plate and the air across the plate surface. To capture the effect of heat transfer between the air and the heat exchanger plate in 3D, the model was discretized into numerous cells. From the experiment and simulation results, the air-to-air ERVs were more effective in recovering thermal energy at low flow velocity than at high flow velocity. At lower flow velocity, it will take a longer time duration before any significant impact is made on the thermal conditions of the building, comparatively. The prediction of the model was within acceptable margins and could be used to provide insight on the ERVs performance improvement. [ABSTRACT FROM AUTHOR]

Large-mouth bass originally lived in rivers and lakes and now is often raised in recirculating aquaculture systems (RAS). However, the shortcoming of RAS is that there is very limited space for swimming fish in a high-density culture environment, thus leading to a lack of exercise. To investigate the effects of exercise training on growth performance, digestive enzymes, stress, and antioxidant capacity of large-mouth bass in a RAS, three training water flow velocities with three replicates were used in the present study: low water velocity: 0.5 body length per second (bl/s) (LV); medium water velocity: 1 bl/s (MV); and high water velocity: 1.5 bl/s (HV). 270 large-mouth bass (average initial body weight 47.51 ± 1.44 g, initial body length 12.71 ± 0.06 cm) were randomly divided into nine tanks (30 fish per tank). After 27 days experiment, the results showed that the growth performance of large-mouth bass, including feed intake, weight gain rate, and specific growth rate, in the HV group was significantly higher compared to the other groups. On the physiological level, the lipase and amylase activities were significantly increased in the HV group compared to the other groups. For the stress response parameters, the cortisol, glucose and lactate concentrations in the HV group were significantly increased, which may indicate higher stress in the HV group. Regarding the antioxidant enzyme activities, the activities of catalase (CAT) and glutathione peroxidase (GSH-PX) in the LV group were significantly higher than those in the HV group, which indicated that fish suffered higher oxidative stress in the LV group. Regarding the immune-related parameters, LZM and ACP activities had no significant differences among the groups, while AKP activities in the MV and HV groups were significantly higher than that in the LV group. Overall, the results demonstrated that exercise training had significant effects on the growth, digestion, stress, and immune response of large-mouth bass. It is suggested that exercise training with 1.5 bl/s can enhance fish growth, however, it also presents a potential risk of inducing stress in fish. Therefore, in rearing largemouth bass in RAS, the setting of water flow velocity should not only focus on the growth of large-mouth bass but also consider its welfare. [ABSTRACT FROM AUTHOR]

Natural gas is transported from production areas using high-pressure pipelines to pass through pressure reducing stations and then to the consumer. When temperatures drop, the problem of freezing of natural gas and ice appears. To protect against this phenomenon, we use a water bath to improve the temperature of the gas before reducing its pressure. One of the essential elements in the design of a low thermal efficiency water bath heater is the gas coil that runs inside the heater. In this study, the analysis of heat transfers and gas flow velocity inside the corrugated coil was performed with varying wave amplitude (10 mm, 15 mm, and 20 mm). The three-dimensional unsteady Reynolds-Navier-Stokes equations are solved using both the realizable k-ε turbulent model and the finite volume method to obtain the flow field. The results of this study showed that using corrugated coils with a larger capacity leads to an increase in the Nusselt number and friction factor, respectively, by about 6.57% and 114%. In general, the heat exchange inside the corrugated twisted gas coil can be enhanced by increasing the wave amplitude. [ABSTRACT FROM AUTHOR]

In the present work, the impact of periodic body acceleration on the unsteady flow of blood in an inclined artery has been investigated. The blood is represented by an incompressible, viscous, non-Newtonian Jeffrey fluid. The artery is assumed to have mild overlapping stenoses inside its lumen. The perturbation method is used to solve the governing nonlinear coupled partial differential equations. Here, the Womersley frequency parameter is considered small enough for blood flow through arteries. Analytic expressions for the wall shear stress, stress at the critical height of stenosis, velocity profile, volumetric flow rate, pressure drop, resistive impedance, and effective viscosity are obtained using the perturbation technique. Regarding different flow parameters, the effects of body acceleration, pulsatility, the non-Newtonian character of blood, and velocity slip are examined and graphically depicted. It is concluded from the present analysis that the flow impedance rises when the stenosis reaches its critical height, but it falls as the velocity slip at the wall increases. It is also observed that when body acceleration increases, flow rate, velocity, and shear stress near the critical height of stenosis all rise, whereas wall shear stress decreases as body acceleration rises. Here, we also analyzed the flow pattern of the non-Newtonian Jeffrey fluid when it passes through the overlapped stenosed artery with the help of streamlines. The results of the present problem have been verified with the previous existing results in the literature. [ABSTRACT FROM AUTHOR]

The present article deals with the modulation of electroosmotic flow (EOF) and transport of ionic species within soft nanochannels. The power-law model is adopted to consider the non-Newtonian nature of bulk electrolyte. The soft layer grafted along the rigid walls often bears ionizable functional groups, which in turn leads to the net volumetric charge. Besides, the dielectric permittivity of the soft layer is in general lower than that of the ambient electrolyte solution, which in turn leads to ion partitioning effect. The net volumetric charge within the soft polymeric layer coated along the channel walls may be moderate to large. For such a case, the ion steric effect may play a pivotal role on the modulation of electrostatic potential and thereby the flow field across the channel. In the present article, we aim to study the flow modulation across the soft nanochannels considering all such intrinsic effects. The mathematical model is based on modified Poisson−Boltzmann equations based on Carnahan−Striling model, Cauchy momentum equation for flow field. The governing equations are solved via a suitable numerical scheme based on finite difference method to calculate the electrostatic potential as well as flow velocity. We further analyze the impact of pertinent parameters on the flow modulation and ion selectivity parameter. [ABSTRACT FROM AUTHOR]

Peritonitis is a common and life-threatening inflammatory disease. Myeloid cells are elevated in the peripheral blood and contribute to peritonitis, but their circulating dynamics are not clear. In vivo flow cytometry (IVFC) is a noninvasive technique for monitoring the dynamics of circulating cells in live animals. It has been extensively used to detect circulating tumor cells, but rarely for monitoring immune cells. Here, we describe a method adapting an intravital microscope for IVFC so that we can monitor LysM-EGFP-labeled circulating myeloid cells in a tumor necrosis factor (TNF) α-induced peritonitis mouse model. Using this IVFC method, we quantified the blood flow velocity and cell concentration in circulation. We observed a significant increase in LysM-EGFP+ cells in circulation after TNFα intraperitoneal (i.p.) injection, which reached a plateau in ~20 min. Conventional cytometry analysis showed that most LysM-EGFP+ cells were neutrophils. Increasing blood neutrophils were accompanied by neutrophil recruitment to the peritoneal cavity and neutrophil emigration from the bone marrow. We then monitored neutrophil CD64 expression in vivo and found a significant increase in TNFα-induced peritonitis. We also found that CD18 blockade doubled the circulating neutrophil number in TNFα-induced peritonitis, suggesting that CD18 is critical for neutrophil recruitment in peritonitis. Overall, we demonstrate that IVFC techniques are useful for studying the circulating dynamics of immune cells during inflammatory diseases. [ABSTRACT FROM AUTHOR]

The influence of design parameters on the thermal performance of a packed bed thermocline thermal energy storage (TES) system was analyzed. Both one-dimensional (1D) and two-dimensional (2D) in-house codes were developed in MATLAB environment. The diameter of solid filler, height of storage tank, and fluid velocity were varied. The thermal performance of the system, such as discharging time, thermocline thickness, and energy efficiency was calculated. As the diameter of the solid filler and fluid velocity increased, and the height of the storage tank decreased, the discharging time decreased. As the diameter of the solid filler and the height of storage tank increased, the thermocline generally became thicker. The thermocline thickness according to the fluid velocity showed non-monotonic behavior: initially increasing and then decreasing, since it affected heat transfer coefficient, fluid-solid contact time and discharging time, which affected thermocline expansion. The 2D model exhibited higher energy efficiency than the 1D model, due to the consideration of the additional wall heating to the fluid, resulting in extended discharging time except for very low flow velocities. [ABSTRACT FROM AUTHOR]

Most wet-type multi-path ultrasonic flowmeters have their measurement accuracy rate deteriorate as the flow rate is decreased. Curve-fitting on the characteristics of ultrasonic flowmeters is essential to improve their measurement accuracy rate. This hinders their use as transfer standards in inter-laboratory comparisons for water flow metrology. A breakthrough to enhance the measurement accuracy rate of ultrasonic flowmeters is needed. This study suggests that the concept of near-wall flow velocity should enhance the characteristics of ultrasonic flowmeters. As a result, repeatability can be improved as low as ±0.02 %, which should be suitable to be used as transfer standards. Two main points of using the near-wall flow velocity for ultrasonic flowmeters are emphasized. One is a formula to describe the near-wall flow velocity as a function of both Reynolds number and surface roughness. The other is the results of comparison calibrations between two national metrology institutes, which can support measurement equivalence. In particular, the number of equivalence is less than one (∣En∣ ≤ 1), and the inconclusiveness parameter is less than two (ucomp/ubase ≤ 2) if the near-wall flow velocity is applied for ultrasonic flowmeters. This implies that the ultrasonic flowmeters could be used as transfer standards for the forthcoming inter-laboratory comparisons. [ABSTRACT FROM AUTHOR]

Background: Clinical trials demonstrating improved cardiovascular outcomes with SGLT2 inhibitors have often had limited representation from Black and Hispanic populations. While the mechanisms of action are not well known, ethnicity- or gender-based receptor physiology may render SGLT2 inhibitors a better agent in certain populations over others. Methods: A medical records query yielded diabetic patients initiated on SGLT2 inhibitors between 2013 and 2020. Patients with coronary artery disease, cardiac arrhythmias, and heart failure were excluded. Transthoracic echocardiographic studies (TTE) before and after starting SGLT2 inhibitors were analyzed, and post-processing left ventricular global longitudinal strain (LV GLS) analysis was also performed on each echocardiographic study. Univariate outliers and patients with missing data were excluded. Results: Among 94 patients with TTE (mean age 60.7 years; 68% Hispanics, 22.3% Blacks; median follow up of 7 months), there were significant improvements in the mean LV GLS (−15.3 vs. −16.5; p = 0.01), LV mass (LVM) (198.4 ± 59.6 g vs. 187.05 ± 50.6 g; p = 0.04), and LV mass index (LVMI) (100.6 ± 26.6 g/m2 vs. 94.3 ± 25.4 g/m2; p = 0.03) before and after initiating SGLT2 inhibitors but no significant change in the ratio (MV E/E') of peak early diastolic mitral flow velocity (E) and spectral pulsed-wave Doppler-derived early diastolic velocity from the septal mitral annulus (E') (12.5 ± 5.7 vs. 12.7 ± 4.8; p = 0.38). Changes in HbA1c (r2 = 0.82; p = 0.026), LVM (r2 = 0.20; p = 0.04), and LVMI (r2 = 0.20; p = 0.04) were found to be independently associated with changes in values of LV GLS on follow-up echocardiograms, when compared to the pre-medication LV GLS number. Conclusion: Non-White diabetic patients receiving SGLT2 inhibitors against a backdrop of other cardioprotective medications demonstrate significant improvements in LV remodeling and LV GLS, driven in part by an improvement in glycemic control. Large, prospective studies are needed to explore the differences in the therapeutic actions of SGLT2 inhibitors among different populations. [ABSTRACT FROM AUTHOR]

The significant rainfall in October 2018 in northern Iran caused devastating flooding that caused considerable economic losses and claimed at least nine lives. Following the flooding, several bridges have suffered different levels of damage. Immediately after the event, the authors conducted a field investigation to study the performance of RC bridges during the flood. This paper presents the failure modes of flood-affected bridges and provides reasons for every failure case. The results revealed that scour around foundations, pier tilting, flexural failure of piers, and superstructure unseating were the most significant failure modes observed. Pile-supported bridges performed notably better than those with shallow foundations. In addition, observations have revealed that structural integrity plays a crucial role in the general stability of bridges during flooding. Pier ductility is another significant parameter that affects the performance of bridges during flood events. Finally, fragility curves were developed based on the empirical data set provided from the post-flood status of the bridges in the affected region. The river flow velocity (Vs), maximum flow discharge (Qp), and Qp normalized to the 10-year average river discharge (Qm) were considered intensity measures of the fragility analysis. The correlation analyses revealed that despite Vs and Qp/Qm , the flow discharge was not an appropriate intensity measure for generating fragility curves. [ABSTRACT FROM AUTHOR]

A heterogeneous condensation process facilitates the growth of fine particulate matter, making it more easily removable. The aim of this study was to effectively eliminate pre-existing fine particles in the atmosphere by investigating the growth characteristics of particles in turbulent water vapor environments using experimental and numerical methods. The results reveal that the presence of soluble and hydrophilic particles in atmospheric fine particulate matter enhances their growth compared to coal particles. Increasing temperature differences, reducing particle number concentrations, and elevating the proportion of soluble particle components contribute to particle growth. When the temperature difference is below 10K, particle growth is less effective. The beneficial impact of particle collision and coagulation, partly offsetting water vapor competition, was observed with an increase in particle number concentration. The addition of soluble and hydrophilic components promoted particle activation, further fostering particle growth. The region near the wall exhibited more significant particle growth due to higher supersaturation and lower flow velocity. These findings theoretically support the application of heterogeneous condensation processes in atmospheric purification. [ABSTRACT FROM AUTHOR]

Debris flow mobility can vary during propagation due to changes in flow volume and bulk flow behavior resulting from the absorption of water from runoff. This study aims to investigate the effect of runoff on debris flow propagation by presenting an integrated model that considers the processes of rainfall, vegetation interception, soil infiltration, runoff generation, and debris flow propagation. Specifically, the study adopts an elevation-based empirical formula to evaluate the spatial distribution of rainfall and introduces a parameter for water absorption rate into the depth-averaged two-layer model that is used for describing the dynamics of runoff and debris flow. Through alternative simulations of the 2020 debris flow in the Meilong catchment, the study illustrates the significant effects of water absorption on debris flow propagation. The results indicate that as the water absorption rate of the debris mass increases, debris flow mobility also increases, since more mass and energy are transferred from runoff to debris flow. In addition, the spatial and temporal patterns of rainfall intensity can modify the propagation velocity of debris flow by influencing runoff dynamics. [ABSTRACT FROM AUTHOR]

This paper presents simulations of dam-break flows of Herschel–Bulkley viscoplastic fluids over complex topographies using the shallow water equations (SWE). In particular, this study aims to assess the effects of rheological parameters: power-law index (n), consistency index (K), and yield stress ( τ c ), on flow height and velocity over different topographies. Three practical examples of dam-break flow cases are considered: a dam-break on an inclined flat surface, a dam-break over a non-flat topography, and a dam-break over a wet bed (downstream containing an initial fluid level). The effects of bed slope and depth ratios (the ratio between upstream and downstream fluid levels) on flow behaviour are also analyzed. The numerical results are compared with experimental data from the literature and are found to be in good agreement. Results show that for both dry and wet bed conditions, the fluid front position, peak height, and mean velocity decrease when any of the three rheological parameters are increased. However, based on a parametric sensitivity analysis, the power-law index appears to be the dominant factor in dictating fluid behaviour. Moreover, by increasing the bed slope and/or depth ratio, the wave-frontal position moves further downstream. Furthermore, the presence of an obstacle is observed to cause the formation of an upsurge that moves in the upstream direction, which increases by increasing any of the three rheological parameters. This study is useful for an in-depth understanding of the effects of rheology on catastrophic gravity-driven flows of non-Newtonian fluids (like lava or mud flows) for risk assessment and mitigation. [ABSTRACT FROM AUTHOR]

This study proposes the foremost application of the entropy concept to investigate the streamwise S-type mean velocity distribution with infection-phenomenon in turbulent open-channel flows and turbulent Couette flows. Probability based fractional entropy is used for this study. Using the concept of entropy maximization the velocity distribution models are derived. Proposed models are fully analytical and applicable to the whole flow depth in both for open-channel flows and the turbulent Couette flows. All the proposed models are validated with different experimental data sets, field data and DNS data available in the literature. The validation results show good performance for both of the velocity distribution models. Apart form validation, the present velocity distribution models are compared with deterministic (non-entropy based) models since there exists no entropy based velocity distributions to describe the infection-phenomenon in turbulent open-channel flows and turbulent Couette flows. To understand the performance of these models, the relative error and the coefficient of determination ( R 2 ) are computed. Results of the error analysis show the good efficiency of the proposed models for several experimental and field data sets. [ABSTRACT FROM AUTHOR]

To determine the spray characteristics of internal-mixing gas-liquid injector under various operating conditions, the experimental facilities for spraying are established. By means of high-speed camera, laser particle size analyzer and PIVlab, the effects of gas and liquid flow conditions on the spray characteristics, such as position of jet impingement, spray angle, breakup length, velocity distribution and droplet size, have been investigated in detail. Experimental results demonstrated that there are two types of atomization for this injector, namely impact atomization and aerodynamic atomization. The impingement position of the liquid jets is outside of the injector exit. Alternatively, no impingement occurs between the jets. The spray angle increases with the increase of liquid flow rate, and decreases with the increase of gas flow rate. The breakup length decreases with the increase of the liquid or gas flow rate. The higher the liquid flow rate, the greater the velocity distributed along the axial and radial direction. However, the effect of gas flow rate on the velocity along the axial and radial directions acts differently at different spatial position. An increase in the liquid flow rate causes the droplet diameter to increase first and then decrease. The droplet size will decrease when the gas-liquid momentum ratio increases. • Two types of atomization process: "aerodynamics fragmentation" and "impact fragmentation". • Effects of gas/liquid flow rates on the position of jet impingement, spray angle, breakup length, velocity distribution and droplet size. • Effects of operating conditions on the two atomization mechanisms: "aerodynamics fragmentation" and "impact fragmentation". • The dominant factor (mutual impact between the liquid jets or gas-liquid interaction) in atomization process depends on the gas flow rate. [ABSTRACT FROM AUTHOR]

• Ammonia condensation has been experimentally studied in 8 mm and 11 mm tubes. • A new phenomenological model has been proposed for ammonia condensation. • The lowest condensation HTCs characterise the downstream flow. The paper proposes the experimental study of ammonia condensation in aluminium tubes with 8 mm and 11 mm internal diameters. The new study aimed to compare and extend the existing ammonia in-tube condensation data. The lines were tested mainly in horizontal configuration at mass velocities of 20 to 160 kg·m−2s−1, saturation temperature of 35 to 65 °C and inlet vapour quality of 0.1 to 0.9. Shah (1979), laminar-laminar Dobson and Chato (1998), and Cavallini et al. (2001) models predict well ammonia condensation HTCs at mass velocities of 120 to 160 kg·m−2s−1. A new phenomenological model has been proposed for the mass velocities of 20 to 120 kg·m−2s−1, predicting the test data with an accuracy of ±20 %. Similar ammonia condensation HTCs have been obtained for horizontal and upstream flows at a mass velocity above 120 kg·m−2s−1. The lowest condensation HTCs at the considered boundary conditions characterise the downstream configuration of an in-tube condenser at a mass velocity below 120 kg·m−2s−1. However, inclining the ID 8 mm tube by 15° from the normal substantially increases the condensation HTCs by 10 to 30 %, depending on vapour quality. At the inclinations of 15 to 45° from the horizontal line toward the downstream flow, the condensation HTCs exceed the ones of horizontal flow by 10 to 15 % at the vapour quality of <0.5 and low mass velocity of 80 kg·m−2s−1. [ABSTRACT FROM AUTHOR]

The interaction between the leaf and airflow directly influences droplet deposition on the leaf surface. This paper investigates the effect of this interaction on droplet deposition. A bidirectional fluid-structure coupling model was established using computational fluid dynamics (CFD) based on mechanical parameters and surface roughness of tomato leaves to simulate tomato leaf deposition under air-assisted spraying. Utilizing the model and considering air velocity, droplet size, and initial leaf inclination as experimental factors, a three-factor, three-level central composite design simulation and response surface analysis were conducted to examine the influence of each factor on the surface deposition amount of tomato leaves. The order of influence of each factor on the deposition amount is as follows: a quadratic regression model was established with the flow velocity having the greatest influence, followed by initial leaf inclination and then droplet size. The influence of each factor on the deposition distribution of the leaf surface was compared and studied separately. Airflow velocity significantly affected the deposition distribution of the leaf surface. Higher airflow velocities resulted in a lower proportion of deposition at the tip and a higher proportion at the base. The maximum relative errors of leaf deformation and deposition were 8.77% and 17.44%, respectively. The findings of this research can provide valuable insights for optimizing the working parameters of air-assisted atomizers. [ABSTRACT FROM AUTHOR]

We present the design and laboratory tests for a new Q-band frequency tunable Doppler backscattering (DBS) system suitable for probing poloidal wavenumber kñ = 6–8 cm−1 density fluctuations and their flow velocities in the pedestal and scape-off layer (SOL) of the DIII-D tokamak. This system will provide new measurements in the increasingly important and under-diagnosed far pedestal and SOL plasma regions. These results are important for experimental transport studies and necessary for the validation of transport models, both of which are important to fusion energy research. The use of a single tunable frequency reduces the complexity and potential failure points as compared to a multichannel system. This new system utilizes a 33–50 GHz tunable source and will be integrated into the current V-band DBS in DIII-D using a broadband Q- and V-band multiplexer. A full-scale mockup of the quasi-optical system was used to test and optimize the performance. These tests include beam profile measurements at different distances (and angles) from a paraboloidal focusing and steering mirror. The measurements cover the full frequency range 33–75 GHz of the integrated/combined Q–V band DBS system and target a large radial coverage of the low-field side of the plasma from ρ = 1.1 to ρ = 0.5, where ρ is the normalized flux surface radial coordinate. [ABSTRACT FROM AUTHOR]

On pulsed fusion experiments, the neutron time of flight (nToF) diagnostic provides critical information on the fusion neutron energy spectrum. This work presents an analysis technique that uses two collinear nToF detectors, potentially to measure nuclear bang time and directional flow velocities. Two collinear detectors may be sufficient to disambiguate the contributions of nuclear bang time and directional flow velocities to the first moment of the neutron energy spectrum, providing an independent measurement of nuclear bang time. Preliminary results from measured nToF traces on the National Ignition Facility and additional applications of this technique are presented. [ABSTRACT FROM AUTHOR]

Secondary metabolites produced by fungi are well known for their biological properties, which play important roles in medicine. These metabolites aid in managing infections and treating chronic illnesses, thereby contributing substantially to human health improvement. Despite this extensive knowledge, the vast biodiversity and biosynthetic potential of fungi is still largely unexplored, highlighting the need for further research in natural products. In this review, several secondary metabolites of fungal origin are described, emphasizing novel structures and skeletons. The detection and characterization of these metabolites have been significantly facilitated by advancements in analytical systems, particularly modern hyphenated liquid chromatography/mass spectrometry. These improvements have primarily enhanced sensitivity, resolution, and analysis flow velocity. Since the in vitro production of novel metabolites is often lower than the re-isolation of known metabolites, understanding chromatin-based alterations in fungal gene expression can elucidate potential pathways for discovering new metabolites. Several protocols for inducing metabolite production from different strains are discussed, demonstrating the need for uniformity in experimental procedures to achieve consistent biosynthetic activation. [ABSTRACT FROM AUTHOR]

The hypervapotron structure was considered to be a feasible configuration to meet the high heat-dissipating requirement of divertors in nuclear fusion devices. In this work, symmetric CuCrZr-based transverse microchannels (TMHC) and longitudinal microchannels (LMHC) with an integrated hypervapotron channel were proposed and manufactured, and subcooled flow boiling experiments were conducted using deionized water at an inlet temperature of 20 °C with a traditional flat-type hypervapotron channel (FHC) for comparison. The LMHC and TMHC obtained lower wall temperatures than the FHC for all conditions, and the TMHC yielded the lowest temperatures. The heat transfer coefficients of the LMHC and TMHC outperformed the FHC due to the enlarged heat transfer area, and the TMHC had the greatest heat transfer coefficient (maximumly increased by 132% compared to the FHC) because the transverse-arranged microchannels were conductive, promoting the convection and liquid replenishment ability by introducing branch flow between fins; however, the microchannels of the LMHC were insensible to flow velocities due to the block effect of longitudinal microchannels. The LMHC obtained the largest pressure drop, and the pressure drop for the FHC and TMHC were comparable since the transverse-placed microchannels had little effect on frictional pressure loss. The TMHC attained the greatest comprehensive thermohydraulic performance which might bring significant insight to the structural design of hypervapotron devices. [ABSTRACT FROM AUTHOR]

The attachment of porous media to a blunt trailing edge (TE) can significantly suppress vortex shedding processes and the related tonal noise, yet the near-wall and internal flow fields of porous media are difficult to analyze experimentally and rely on numerical simulations to elucidate the internal flow features. A structured porous trailing edge (SPTE) has been recently designed that follows a methodology of a structured porous coated cylinder. The SPTE acoustic response was compared against randomized porous media with 10 and 30 pores/in. in an anechoic wind tunnel over a range of flow velocities. Acoustic beamforming revealed that the dominant acoustic sources were at the end of the solid plate, even when a porous TE was attached. A region of integration was used to extract acoustic spectra without additional noise sources, revealing that the SPTE possesses superior noise reduction capability. Dipolar directivity patterns were observed at the vortex shedding frequency for each TE, and the coherence between microphones revealed the complex acoustic propagation of the high-frequency content. A wavelet analysis revealed how the SPTE breaks periodic vortex shedding cycles into smaller cycles over a wider frequency range, leading to an overall noise reduction relative to the other TEs. [ABSTRACT FROM AUTHOR]

This study investigated morphological differences, habitat preference, and ecological niche overlap in two sympatric Capoeta species i.e., Capoeta. damascina and Capoeta umbla collected from the Sirvan river drainage. Ten environmental factors, including pH, temperature, electrical conductivity (EC), total dissolved solids (TDS), river width, river depth, flow velocity, altitude, slope, and dissolved oxygen (DO) were measured during sampling time. A total of 17 morphometric characteristics were measured using digital calipers for traditional morphometrics (TM). For the geometric morphometric method (GM), 2D pictures were taken from the left side of the fresh samples, by tpsDig2 software, and 16 landmark points were defined and digitalized to extract body shape data. The data were analyzed using t-test, Mann–Whitney, principal component analysis (PCA), and discriminant function analysis based on the P-value of Hotelling's T-squared. The ratio of the common area under the graph to the total area of habitat suitability indices was defined as the ecological niche overlap. The results showed significant differences in eye diameter, predorsal, caudal peduncle length, preanal, preventral, ventral-pectoral, body depth, and caudal peduncle depth traits (P < 0.05) in TM, and those differences in the GM were related to the position of the snout, head and body depth and caudal peduncle length i.e., C. damascina had the deeper body shape and head, and anterior the snout and caudal peduncle length. Based on the results, C. damascina prefers areas with higher pH and temperature and by increasing other studied factors, its habitat suitability decreased. The preference for C. umbla with increasing river depth and DO was increased. These two species showed low niche overlap i.e., they avoid competition in their habitat by opting for different areas in terms of river width, flow velocity, and temperature that have more depth with higher slope microhabitats. [ABSTRACT FROM AUTHOR]

One way to increase the thermal efficiency of heat exchangers is to structure the heat transfer surfaces with dimples, resulting in an enlarged surface area and intensified turbulence in the fluid flow. The increased turbulence also causes higher wall shear stress, which potentially suppresses the deposition of particles and supports a self-cleaning of the surface. For a deeper understanding of these phenomena, the flow dynamics inside the dimple were observed experimentally with Stereoscopic Micro-Particle Image Velocimetry (Stereo µPIV). The formation of an unsteady oscillating vortex, which leads to an asymmetric trail downstream of the dimple, is visualized. The significant influence of the dimple geometry on heat transfer enhancement is shown, and the most beneficial geometric ratio of the spherical dimple regarding its ability to increase turbulence is identified. A comparison of the local flow velocities with the results of the numerically and experimentally observed patterns of the deposited particles caused by the dimple's self-cleaning effect shows a good match. [ABSTRACT FROM AUTHOR]

In this paper, we apply a framework based on decomposition techniques to study the synchronization of flow velocity with acoustic pressure and heat release rate in swirl flames. The framework uses the extended proper orthogonal decomposition to identify regions of the velocity field where velocity and heat release fluctuations are highly correlated. We apply this framework to study coupled interactions associated with period-1 and period-2 type thermoacoustic instability in a technically premixed, swirl-stabilized gas turbine-type model combustor operated with hydrogen-enriched natural gas. We find the structures in the flame surface and the heat release rate correlated with the dominant coherent structures of the flow field using extended POD. We observe that the correlated structures in the flow velocity, flame surface and heat release rate fields share the same spatial regions during thermoacoustic instability with period-1 oscillations. In the case of period-2 oscillations, the structures from flame surface and heat release rate field are strongly correlated. However, these structures contribute less to the coherent structures of the flow field. Using the temporal coefficients of the dominant POD modes of the flow velocity field, we also observed 1:1 and 2:1 frequency locking behaviour among the time series of acoustic pressure, heat release rate and the temporal coefficients of the first two dominating POD modes of velocity field during the state of period-1 and period-2 oscillations, respectively. These frequency-locked states, which indicate the underlying phase-synchronization states, correlate with coherent structures in the flow velocity field. [ABSTRACT FROM AUTHOR]

Salt caverns are extensively utilized for storing various substances such as fossil energy, hydrogen, compressed air, nuclear waste, and industrial solid waste. In China, when the salt cavern is leached through single-well water solution mining with oil as a cushion, engineering challenges arise with the leaching tubing, leading to issues like damage and instability. These problems significantly hinder the progress of cavern construction and the control of cavern shape. The primary cause of this is the flowinduced vibration instability of leaching tubing within a confined space, which results in severe bending or damage to the tubing. This study presents a model experimental investigation on the dynamic characteristics of leaching tubing using a self-developed liquid-solid coupling physical model experiment apparatus. The experiment utilizes a silicone-rubber pipe (SRP) and a polycarbonate pipe (PCP) to examine the effects of various factors on the dynamic stability of cantilevered pipes conveying fluid. These factors include external space constraint, flexural rigidity, medium outside the pipe, overhanging length, and end conditions. The experiments reveal four dynamic response phenomena: water hammer, static buckling, chaotic motion, and flutter instability. The study further demonstrates that the length of the external space constraint has a direct impact on the flutter critical flow velocity of the cantilevered pipe conveying fluid. Additionally, the flutter critical flow velocity is influenced by the end conditions and different external media. [ABSTRACT FROM AUTHOR]

Background: Hemodynamic changes are seen in the feeding arteries of arteriovenous malformations (AVMs). Phase-contrast MRI (PC-MRI) enables the acquisition of hemodynamic information from blood vessels. There is insufficient knowledge on which flow or velocity parameter best discriminates AVMs from healthy subjects. Purpose: To evaluate PC-MRI-measured flow and velocity in feeding arteries of AVMs before and, when possible, also after treatment and to compare these measurements to corresponding measurements in healthy controls. Materials and Methods: Highest flow (HF), lowest flow (LF), mean flow (MF), peak systolic velocity (PSV), end-diastolic velocity (EDV), and mean velocity (MV) were measured in feeding arteries in patients with intracranial AVMs using 2D PC-MRI at 3 T. Measurements were compared to previously reported values in healthy individuals. Values in patients above the 95th percentile in the healthy cohort were categorized as pathological. Nidus volume was measured using 3D time-of-flight MR angiography. Results: Ten patients with diagnosed AVMs were examined with PC-MRI. Among these, three patients also underwent follow-up PC-MRI after treatment. Pathological velocities (PSV, EDV, and MV) were seen in all five subjects with a nidus larger or equal to 5.7 cm3, whereas pathological flow values were not seen in all, that is, pathologic HF in three, pathologic LF in two, and pathologic MF in two. After treatment, there was a decrease in flow and velocity (all measured parameters). After treatment, velocities (PSV, EDV, and MV) were no longer abnormal compared to healthy controls. Conclusion: Patients with a large AVM nidus show pathological velocities, but less consistent flow increases. Following treatment, velocities normalize. [ABSTRACT FROM AUTHOR]

Proper assessment of fluid responsiveness using accurate predictors is crucial to guide fluid therapy and avoid the serious adverse effects of fluid overload. The main objective of this study was to investigate the accuracy of respiratory variations in inferior vena cava diameter (∆IVC) to predict fluid responsiveness in mechanically ventilated children. This prospective single-center study included 32 children (median age and weight of 17 months and 10 kg, respectively) who received a fluid infusion of 10 ml kg–1 of crystalloid solutions over 10 min. ∆IVC and respiratory variation in aortic blood flow peak velocity (∆Vpeak) were determined over one controlled respiratory cycle before and after fluid loading. Thirteen (41%) participants were fluid-responders. ∆IVC, ∆Vpeak, stroke volume index, and cardiac index were found to be predictors of fluid responsiveness. However, the area under the ROC curve of ∆IVC was smaller when compared to ∆Vpeak (0.709 vs. 0.935, p < 0.012). The best cut-off values were 7.7% for ∆IVC (sensitivity, 69.2%; specificity 78.9%, positive predictive value, 69.2%; and negative predictive value, 78.9%) and 18.2% for ∆Vpeak (sensitivity, 84.6%; specificity, 89.5%; positive predictive value, 84.6%; negative predictive value, 89.5%). Changes in stroke volume were positively correlated with ∆IVC (ρ = 0.566, p < 0.001) and ∆Vpeak (ρ = 0.603, p < 0.001). A significant correlation was also found between changes in MAP and ∆Vpeak (ρ = 0.382; p = 0.031), but the same was not observed with ∆IVC (ρ = 0.011; p = 0.951). In conclusion, ∆IVC was found to have a moderate accuracy in predicting fluid responsiveness in mechanically ventilated children and is an inferior predictor when compared to ∆Vpeak. [ABSTRACT FROM AUTHOR]

The impulse thruster exhibits the advantages of the simplistic structure and rapid response speed. It is often used for the attitude adjustment and orbit control of the aircraft and space vehicle. In order to study the internal ballistic variation law and the flow characteristics of the gunpowder gas, the interior working process of the L-type impulse thruster was investigated by the numerical simulation and experimental verification. First, an internal ballistic test was designed and conducted, and the change process of the thrust and pressure over time was measured, and the feasibility and rationality of the impulse thruster design were verified. Second, a three-dimensional internal ballistic model of the L-type impulse thruster including the ignition process was established. With the help of the dynamic mesh technology and secondary development capability of the user-defined function in the software Fluent, the coupling process of the propellant combustion and internal flow field change of the gunpowder gas was realized. The calculated results were in good agreement with the test data. Finally, the distribution of the pressure and velocity in the flow field was analyzed in detail, and the variation law of the thrust characteristics with the nozzle length and the expansion ratio was studied, which could provide the essential data for further optimization design research. The outcomes from this paper can offer technical means for advancing studies on the internal ballistic changing law of the L-type impulse thruster. [ABSTRACT FROM AUTHOR]

Heat exchangers (HEs) play a critical role in numerous industrial and engineering applications by facilitating efficient thermal energy transfer. In the pursuit of enhancing the performance of such systems, this study focuses on the hydrodynamic effects of two distinctive vortex generators (VGs) within a turbulent airflow channel, operating under steady-state conditions. Arranged in a staggered manner, the first vortex generator (VG) adopts a rectangular structure positioned in the upper section, while the second VG, triangular in shape, is situated on the opposing wall at varying heights, ranging from 40 to 80 mm in 10 mm increments. A further examination of the triangular VG includes two cases, one featuring an inclined front-face and the other showcasing an inclined rear-face. The turbulent airflow within the channel is accurately represented using the Newtonian fluid model and the standard k-epsilon turbulence model, while the governing equations are solved through the finite element method. A non-uniform mesh, consisting of triangular and square elements with a specific focus on refining the mesh near walls, is designed to capture boundary layer effects and effectively resolve intricacies in near-wall flow dynamics. The investigation unveils dynamic responses within the channel, characterized by notable flow distortions and prominent regions of recirculation, demonstrating the effectiveness of both rectangular and triangular VGs. Importantly, the analysis shows that tilting the triangular VG's back-face notably improves the hydrodynamic structure of the HE channel, leading to enhanced recirculation cells and substantially increased performance. In particular, increasing the height of triangular VGs significantly enhances flow velocity within the channel. For instance, the axial velocity increased by 33.8% when the VG height was raised from 40 to 80 mm in the first triangular case, while an increase of about 37.9% was observed in the second triangular case at the lowest inlet velocity of 7.8 m/s. In addition, triangular VGs with an inclined back-surface achieved higher axial velocities compared to those with an inclined front-surface, with a 13.5% increase at the smallest height and a 17.0% increase at the maximum height. Furthermore, increasing the inlet velocity to 9.8 m/s resulted in a 17.1% higher axial velocity in the second model, reaching 55.4 m/s compared to 47.3 m/s in the first model. These findings underscore the importance of optimizing the triangular VG shape, height, and inlet conditions to maximize the hydrodynamic performance of HE systems, leading to potential energy savings and improved efficiency. [ABSTRACT FROM AUTHOR]

In this study, the dynamical behavior of spinning pipes conveying fluid of axially variable density is investigated. First, based on Hamilton's principle, the coupled governing equations for flexural vibration of the pipe system are derived. Then, the motion equations are truncated by using the Galerkin method. As a result, the discretized motion equations as well as the eigenfrequency equations of the system are obtained. The natural frequencies, divergence, and flutter instability thresholds of the fluid–structure interaction system are acquired by computing the complex frequencies in the first two modes of the system. Also, a comparative study is conducted to validate the accuracy of the present model and solution approach. Finally, the effects of main parameters, such as spinning velocity, flow velocity, mass ratio, and fluid density gradient parameter, on the vibration and stability of the pipe system are evaluated. The results show that the stability of the pipe system is dominated by the mass ratio and the fluid density gradient parameters, while the spinning velocity mainly affects the natural frequency of the system. [ABSTRACT FROM AUTHOR]

A free argon jet flow accompanied by small clusters formation is studied with the direct simulation Monte Carlo method. Some near-continuum flow regimes characterized by Knudsen numbers in the 2 × 10 − 4 − 2 × 10 − 3 range are considered. A model for the argon clusters' growth/decay is proposed, taking into account the phase state of the clusters. The model consists of a chain of reactions leading to the clusters' formation, including the clusters' growth via triple/pair collisions of particles, and the clusters decay according to the collisional/unimolecular mechanism. The cluster size distributions in the jet far field are obtained. The results are compared with two experimental datasets. Good agreement is shown for most of the considered range of parameters. The triple particle collisions' influence on the argon clusters growth process is studied, and their important role in small cluster formation is demonstrated. It has been established that the cluster formation process is limited to an enough small spatial zone near the source outlet, of the order of several exit orifice diameters. The simulation shows a significant influence of cluster formation on the temperature and Mach number distributions, and a weak influence on the flow velocity. The formed clusters' translational temperatures and their velocities are close to the argon atoms' corresponding parameters. A non-equilibrium state, featured by a significant difference between the clusters' internal temperatures and the flow temperature, develops with distance from the source outlet. [ABSTRACT FROM AUTHOR]

The present work investigates granulation or convective flow patterns in density-stratified (or anelastic) convection in spherical shells. The density-stratified thermal convection is typically present in astrophysical systems (such as solar convection); motivated by this, we performed a series of three-dimensional anelastic convection simulations in a spherical shell geometry using an in-house developed hybrid solver. We explored the effect of Rayleigh number and density scale height on the convective flow patterns. The granulation (or cell-like structures) are more prominent at higher density scale height and Rayleigh number. The granulation is further characterized by kinetic energy and helicity spectra. Our results support the argument that the convective flow patterns (or granulation) emerge due to inverse cascade owing to the presence of density stratification. Convective patterns (or granulation) are identified based on length scales, time scales, and flow velocity. The length scale of granules is further verified using a solar granulation model. Our analysis suggests the existence of inverse cascade and supergranulation on the spherical surface due to density-stratified thermal convection in spherical shells. [ABSTRACT FROM AUTHOR]

The bank erosion process in the densely populated Lower Yangtze River can pose a great threat to riparian residents and industries. It is characterized by rapid development within a few hours, a large-scale soil collapse of 106 m3, and an arc shape. During its development, flow field inside the bank erosion area continuously evolves and interacts with the bank soil. However, the mechanisms behind the bank erosion process are still unclear. Therefore, laboratory experiments were conducted to investigate flow structures and turbulences inside bank erosion areas. A pulsed particle image velocimeter was employed to obtain high-quality velocity data inside the bank erosion zone. Results show that the bank erosion zone can be divided into a backflow zone, a mixing zone, and a mainstream zone, according to variations in flow structure; in the mixing zone, water flow is highly turbulent, and the mixing width gradually increases downstream because of the shear effects between the mainstream and backflow; the backflow zone can be subdivided into a central zone and a peripheral zone, based on the pattern of velocity changes along the radial axis from the backflow center to its periphery. A formula for calculating the flow velocity within the backflow zone was proposed, and we found that the velocity gradient in the peripheral zone was approximately four times higher than that in the central zone. This indicated that shear stress exerted by the flow near the backflow boundary was significantly intensified. [ABSTRACT FROM AUTHOR]

Natural channels often take the form of compound channels during flooding events. The unsteadiness of floods is crucial for flood management and river-floodplain ecosystems. However, the impact of unsteady flow on three-dimensional hydrodynamic processes within compound channels remains poorly understood. This study employed a validated two-dimensional/three-dimensional numerical model to examine how unsteady features influence key hydrodynamic indicators of compound channels, such as velocity distribution, turbulence characteristics, and discharge partitioning between the main channel and floodplain. A definitive positive correlation was found between water level fluctuation amplitudes and integrated discharge during unsteady events, as well as between mean water levels and mean discharges. The proportion of discharge conveyed by the main channel relative to the total was directly linked to the water depth ratio. The exchange at the main channel–floodplain interface exhibits a dual-layer flow pattern: surface waters spill into the floodplain, while deeper waters are siphoned into the main channel. Unsteady conditions principally modulate the intensity of these exchanges, altering hydraulic interactions and water transfer between areas. Pronounced wall shear stresses were detected at the main channel–floodplain interface due to swift channel flows and momentum exchange at the floodplain margin, with maxima adjacent to the floodplain edge correlating with peak flow velocities. Under deep conditions, cross-sectional flow across the compound channel's mixing layer was essentially two-dimensional. These findings elucidate the complex hydrodynamics inherent to unsteady overbank flows while holding implications for enhancing floodplain management and advancing the understanding of unsteady fluvial hydraulics. [ABSTRACT FROM AUTHOR]

Precessing vortex core (PVC), a typical vortex structure, universally exists in swirling flow fields and originates from the Kelvin–Helmholtz instability of the swirling shear layer. In the combustion chamber, pressure pulsations from PVC might resonantly couple with acoustic modes, leading to thermoacoustic oscillations which is a significant challenge in the development of rocket engines and gas turbines. The present work focuses on the time-averaged and unsteady flow characteristics of different swirling flow fields in the premixed swirling combustor. The PVC observed in the swirlers adopted presents a single helical structure and the PVC frequency is proportional to the incoming flow velocity. Moreover, another low-frequency helical mode located in the downstream region of the flow fields has been identified and categorized as PVC type II to be distinguished with common PVC mode in this study, which originates from the precession of the central recirculation zone. The experimental results further emphasize the effects of the swirling injector geometry on PVC and the low-frequency helical modes. This indicates that as the diameter of the bluff body or the divergence cup angle increases, the energy of the PVC mode decreases while that of the helical mode increases significantly. In addition, the PVC mode would be gradually suppressed as the tail size of the bluff body increases. These results, especially the coexistence of the PVC mode and the low-frequency helical mode, are rarely reported in previous studies, and they may provide an effective guidance for investigating the mechanism and control of thermoacoustic oscillations. [ABSTRACT FROM AUTHOR]

We investigate the effectiveness and universality of the turbulence control strategy for wall-bounded shear flows proposed by Chagelishvili et al. The basis of this strategy is the continuous seeding of the flow viscous sub-layer with spanwise asymmetric and specially designed velocity perturbations. This seed velocity field, amplifying due to the shear flow non-normality, breaks the flow spanwise reflection symmetry, specifically leading to the generation of a secondary nonuniform spanwise mean flow, which significantly reduces the flow turbulence. For now, this strategy is realized by a weak near-wall volume forcing, which, though theoretical/hypothetical, initiates the needed seed velocity field in the flow. To confirm the practical significance of this control strategy, we evaluated its effectiveness in the plane Couette flow at various Reynolds numbers, and with the forcing locations at different distances from the wall. The universality of the discussed turbulence control strategy is shown through the direct numerical simulations. The simulations with the near-wall volume forcing having specially designed, fixed configuration and amplitude result in the reduction of turbulence kinetic energy production by 30%–40% across a wider range of Reynolds numbers, R e τ = 52 , 92 , 128 , and 270 , and the forcing various wall-normal localizations in plus units, y peak + = 0.16 , 0.28 , 0.38 , 0.81 , 2.56 , and 2.76. [ABSTRACT FROM AUTHOR]

Enhancing mixing efficiency in microscale processes for sensitive biomedical, pharmaceutical, and chemical applications is crucial, particularly when operating under low-velocity constraints. This study presents a comprehensive investigation into the impact of various factors on microfluidic mixing within a circular mixing chamber micromixer, utilizing electroosmotic principles. The governing equations are solved numerically using the finite element technique-based solver. This research examines the effects of microchamber diameter (D), inlet velocity (uo), alternating current (AC) voltage amplitude (ϕo), and AC frequency (f) on fluid mixing dynamics. Several key findings are noted from this study. The reduction of the circular microchamber diameter decreases the linear distance between cross-reciprocally placed microelectrodes, resulting in increased electroosmosis force and mixing efficiency. The voltage amplitude within the specified range shows increased mixing efficiency when fluid species are combined at appropriate velocity and AC frequency. The highest mixing efficiency of 98.84% is achieved with the following parameters: flow velocity (uo) of 150 μm/s, AC frequency of 4 Hz, voltage amplitude of 500 mV, and microchamber diameter of 20 μm. At a frequency of 12 Hz and voltage amplitude of 500 mV, the mixing efficiency exceeds 94.66% across a wide range of input velocities (100–200 μm/s), enabling versatile control in microfluidic devices. The nonlinear interaction between electroosmotic flow and microchamber geometry significantly contributes to this enhanced mixing efficiency. These results demonstrate the potential for optimizing microfluidic mixing processes through careful parameter tuning, particularly in applications requiring high efficiency at low flow rates. Thus, this study provides valuable insights for designing more effective microfluidic systems in various scientific and industrial fields. [ABSTRACT FROM AUTHOR]

As the impact force of a flow overcomes the frictional resistance of an object, the object moves as long as the pressure exerted by the flow is greater than its shear resistance. With this concept, here, we develop simple analytical models for the mechanical description of the coefficient of impact pressure C p 0 and the mobilization length L when a mass flow impacts a movable object. We invented the obstacle mobilization number C p 0 , a dimensionless number, which is expressed as the ratio of the obstacle shear resistance to the kinetic energy of the flow, per unit length. We also relate it to the obstacle Froude number Fr0. When the object moves through the length L against the basal friction, after consuming its kinetic energy, the object eventually stops. This balance between the kinetic energy and friction yields an analytical model for the mobilization length of the object. Equivalently, if the mobilization length is known, the impact velocity can be calculated. This is very important in estimating the flow velocity of any large-scale natural mass flows. Our model predicts that C p 0 decreases strongly to weakly non-linearly with the impact velocity, density ratio between the granular particle and the mobile object, and the area ratio between the grain covered area of the object and its base. Moreover, C p 0 increases linearly with the basal friction coefficient. However, the dynamic response of C p 0 to the shape of the object may vary immensely between objects of different shapes. Our model also predicts that the mobilization length L of the mobile object varies with the square of the impact velocity of flowing mass, but decreases with basal friction of the obstacle and the component of gravitational acceleration in the direction normal to the flow depth. We conduct several laboratory chute experiments with different native Nepalese complex fruit seeds and food grains to validate the physical significance and scope of C p 0 and L. Our simple analytical models very well describe the coefficient of impact pressure and the mobilization length of the mobile object impacted by the laboratory granular flows. We discuss the applicability of C p 0 and L to real flow situations in designing protective civil defense structures as well as mitigating from natural disasters, and industrial transports of complex granular flows. [ABSTRACT FROM AUTHOR]

The motion of a deformable compound droplet flowing within a confined channel in response to a pulsatile flow is numerically investigated. Toward this, an in-house solver based on the level-set method is developed. It is shown that a low Strouhal number leads to significant oscillation in flow velocity and a greater deformation of the compound droplet, driving it periodically along the streamwise direction resulting in an increased residence time, as compared to steady imposed flow. Conversely, high Strouhal number results in smaller amplitude oscillations in flow velocity leading to smoother droplet motion and lower deformation. Expectedly, a decrease in the pulsatile flow amplitude yields smoother and more uniform flow with reduced droplet deformation. Importantly, hitherto unreported cross-stream migration of an off-centered compound droplet under pulsatile flow is investigated. An off-centered compound droplet migrates toward the center of the channel, with its core being eccentric toward the wall it was initially close to. The influence of other key parameters such as density ratio, size ratio of the core, and the viscosity ratio of the shell in shaping the dynamics of the compound droplet is systematically explored. It is revealed that the eccentricity of the core can be manipulated by tuning inlet flow and density of core fluid. A more viscous shell results in a marginally higher film thickness near the wall and a higher droplet residence time within the channel. A higher Bond number results in a larger droplet deformation, resulting in a streamlined shape and significantly higher droplet speed. [ABSTRACT FROM AUTHOR]

The flow mechanism of internal two-phase flow atomization remains unclear despite its widespread applications. A newly outside-in-liquid (OIL) atomizer is designed to investigate the two-phase flow mechanism inside the effervescent atomizer in this work. Numerical simulation is used to study the internal flow characteristics of the OIL atomizer under different gas–liquid mass flow ratios (GLRs). The findings indicate that the volume-of-fluid (VOF) model and compressible Euler method effectively capture the intricate evolution of the internal flow. The cavitation phenomenon occurs before the gas phase reaching the orifice. Subsequently, the cavitation phenomenon disappears as the gas phase flows downstream into the orifice. At different GLRs, the gas phase before reaching the mixing chamber is a single separated bubble. However, the final flow patterns are mainly annular flow, which is most obvious at high GLR. Increasing the GLR can increase the gas void fraction in the orifice. Furthermore, the gas void fraction will reach the peak faster and then remain stable. The two phases are accelerated after entering the orifice. Among them, the flow velocity of gas phase is much higher than that of liquid phase. This research demonstrates the notable impact of GLR on the internal flow. Furthermore, it addresses the existing research gap in this aspect of internal flow. [ABSTRACT FROM AUTHOR]

Volcanic eruptions can bring about lava flows, posing significant hazards and rare direct threats to human life, but they can also cause extensive damage to property and economic activities. Managing volcanic disasters demands swift and accurate information on the behaviour and evolution of lava flows, particularly regarding their extension, displacement, and trajectory. This study addresses numerical and laboratory modelling to understand the dynamics of a lava flow and its frontal advancement. Laboratory experiments of a lava flow analogue, exhibiting a non-Newtonian Herschel–Bulkley fluid behaviour, have been conducted. The fluid parameters at varying temperatures have been determined on the basis of the rheometer and thermal camera measurements. A flow of the Herschel–Bulkley fluid (the lava flow analogue with the fluid parameters determined from the laboratory experiments) is then simulated numerically using the Abaqus software, where a smoothed particle hydrodynamics method has been implemented. A run-out distance, frontal flow displacement, and flow velocity have been determined during laboratory and numerical modelling. When the fluid parameters measured at a constant temperature of 80°C are used, the numerical results diverge from the experimental results over time. To mimic closely the dynamics of the lava flow analogue inferred from the laboratory experiment with its dynamics in the numerical modelling, time-dependent adjustments to the Herschel–Bulkley fluid parameters determined at lower temperatures have been introduced by changing their values during a numerical simulation. This study underscores the importance of constraining parameters of numerical models by the values obtained from laboratory measurements. [ABSTRACT FROM AUTHOR]

Objectives: Cardiovascular magnetic resonance (CMR) imaging is routinely performed for assessing right ventricular (RV) systolic but not diastolic function. We aimed to investigate CMR-based assessment of RV diastolic function in pediatric patients with repaired tetralogy of Fallot (rTOF), compared to transthoracic echocardiography (TTE) measurements. Methods: A total of 130 consecutive pediatric patients with rTOF who underwent clinically indicated CMR and same-day TTE were included. Forty-three controls were recruited. Phase-contrast images were used to measure trans-tricuspid valve flow velocities during early (E) and late diastolic (A) phases (measured in cm/s). Feature tracking of the tricuspid annulus was performed to derive early (e′) and late diastolic (a′) myocardial velocities (measured in cm/s). RV diastolic function was evaluated by E/A ratio, E/e′ ratio, and E-wave deceleration time (measured in milliseconds). Regression analyses were utilized to identify potential variables associated with RV diastolic dysfunction (DD). The performance of CMR-derived parameters in diagnosing RV DD was assessed using receiver-operating characteristic analyses. Results: Good agreement was found between CMR and TTE measurements (ICC 0.70–0.89). Patients with RV DD (n = 67) showed significantly different CMR-derived parameters including E and e′ velocities, and E/A and E/e′ ratio, compared to patients without DD (n = 63) (all p < 0.05). CMR-derived E and e′ velocities and E/e′ ratio were independent predictors of RV DD. E/e′ of 5.8 demonstrated the highest discrimination of RV DD (AUC 0.76, sensitivity 70%, specificity 86%). Conclusions: CMR-derived parameters showed good agreement with TTE parameters in determining RV DD. CMR-derived E/e′ was proved to be the most effective in identifying RV DD. Clinical relevance statement: This study demonstrated the feasibility and efficacy of CMR in assessing diastolic function in pediatric patients. RV DD was presented in over half of patients according to current TTE guidelines, highlighting the need for assessing RV diastolic function during follow-up. Key Points: • Routinely acquired cine and phase-contrast cardiovascular magnetic resonance (CMR) images yielded right ventricular (RV) diastolic parameters which demonstrated good agreement with transthoracic echocardiography (TTE) measurements. • There was a high prevalence of RV diastolic function impairment in pediatric patients with repaired tetralogy of Fallot (rTOF). • CMR is a reliable complementary modality of TTE for RV diastolic function evaluation. [ABSTRACT FROM AUTHOR]

Hydraulic transient analysis through numerical simulations is a widely used tool for predicting and mitigating potential severe pressure oscillations due to abrupt changes in flow velocity. In practice, water hammer events typically are induced by valve operations used to control the flow rate. One of the methods to enhance the throttling capabilities of a gate valve is to install a V-shaped notch (V-port) in its opening. This provides a more linear relationship between the position of the gate and the flow rate discharging through the valve. The exact range of the flow control is determined by the V-port opening angle. Because valve-induced pressure oscillations depend on the valve characteristics, in order to accurately simulate the transient event, the specific valve closing function is required. The primary objective of this paper was to develop valve closing functions of V-port gates for all possible opening angles. Two cases were considered: the linear closure of a knife (rectangular) and a circular gate fitted with a V-port. For this purpose, the analytical formulas for calculating the relative opening area of V-shaped gate valves were derived. On this basis, valve closing functions, in the form of a power function with two variables, were developed. To analyze the influence of the V-port angle on a simulated transient event, a case study with a simple reservoir–pipeline–valve system was investigated. One-dimensional unsteady flow equations were solved using the method of characteristics. The numerical calculations conducted indicate that installing a V-notch port can result in a smoother reduction of the flow rate as the gate closes, which may dampen both maximum and minimum pressure peaks and attenuate valve-induced pressure head oscillations. The developed valve closing functions offer practical utility for practitioners engaged in hydraulic system design and operation, providing a tool for predicting hammer events induced by valve gates fitted with V-ports. [ABSTRACT FROM AUTHOR]

Flushing is a widely used method for cleaning water pipes, demanding the achievement of optimal flushing velocity for effectiveness. A prior examination of flushing condition including velocity, duration, and flow rate is crucial to minimize water and economic losses while maximizing the impact of flushing. Although simulation models are commonly employed for this purpose, they often overlook potential head loss during flow through hydrants or drain valves, compromising the effectiveness of flushing. This study investigated the impact of different simulation methods on estimating flushing conditions through hydrants and drain valves. The structural layout (minor loss coefficient) and specifications (emitter coefficient) of each flushing path were incorporated into traditional models. Applying this method to a hypothetical network and the water distribution system of G-City in Gyeonggi Province of South Korea, we compared the flushing effects of four different modeling approaches. Results reveal that drain valves tend to exhibit higher velocity than hydrants under the same conditions, mainly due to their structural layout. However, both drain valves and hydrants may experience overestimation of flow rate and velocity if the minor loss coefficient is disregarded. Practitioners should exercise caution regarding potential low flushing efficiencies. The limited numbers and locations of drain valves compared to hydrants constrain their field application, emphasizing the need for comprehensive consideration of various field conditions when developing a suitable flushing plan. [ABSTRACT FROM AUTHOR]