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To improve estimation of sea salt deposition distributions on structural surfaces such as that of an airborne sea salt and corrosion sensor, we numerically simulated approaching flows with particles around a vertical flat plate. This is a typical object that mimics a sensor with a support plate. We used a computational fluid dynamics (CFD) model based on the unsteady Reynolds averaged Navier-Stokes equation. After validating the results by comparison with existing studies for flows with particles around a cylinder, we examined the changes in particle impaction efficiency on the plate with different approaching flow directions (0, 45 deg) and particle diameters (5 © 10-6-1.6 © 10-4 m). The impaction efficiency increases rapidly with particle diameter, whereas the influence of flow direction is small. Such increases in impaction efficiency are due to contributions from inertial impaction, and thus the variation in Stokes number with wind speed and the plate size can be used to predict the flow and particle conditions required for increases in impaction efficiency. The efficiencies for small particles on the front surface of the plate are higher than those on a cylinder. The impactions of small particles on the plate are locally activated by flow separations around a bluff body, whereas those on a cylinder are caused by intercepts without flow separations. [ABSTRACT FROM AUTHOR]

The jet impingement flash technology represents a paramount research subject in the domain of heat and mass transfer. To augment its commercial potential, the conjunction of annular multi‐aperture jet impingement with negative pressure flash evaporation is introduced in this study. The employment of an annular nozzle array is integral to the enhancement of the heat and mass transfer efficiency between the phases. The Realizable k‐ε model is used in this study. The negative pressure flash vaporization model was also developed by introducing a mass source term and an energy source term based on the Mixture model. The flow characteristics are characterized using numerical simulation. Additionally, the λ2 vortex identification criterion is investigated the vortex structure. The simulation results exhibit good agreement with experimental findings, demonstrating that a higher initial vacuum leads to a stronger flashing effect and a more chaotic movement of the flow group within the flow field. Thus, this study provides a reference method for the structural design and optimization of annular symmetric jet impingement negative pressure deammonia chemical equipment for engineering applications. [ABSTRACT FROM AUTHOR]

In order to determine the most suitable turbulence model for studying the aerodynamic performance of bus, the effects of different turbulence models on the aerodynamic characteristics of bus were investigated. A comparative analysis was conducted on five turbulence models (IDDES, DDES, DES, LES, URANS). The pressure distribution on the cross section at x=0 and y=0 is also analyzed for each model. The results reveal that IDDES accurately captures the negative pressure at the rear of the bus and predicts the pressure gradients more effectively than other models. IDDES also captures more vortices at the head of the bus and predicts the wake flow more widely than other models. DDES has obvious shedding phenomenon in the wake flow, while IDDES provides a relatively smooth airflow trajectory, but its prediction of airflow trajectory at a distance is less clear. Through quantitative and qualitative analyses of the aerodynamic characteristics of bus under different turbulence models, it can be concluded that IDDES is the most suitable turbulence model to study the aerodynamic characteristics of bus. [ABSTRACT FROM AUTHOR]

In order to determine the most suitable turbulence model for studying the aerodynamic performance of bus, the effects of different turbulence models on the aerodynamic characteristics of bus were investigated. A comparative analysis was conducted on five turbulence models (IDDES, DDES, DES, LES, URANS). The pressure distribution on the cross section at x=0 and y=0 is also analyzed for each model. The results reveal that IDDES accurately captures the negative pressure at the rear of the bus and predicts the pressure gradients more effectively than other models. IDDES also captures more vortices at the head of the bus and predicts the wake flow more widely than other models. DDES has obvious shedding phenomenon in the wake flow, while IDDES provides a relatively smooth airflow trajectory, but its prediction of airflow trajectory at a distance is less clear. Through quantitative and qualitative analyses of the aerodynamic characteristics of bus under different turbulence models, it can be concluded that IDDES is the most suitable turbulence model to study the aerodynamic characteristics of bus.

Hydrogen ejectors effectively utilize excess unreacted hydrogen. However, traditional ejectors have limited operational ranges and are only suitable for specific power ranges. This paper presents a dual-nozzle ejector aimed at broadening its operational range through different working modes. A simulation model, validated by experiments, is employed based on the working principles of ejectors. Spiral blades are installed at drive end to improve the recirculation efficiency. Flow characteristics, including streamwise and spanwise vortices at high power, are also investigated in different modes. Results indicate that optimal operating range for Ring-nozzle(RN) mode is between 31.1 and 124.4A. When output current exceeds 124.4A, it is necessary to switch to Central-nozzle (CN) or Double-nozzles (DNs) mode. Analysis of streamlines and velocity vectors reveals that installing spiral blades can modify directions of primary flow. Blades with appropriate distortion should be selected. In CN mode, when stack reaches 60% of rated power, installing 20° spiral blades has a minimal impact on stability of radial flow. Installing 30° or 40° spiral blades is suitable for full-load condition. In DNs mode, installing 30° spiral blades enhances acceleration of gas flow with lower influence from radial influx. This ejector provides assurance for upgrade of fuel cell stacks by incorporating recirculation technology. • A dual-nozzle ejector with spiral guide blades is designed, verified and evaluated. • Installed spiral blades change direction and gather kinetic energy of primary flow. • Advantageous working conditions of different modes with blades are discussed. • Flow mechanism of different blades under high power in two modes is analyzed. • Flow acceleration and losses should be balanced by changing the twist of blades. [ABSTRACT FROM AUTHOR]

One of the structures for regulating the water level in the irrigation and drainage ducts is the lopac gates, which are proposed as a structure for regulating and controlling the flow level. In this study, a new design of this type of structure has been proposed in which the gates are placed next to each other in pairs, and they are called multiple lopac gates. The objective of this research is to investigate the effective hydraulic parameters of the proposed structure and compare it in a case where a gate is used under the same conditions. All the simulations were modeled with 3 amounts of opening 30, 45, and 60 degrees and at 3 flow rates of 20, 40, and 60 liters per second and using Flow3d software, in these simulations, the number of mesh cells is 1000000 and RNG turbulence model is used. The results showed that the maximum shear stress was reduced by an average of 38% compared to the single gate mode in most tests at different openings and flow rates using multiple lopac gates, and the largest amount of this reduction was related to the opening of 45 degrees, and the flow rate is 40 liters per second with a value of 76%. Also, the forces acting on the gate at different flow rates and openings will be reduced by 150% on average. In the qualitative investigation of flow vortices, the investigations also showed that vortex range, length, and strength are reduced compared to the single gate mode when two gates are used, and the number of vortices increases compared to when a single valve. [ABSTRACT FROM AUTHOR]

Multi-principal element alloys (MPEAs) exhibit outstanding strength attributed to the complex dislocation dynamics as compared to conventional alloys. Here, we develop an atomic-lattice-distortion-dependent discrete dislocation dynamics framework consisted of random field theory and phenomenological dislocation model to investigate the fundamental deformation mechanism underlying massive dislocation motions in body-centered cubic MPEA. Amazingly, the turbulence of dislocation speed is identified in light of strong heterogeneous lattice strain field caused by short-range ordering. Importantly, the vortex from dislocation flow turbulence not only acts as an effective source to initiate dislocation multiplication but also induces the strong local pinning trap to block dislocation movement, thus breaking the strength-ductility trade-off. [ABSTRACT FROM AUTHOR]

We propose a method for calculating the kinetics of ultrasonic coagulation of PM2.5 during fine gas cleaning that provides an order of magnitude higher calculation performance. Increased productivity is achieved through the proposed and justified method of reducing the original three-dimensional problem to a two-dimensional one. The proposed reduction method is based on the fact that the time of complete rotation of vortex acoustic flows turns out to be much shorter than the characteristic coagulation time during fine gas cleaning. This makes it possible to present the fractional composition of aerosol particles as a function of two stream functions instead of three coordinates. Calculations carried out using the proposed method make it possible to identify the possibility of increasing the efficiency of coagulation in three-dimensional flows due to the following mechanisms: a local increase in concentration caused by the inertial transfer of particles to the periphery of three-dimensional vortices in the gas phase, increasing the frequency of particle collisions due to three-dimensional turbulent disturbances in ultrasonic fields with a high amplitude of oscillatory velocity (more than 10 m/s), and increasing productivity and ensuring the possibility of continuous implementation of the process in flow mode due to the transfer of particles between the streamlines of the main vortices initiated by ultrasonic vibrations as well as due to external flows perpendicular to the plane of the vortices in three-dimensional space. The developed set of programs for implementing calculations can be used in the design of gas cleaning equipment. [ABSTRACT FROM AUTHOR]

The objectives of this paper are to pursue an accurate numerical method of unsteady cavitating flow at a reasonable calculation cost and investigate the unsteady cavitating flow characteristics of a centrifugal pump. Firstly, the cavitating flow simulations of a centrifugal pump were performed using the partially-averaged Navier–Stokes (PANS) turbulence model and its improved model to evaluate the numerical methods based on experimental data. Compared with the experimental results, the improved PANS turbulence model can better predict the cavitating flows in the pump and has better applicability. Further, the unsteady cavitating flow characteristics of the centrifugal pump, such as the vapour volume fraction, the cavitation-vortex dynamics and the pressure and head fluctuations, were simulated by improved PANS model and discussed. The liquid flow vortex at the end of the cavitation in the impeller is an important reason for the periodic change of the cavitation shape. The periodic change of cavity volume has a certain impact on the pressure pulsation in the impeller and the pump head. [ABSTRACT FROM AUTHOR]

Objectives: Blood‐flow pattern is an essential factor in cardiovascular development. Recently, blood speckle‐tracking echocardiography (BST) based on high‐frame‐rate ultrasound has emerged as a promising technique for the assessment of blood‐flow patterns and properties. The objectives of this study were to determine the feasibility of BST in the fetus and to assess intracardiac blood‐flow patterns of fetuses with a congenital heart defect (CHD) using this technique. Methods: This was a prospective study consisting of 35 normal fetuses, 35 fetuses with left‐sided obstructive lesion (LSOL) and 35 fetuses with right‐sided obstructive lesion (RSOL). BST images of fetal intracardiac regions of interest (ROIs), including the left ventricle (LV), right ventricle (RV), ascending aorta (AAo), aortic arch (AA), descending aorta (DAo) and pulmonary artery (PA), were obtained and analyzed. The feasibility of BST was assessed, and blood‐flow pattern and number of vortices in the ROIs were recorded. Results: The median gestational age of the fetuses was 24.7 weeks (range, 19.6–34.3 weeks). BST was feasible in 81.6% of cases, and the cut‐off value of depth for an adequate BST image was ≤ 7.9 cm. There were no differences in the presence of vortex/turbulent blood flow in the LV or RV among the three groups. Vortex/turbulent blood flow in the AAo was detected in 0% (0/35), 14.3% (5/35) and 57.1% (20/35) of cases in the control, LSOL and RSOL groups, respectively. The respective values were 5.7% (2/35), 14.3% (5/35) and 51.4% (18/35) for the AA; 0% (0/35), 48.6% (17/35) and 0% (0/35) for the DAo; and 0% (0/35), 40.0% (14/35) and 51.4% (18/35) for the PA. With the exception of the DAo in the RSOL group, vortex/turbulent flow in the great artery ROIs was significantly more common in the LSOL and RSOL groups than in controls (P < 0.01). In the LSOL group, the number of vortices in the AAo, AA, DAo and PA was significantly greater compared with that in controls (P < 0.01). In the RSOL group, the number of vortices in the LV, AAo, AA and PA was significantly greater compared with that in controls (P < 0.01). Conclusions: Fetuses with CHD were more likely to exhibit vortex/turbulent blood flow and increased number of vortices in the great arteries compared with healthy controls. Further research is needed to determine the biomechanical effect of blood‐flow patterns, especially vortex flow, on fetal cardiovascular structure and function. © 2023 International Society of Ultrasound in Obstetrics and Gynecology. [ABSTRACT FROM AUTHOR]

The evolution of unforced and weakly damped two-dimensional turbulence over random rough topography presents two extreme states. If the initial kinetic energy E is sufficiently high, then the topography is a weak perturbation, and evolution is determined by the spontaneous formation and mutual interaction of coherent axisymmetric vortices. High-energy vortices roam throughout the domain and mix the background potential vorticity (PV) to homogeneity, i.e., in the region between vortices, which is most of the domain, the relative vorticity largely cancels the topographic PV. If E is low, then vortices still form but they soon become locked to topographic features: Anticyclones sit above topographic depressions and cyclones above elevated regions. In the low-energy case, with topographically locked vortices, the background PV retains some spatial variation. We develop a unified framework of topographic turbulence spanning these two extreme states of low and high energy. A main organizing concept is that PV homogenization demands a particular kinetic energy level E#. E# is the separator between high-energy evolution and low-energy evolution. [ABSTRACT FROM AUTHOR]

Diverting or deflecting sediments is an essential part of river training. Under the effect of an induced helical motion, the submerged vanes are best known for deflecting sediments. This study presents current state-of-the-art information on employing submerged vanes for sediment deflection, as well as concluding notes outlining the current knowledge's limitations and suggestions for future research on sediment deflection using submerged vanes. The analytical background for basic physics of submerged vanes' operation is first described. The paper then moves on to a thorough examination of vane design parameters based on analytical relationships. A brief overview of the applications of submerged vanes is also included in the paper. A review of recent studies aims at designing a layout of submerged vanes to assist in river training tasks, such as river bends protection, sediment exclusion at water intakes, improving safety at bridges on waterways, improving inland navigation is provided to this end. The study also presented a future program of research on submerged vanes for improving inland navigation in braided rivers. The major lag in literature is a lack of information on macro turbulence and the associated sediment motion induced by the wake of the submerged vane. [ABSTRACT FROM AUTHOR]

In order to improve the yield of steel produced in the converter and the quality of the molten steel, and to understand the distribution of the flow field in the converter and ladle during the steelmaking process, the CFD fluid simulation software Fluent 2020 R2 was used to analyze the flow field of the converter static steelmaking process. The aperture of the steel outlet and the timing of the vortex formation under different angles were studied, as well as the disturbance level of the injection flow in the ladle molten pool. The study revealed that in the steelmaking process, the emergence of tangential vectors caused the entrainment of slag by the vortex, whereas in the later stages of steelmaking, the turbulent flow of slag disrupted the vortex, resulting in its dissipation. When the converter angle increases to 90°, 95°, 100°, and 105°, the eddy current occurrence time is 43.55 s, 66.44 s, 68.80 s, and 72.30 s, and the eddy current stabilization time is 54.10 s, 70.36 s, 70.95 s, and 74.26 s, respectively. When the converter angle is 100–105°, it is suitable to add alloy particles into the ladle molten pool. When the tapping port diameter is 220 mm, the eddy current inside the converter changes and the mass flow rate of the tapping port is "oscillating". When the aperture of the steel outlet was 210 mm, the steelmaking time could be shortened by about 6 s without affecting the internal flow field structure of the converter. [ABSTRACT FROM AUTHOR]

This study aims to investigate the impact of cavitation states on the stability of cryogenic pumps. Steady and unsteady simulations of the internal flow were conducted based on an SST k–ω turbulence model and a modified Zwart cavitation model considering thermodynamic effects. The modified cavitation model was verified using the hydrofoil model and compared with the Hord test results. The results indicate that the variation in pressure at the pump inlet has a significant influence on the cavitation in the pump. The cavitation states and fluid flow directions vary across the different spans in the impeller channel. The smaller the distance from the front cover of the impeller, the more severe is the cavitation, in addition to the appearance of a vortex. The influence of the formation of a longitudinal vortex at the impeller outlet on the pressure fluctuation in the cavitation state was revealed. The rotation of the impeller has negligible influence on the pressure load distribution at the blade inlet. However, it has a higher influence on that of the second half of the blade, particularly when the blade passes through the volute tongue. Cavitation can exacerbate the instability of pump operation. The research results are significant for accurately predicting cavitation performance and improving the anti-cavitation capability of cryogenic pumps. [ABSTRACT FROM AUTHOR]

The Liutex vector is new quantity introduced to represent the rigid-body rotation part of fluid motion and thus to define and identify vortices in various flows. In this work, the intermittency and power-law similarity of the Liutex vector in homogeneous, isotropic turbulence and a turbulent channel are explored. First, we found that the Liutex vector is more intermittent than the vorticity vector in the considered turbulent flows, which indicates that an iso-surface of a Liutex magnitude with an appropriate threshold could capture the major rotating motions or vortical motions of the flow. Second, the three-dimensional energy spectrums of velocity, vorticity (enstrophy spectrum) and the Liutex vector in homogeneous isotropic turbulence are shown to exhibit power laws of −5/3, 1/3 and 1/3 in the inertial subrange, respectively, whilst the Liutex energy spectrum particularly satisfies an additional −10/3 power law in the viscous subrange. This viscous similarity of the Liutex vector is the only power law that survived from the wall presence and is argued to originate from the fact that the Liutex vector represents the rigid part of fluid motion and is free from any shear contamination. The existence of such a viscous similarity law indicates a certain coherence of the small scales of turbulence and could possibly help understand and model turbulence. [ABSTRACT FROM AUTHOR]

Heat transport in rotating processes finds a wide range of application in which academic issues in the fluid mechanics and heat transfer areas are here reported. This paper discusses successive works from the seminal paper of Taylor (1923) to recent numerical results established from a broad range of methods such as DNS, LES, RANS or LB methods. The flow regimes identification is thus reported in Taylor–Couette geometry. The role of the axial flow rates in the apparition, stabilization and destruction of the large-scale of the turbulent structures is depicted in the case of Taylor–Couette–Poiseuille geometry. In a non-isothermal condition, a discussion is held on the various exponent values found in the scaling relationships relying on the Nusselt number as a function of the Rayleigh or Reynolds numbers according to the regimes of thermal convection. [ABSTRACT FROM AUTHOR]

The effects of a Trapped Vortex Cavity (TVC) on the aerodynamic performance of a NACA 0024 airfoil at a constant angle of attack (AoA) of 14◦ were investigated in this study. It was observed that mass suction (MFR) was required to stabilise the vortex within the cavity segment. Lift to drag ratio (L/D) and MFR were chosen as performance objectives, along with a fully attached flow constraint (flow separation at X/c ≥ 95% ). Parametric analysis was carried on the baseline airfoil with and without suction and compared to the airfoil with TVC with and without suction. It was observed that L/D increases as MFR increases for a baseline airfoil, and flow separation is delayed at high suction values (MFR = 0.2 kg/s). The TVC modifies the pressure distribution on the baseline airfoil when MFR is applied to the cavity section and there is a significant increase in lift; thus, L/D increases and flow separation is delayed. A lower value of MFR = 0.08 kg/s is sufficient to stabilise the vortex and improve the efficiency of the TVC airfoil. The findings of these parametric studies were used to do a multi-objective optimisation using a genetic algorithm to attain the desired cavity shape while achieving the largest L/D and the lowest MFR (that is proportional to the power required for control) with a fully attached flow constraint. It was found that mass suction and cavity shape both had an equal influence on flow control. The Pareto optimal front yielded a series of optimum designs. One of them was subjected to an off-design analysis in order to validate its performance at other incidences. It was observed that it performs better than the baseline airfoil, with an improved L/D and an increase in stall angle from 10◦ to 14◦.

• A novel leading edge winglet is proposed to improve the flow patterns in the highly loaded turbine. • The geometric parameters of the leading edge winglet are investigated by comparing the efficiency and local flow loss. • The flow mechanism of the winglet is explained from the perspective of the vortex strength and scale. In order to decrease the flow loss of the region close to the endwall, a novel leading-edge modification strategy is proposed in this paper. Specifically, the winglet is installed at the leading edge of the first-stage blade of the highly loaded PW-E3 (Energy Efficient Engine designed by Pratt & Whitney Aircraft Group) turbine. The numerical methods used in this study are validated with the experimental data of the original blade profile of PW-E3. The SST (Shear Stress Transport model) γ-θ turbulence model is employed to calculate the flow field. The schemes of the forward bending winglet and reverse bending winglet are compared with the base case to prove the superiority of this modification strategy. The numerical results indicate a significant increase in stage efficiency by reducing the total pressure loss coefficient. Reverse bending winglets perform better than forward bending ones in terms of efficiency promotion. The effects of the normalized winglet height and bending angle are further explored. For reverse bending winglets, increasing the normalized winglet height and bending angle leads to improved flow control. Conversely, for forward bending winglets, reducing the normalized winglet height and bending angle is more favorable for loss reduction. [ABSTRACT FROM AUTHOR]

A numerical study of the aerodynamics of a swirling turbulent flow and of the classification of particles in the vortex chamber of a pneumatic combined apparatus has been performed. The obtained results indicate the possibility of achieving a uniform distribution of the radial flow velocity along the height of the chamber in the particle separation zone in it by changing the shape of the rotor blades of the apparatus, which is a prerequisite for its efficient operation. The trajectories of motion of single particles in the vortex chamber are determined. A significant effect of turbulent flow pulsations on the efficiency of particle separation in it has been established. The reliability of the obtained results is confirmed by test studies and by their comparison with experimental data. [ABSTRACT FROM AUTHOR]

This research present an analysis of the decomposition of Laguerre-Gaussian modes into Hermite-Gaussian modes when propagating through turbulence. This effect can be clearly observed by canceling the original Laguerre-Gaussian beam with another of different topological charge. The results of the propagations of these beams through Kolmogorov turbulence phase masks were analyzed, identifying which ones achieved the decomposition. The turbulences were then decomposed into the first 15 Zernike polynomials and used as new 'Zernike turbulences'. We show that the turbulence internal process that allows the decomposition has a high correlation with a phase distortion based on a single Zernike polynomial or a combination of them. [ABSTRACT FROM AUTHOR]

A side channel pump is a pump with a high head and a small flow that is widely used in various industrial fields. Many scientists have studied the hydraulic performance, pressure fluctuation characteristics, and gas-liquid mixed transport characteristics of this type of pump. However, these studies mainly focused on the single-stage impeller of the side channel pump, without considering the inter-stage connection channel and the multistage timing effect. These characteristics affect the hydraulic performance and pressure-pulsation characteristics of the side channel pump. Therefore, we carried out a numerical simulation and an experimental comparison on the multistage side channel pump to explore its flow characteristics during the stages. This study focused on the influence of different turbulence models on the numerical simulation of multistage side channel pumps. Shear stress transport (SST), detached eddy simulation (DES), and detached eddy simulation-curvature correction (DES-CC) turbulence models were selected for consideration. By studying the pressure and velocity streamline distribution, the turbulent kinetic energy, and the shape and volume of the vortex core area simulated by the three models, we concluded that the DES-CC model, when compared to the other models, can more fully reflect the vortex characteristics and the simulation results that are closer to the experimental data. The results of this study can be used as the basis for future research on multistage side channel pumps. [ABSTRACT FROM AUTHOR]

Flows in river habitats are characterized by unsteady turbulence due to the existence of woody debris, boulders and vegetation. As a representative aquatic species, fish is important for the riverine ecosystems, with its complex behavioural responses to turbulent flows. Previous studies investigated the fish–vortices interaction with vortex streets by placing objects with simplified geometries centred at the flow. Nonetheless, complex river morphology in natural rivers results in much more spatially heterogeneous flows due to randomly distributed obstructions. Thus, a semi‐circular cylinder patch located on one side of the flume is used to mimic a vegetation patch at the riverbank. The patch varies in diameter (D0 = 16, 20 and 24 cm) and density (φ = 0.04 and 0.1), whereas the flow velocity is fixed at 25 cm s−1. Fish are observed to swim in three typical patterns, which are "swim around" (pattern 1), "spill" (pattern 2) and "swim through" (pattern 3). For flow with a dense patch, all three patterns are recorded, but only patterns 1 and 2 are observed in sparse patches. It is noticed that in patterns 1 and 2, fish prefer to hold place in zones of low velocity and low turbulence. Moreover, variations in patch diameter have little influence on pattern selection. Results showed that tail beat amplitude (TBA*) in each zone displayed more variations compared with tail beat frequency (TBF). In addition, Spearman's rank tests revealed that TBA* is affected by none of the four hydrodynamic variables (U,ustd,τxy,Ωz), whereas flow velocity imposes the most influence on TBF. Both diameter and density of the patch displayed no significant influence on TBA* and TBF. [ABSTRACT FROM AUTHOR]

This paper presents the method of the turbulent flow simulation. The method may be used to address the computational aeroacoustics (CAA) problems, where the vortex noise’s sources have to be determined. This method is an alternative to both large-eddy simulation (LES) methods and stochastics turbulence simulation techniques. The proposed method is more computationally efficient compared to LES and, unlike stochastic approaches, it does not require empirical constants. The simulation according to this method is achieved in two main stages. During the first step the averaged flow’s properties are obtained using the RANS simulation. These properties are used for the formulation of the discrete vortex model on the second step. Vortices’ intensities are oscillating with amplitudes and frequencies obtained from the RANS simulation with random phase shifts. Turbulent velocity field is then determined as the sum of averaged flow velocities, velocities induced by the pulsing vortices and velocities induced by the trailing vortices (Kelvin circulation theorem). The method is verified by considering the test problem. The developed turbulent boundary layer near the horizontal wall is simulated by means of both the presented method and the LES method. A good agreement between these two methods indicates on the viability of the approach presented in this paper. However, a thorough investigation of the method is still yet to be accomplished.

In this study, micro jets were applied to actively controlling the flow of the international standard ducted propeller model. The detached-eddy simulation (DES) method with the shear stress transport (SST) k ‐ ω turbulence model was adopted for numerical simulation. Three ways of installing injectors and three jet flow velocities were considered. It was found that for all installation ways, injecting the jets improves the hydrodynamic efficiency when the jets are set at the two lower velocities. The maximum improvement of 3.8% was obtained from the two-injector installation with the medium jet velocity that is two times the freestream velocity. The micro jets disturb vortices developed from the blade tips and hub, and the disturbance aggregates the breakdown of these vortices. The micro jets trigger additional vortices at the duct leading edge, which become secondary vortices aside the helical blade-tip vortices. This effect was also found for the baseline model, but it is much weaker. The angle of attack of the blade is changed accordingly, which leads to the increasing of both thrust and torque. However, the hydrodynamic efficiency is increased, since the power consumed by the torque increment is smaller than that for the thrust increment. • Micro jets were applied innovatively to actively controlling the flow of the international standard ducted propeller model. • The 3-D structure of wake vortices and overall efficiency under different jets conditions were discussed comprehensively. • The maximum increase of overall efficiency, 3.8%, was found when the number and jets ratio of injector are both two. [ABSTRACT FROM AUTHOR]

The effects of a Trapped Vortex Cavity (TVC) on the aerodynamic performance of a NACA 0024 airfoil at a constant angle of attack (AoA) of 14° were investigated in this study. It was observed that mass suction (MFR) was required to stabilise the vortex within the cavity segment. Lift to drag ratio (L/D) and MFR were chosen as performance objectives, along with a fully attached flow constraint (flow separation at X/c ≥ 95% ). Parametric analysis was carried on the baseline airfoil with and without suction and compared to the airfoil with TVC with and without suction. It was observed that L/D increases as MFR increases for a baseline airfoil, and flow separation is delayed at high suction values (MFR = 0.2 kg/s). The TVC modifies the pressure distribution on the baseline airfoil when MFR is applied to the cavity section and there is a significant increase in lift; thus, L/D increases and flow separation is delayed. A lower value of MFR = 0.08 kg/s is sufficient to stabilise the vortex and improve the efficiency of the TVC airfoil. The findings of these parametric studies were used to do a multi-objective optimisation using a genetic algorithm to attain the desired cavity shape while achieving the largest L/D and the lowest MFR (that is proportional to the power required for control) with a fully attached flow constraint. It was found that mass suction and cavity shape both had an equal influence on flow control. The Pareto optimal front yielded a series of optimum designs. One of them was subjected to an off-design analysis in order to validate its performance at other incidences. It was observed that it performs better than the baseline airfoil, with an improved L/D and an increase in stall angle from 10° to 14°. [ABSTRACT FROM AUTHOR]

The instability of surface lenticular vortices is investigated using a comprehensive suite of laboratory experiments combined with numerical linear stability analysis as well as nonlinear numerical simulations in a two-layer Rotating ShallowWater model. The development of instabilities is discussed and compared between the different methods. The linear stability analysis allows for a clear description of the origin of the instability observed in both the laboratory experiments and numerical simulations. While global qualitative agreement is found, some discrepancies are observed and discussed. Our study highlights that the sensitivity of the instability outcome is related to the initial condition and the lower-layer flow. The inhibition or even suppression of some unstable modes may be explained in terms of the lower-layer potential vorticity profile. [ABSTRACT FROM AUTHOR]

The application of a synthetic jet actuator in workplaces entails the necessity of noise reduction, which they generate. One of the methods to achieve this is the use of the chevron orifice or nozzle. Therefore, the impact of different numbers of chevrons and rounding of cutouts in the orifice on the actuator efficiency and the sound pressure level was tested. The chevron orifices were compared to the circular orifice. The time-mean reaction force method was used to measured efficiency and flow parameters, and the noise was measured according to the ISO 3746:2010. The rounded cutouts had an advantageous impact on the actuator efficiency at the power P > 1   W , while the efficiency of the actuator with classic chevron orifice was smaller than with circular orifice. The noise generated by the actuator with the chevron orifice was smaller from 0.6 to 1.6 dB than by the actuator with the circular orifice, at the number of chevrons equal to 7 or more. The rounding of cutouts in the chevron orifice can advantageously impact the parameters of synthetic jet actuators. [ABSTRACT FROM AUTHOR]

The Liutex vector is new quantity introduced to represent the rigid-body rotation part of fluid motion and thus to define and identify vortices in various flows. In this work, the intermittency and power-law similarity of the Liutex vector in homogeneous, isotropic turbulence and a turbulent channel are explored. First, we found that the Liutex vector is more intermittent than the vorticity vector in the considered turbulent flows, which indicates that an iso-surface of a Liutex magnitude with an appropriate threshold could capture the major rotating motions or vortical motions of the flow. Second, the three-dimensional energy spectrums of velocity, vorticity (enstrophy spectrum) and the Liutex vector in homogeneous isotropic turbulence are shown to exhibit power laws of −5/3, 1/3 and 1/3 in the inertial subrange, respectively, whilst the Liutex energy spectrum particularly satisfies an additional −10/3 power law in the viscous subrange. This viscous similarity of the Liutex vector is the only power law that survived from the wall presence and is argued to originate from the fact that the Liutex vector represents the rigid part of fluid motion and is free from any shear contamination. The existence of such a viscous similarity law indicates a certain coherence of the small scales of turbulence and could possibly help understand and model turbulence.

Heat transport in rotating processes finds a wide range of application in which academic issues in the fluid mechanics and heat transfer areas are here reported. This paper discusses successive works from the seminal paper of Taylor (1923) to recent numerical results established from a broad range of methods such as DNS, LES, RANS or LB methods. The flow regimes identification is thus reported in Taylor–Couette geometry. The role of the axial flow rates in the apparition, stabilization and destruction of the large-scale of the turbulent structures is depicted in the case of Taylor–Couette–Poiseuille geometry. In a non-isothermal condition, a discussion is held on the various exponent values found in the scaling relationships relying on the Nusselt number as a function of the Rayleigh or Reynolds numbers according to the regimes of thermal convection.

In study, flow structures around buildings placed triple-diagonal and 7.5 cm and 10 cm distances between buildings with dimensions of 5cmx5cmx5cm without roof were investigated as experimental by using Particle Image Velocimetry (PIV) technique. Besides, flow analysis vicinity one building without roof as numerical with ANSYS Fluent program having steady, three dimensional, k-ε turbulence model was done and the attained results were matched with these of experimental. In the work, distributions of streamline <ψ> and velocity vectors were drawn and average equivalent velocity curves were researched for different distances between buildings. It was determined that jet flow region fairly enlarged at 10 cm distance according to distance of 7.5 cm and flow separation area around building placed as diagonal shrank. However, it was found that there is at most a 3% differences between experimental and numerical results. [ABSTRACT FROM AUTHOR]

The use of a chevron nozzle/orifice is one of the methods of heat transfer enhancement and noise reduction. In the case of synthetic jets, the number of papers on this topic is small. Therefore, a synthetic jet actuator with three different chevron orifices and one circular orifice is investigated. The aim of this study is to find the impact of orifice shape on centerline velocity (measured with a hot-wire anemometer) and determine if the chevron orifice reduces the generated noise. The sound pressure level was strongly dependent on the input actuator's power, and only one chevron orifice ensured noise reduction for low power (p = 6; 8 W). At real power p = 12 W, the sound pressure level was lower for each chevron orifice actuator than in the case of the circular orifice actuator. It is shown that the application of a chevron nozzle does not have to provide noise reduction. It is important in the case of the design of new actuators that are to operate in places where noise levels should be limited (e.g., offices). [ABSTRACT FROM AUTHOR]

Unsteady cavitating turbulent flow around a NACA66 hydrofoil was simulated using a mass transfer cavitation model and a modified filter-based turbulence model in this paper. The modified filter-based turbulence model can accurately predict the pressure coefficient in midplane and shedding frequency of the unsteady cloud cavitation than standard κ – 𝜀 model and filter-based turbulence model. The time evolution of transient cavitation cloud structure predicted by the three-turbulence model was compared. The result which was predicted by the modified filter-based turbulence model is in good agreement with the experimental results. The time evolution of re-entrant jet had been analyzed. The instantaneous wall-pressure evolution on the suction surface (SS) predicted by the modified filter-based turbulence model had been analyzed. The cavitation-vortex interaction had been analyzed in this study. The different effects on the cavitation-vortex interaction of the vortex stretching term, vortex dilatation term and baroclinic torque term in the transport equation of vorticity had been discussed. [ABSTRACT FROM AUTHOR]

In a healthy human cardiac system, a large asymmetric clockwise vortex present in the left ventricle (LV) efficiently diverts the filling jet from the mitral annulus to the left ventricular outflow track. However, prior clinical studies have shown that artificial mitral valve replacement can affect the formation of physiological vortex, resulting in overall flow instability in the LV. Lately, the findings from several recent hemodynamic studies seem to suggest that the native D‐shaped mitral annulus might be a crucial factor in the development of this physiological flow pattern, with its inherent flow stability and formation of coherent structures within the LV. This study aims to investigate the effect of orifice shape and its position with respect to the posterior wall of the ventricle on vortical formation and turbulence intensity in the LV, by utilizing four separate orifice configurations within an in vitro left heart simulator. Stereo particle image velocimetry experiments were then carried out to characterize the downstream flow field of each configuration. Our findings demonstrate that the generation of the physiological left ventricular vortical flow was not solely dependent upon the orifice shape but rather the subsequent jet‐wall interaction. The distance of the orifice geometric center from the left ventricular posterior wall plays a significant role in this jet‐wall interaction, and thus, vortical flow dynamics. [ABSTRACT FROM AUTHOR]

A micro-electromechanical resonator, consisting of a 125 × 125 μ m 2 center plate suspended 2 μ m above a substrate, was immersed in 4 He along with a quartz tuning fork. The tuning fork was placed 5 mm above the resonator and was used to generate turbulence. The damping of the resonator was investigated in the presence of turbulence generated by the tuning fork. We observe a velocity, v c ≃ 5 mm s - 1 , above which the damping on the resonator is drastically reduced for all tuning fork velocities studied. We attribute this change in damping to the shedding and capture of vortices. [ABSTRACT FROM AUTHOR]

This paper aims to present a multifractal approach of the turbulent atmosphere, by proposing that it can be considered a complex system whose structural units support dynamics on continuous but non-differentiable multifractal curves. Implementing the theoretical framework of multifractality through non-differentiable functions in the form of scale relativity theory with arbitrary and constant fractal dimension, the minimal vortex of an instance of turbulent flow is considered. The results of this assumption lead to an equation that describes the minimal vortex itself, and the velocity fields that compose it, the vortex and turbulent energy dissipation derived from the vortex being plotted and studied. With its structure mathematically described, while employing a classical dynamical turbulence model and relations between turbulent energy dissipation and the minimal vortex, relations are then extrapolated to allow for the solving of multiple turbulent parameters using the inner and outer length scales of the turbulent flow. These equations are then solved as altitude profiles with the necessary length scales obtained from processing lidar data. Finally, profiles are taken periodically and assembled into timeseries, in order to exemplify the method and to compare the results with known literature.

The application of a synthetic jet actuator in workplaces entails the necessity of noise reduction, which they generate. One of the methods to achieve this is the use of the chevron orifice or nozzle. Therefore, the impact of different numbers of chevrons and rounding of cutouts in the orifice on the actuator efficiency and the sound pressure level was tested. The chevron orifices were compared to the circular orifice. The time-mean reaction force method was used to measured efficiency and flow parameters, and the noise was measured according to the ISO 3746:2010. The rounded cutouts had an advantageous impact on the actuator efficiency at the power P>1 W, while the efficiency of the actuator with classic chevron orifice was smaller than with circular orifice. The noise generated by the actuator with the chevron orifice was smaller from 0.6 to 1.6 dB than by the actuator with the circular orifice, at the number of chevrons equal to 7 or more. The rounding of cutouts in the chevron orifice can advantageously impact the parameters of synthetic jet actuators.

To analyze the accuracy and differences of diverse turbulence models in predicting the flow around baffles of self-designed wet dust treatment system, several representative Reynolds Averaged Navier-Stokes (RANS) models of Standard κ-ε, RNG κ-ε, SST κ-ω and RSM were selected to simulate the vortex flow induced by arc baffles respectively, and the simulation result was also compared with experiment data. The simulation parameters mainly include the vortex structure, pressure distribution and velocity distribution, and the results show that all the simulations based on the four turbulence models can roughly describe the main characteristics of the vortex flow around baffles, while the Standard κ-ε and RNG κ-ε modes are more accurate. For the pressure drop and total pressure distribution, the results of Standard κ-ε model deviate from the other models, and the decreasing sequence of predicted values is Standard κ-ε，RNG κ-ε，RSM and SST κ-ω. The predicted results of RNG κ-ε model for longitudinal velocity are the closest to the experiment data, while the accuracy of SST κ-ω model for predicting near wall flow and lateral velocity is relatively high. [ABSTRACT FROM AUTHOR]

In this work, large eddy simulation combined with volume of fluid method is performed to simulate the flow and the associated vortices in a pump sump. The numerical results are compared with experimental data. Particular interest is paid to discovering the temporal evolution of the free-surface and floor-attached vortices. Both vortices undergo periodic enhancement and attenuation due to the advection and stretching/tilting effects generated by the background flow. The primary vortex core is accompanied by spirally wrapped secondary vortex tubes, resulting in anisotropic turbulence structure around the vortex core regions. The findings provide a deep insight into the application of large eddy simulation in pump sump and the underlying mechanism of vortex formation and evolution in the sump. [ABSTRACT FROM AUTHOR]

In this paper, the effects of regular waves propagating against the current on the wake of a wide bathymetric obstacle are experimentally investigated. For that purpose, a square cylinder of height representing 1 / 8 t h of the water column, mounted perpendicular to the flow, is used. Both Reynolds and Froude numbers are close to the ones encountered at sea and swell properties (amplitude, frequency and wavelength) which are typical conditions in the English Channel. To study this complex hydrodynamic interaction, PIV measurements are used to capture the velocity field around and in the wake of the cylinder. The wake of this wide cylinder has been extensively studied and is characterised by its direction towards the water surface and by energetic and wide vortices arising from the sheared layer at a Strouhal number of approximatively 0.06, after a merging of smaller eddies. In this work, the focus is on how surface gravity waves, propagating against the current, modify the generation of these turbulent structures. The results show that the cylinder wake is strongly modified in the presence of waves, even if, on average, the main wake structure is globally conserved. The waves act both on the vortex generation and the wake development with modifications in terms of turbulent energy distribution and level, wake recovery and ascent rate. The vortex shedding becomes highly energetic and well-organised from the cylinder position. Its return period is extremely regular and corresponds to half of the wave frequency which is really close to the natural vortex shedding frequency. That results in a doubling of the statistical length scale of the vortices. • Swell induced-motion effects on high and isolated bathymetry roughness. • Bottom mounted cylinder wake characterisation in presence of waves opposing current. • Vortex generation and dynamic study. • Energy transfer between wave and vortex shedding frequency in the near-wake. [ABSTRACT FROM AUTHOR]

With the increasing application of bidirectional axial pump, it is necessary to study the flow and cavitation characteristics of bidirectional pump. In this paper, the cavitation and flow characteristics of the tip clearance under different clearances and different cavitation numbers of the S-hydrofoil bidirectional axial flow pump were studied by combining experimental and numerical simulation methods under reverse operation conditions. The section of the bidirectional pump was experimentally studied by high-speed photography and pressure pulsation. Based on the method of RANS, the SST-CC turbulence model and ZGB cavitation model were used to simulate the clearance cavitation of the bidirectional pump, and the cavitation morphology, velocity distribution, clearance vortex structure and energy distribution of blade tip clearance were investigated. The study reveals the flow characteristics of the clearance flow field of the bidirectional pump, and provides reference for the design and operation of it. • Deep cavitation bidirectional pump gap tail will form reverse shear cavitation. • Special distribution of S-shaped hydrofoil gap velocity will form a variety of vortices. • More disorderly flow field at the tail of the bidirectional pump gap. [ABSTRACT FROM AUTHOR]

This paper shall present a multifractal interpretation of turbulent atmospheric entities, considering them a complex system whose dynamics are manifested on continuous yet non-differentiable multifractal curves. By bringing forth theoretical considerations regarding multifractal structures through non-differentiable functions in the form of an adaptation of scale relativity theory, the minimal vortex of an instance of turbulent flow is considered. In this manner, the spontaneous breaking of scale invariance becomes a mechanism for atmospheric turbulence generation. This then leads to a general equation for the non-differentiable vortex itself, with its component velocity fields, and to a vortex turbulent energy dissipation—all of which are plotted and studied. Once the structure of the non-differentiable multifractal structure is mathematically described, an improved phenomenological turbulence model and relations between turbulent energy dissipation and the minimal vortex are employed together, exemplifying the codependency of such models. Using turbulent medium wave propagation theory, certain relations are then extrapolated which allow the obtaining of the inner and outer length scales of the turbulent flow using lidar data. Finally, these altitude profiles are compiled and assembled into timeseries to exemplify the theory and to compare the results with known literature. This model is a generalization of our recent results published under the title “On a Multifractal Approach of Turbulent Atmosphere Dynamics”.

The use of a chevron nozzle/orifice is one of the methods of heat transfer enhancement and noise reduction. In the case of synthetic jets, the number of papers on this topic is small. Therefore, a synthetic jet actuator with three different chevron orifices and one circular orifice is investigated. The aim of this study is to find the impact of orifice shape on centerline velocity (measured with a hot-wire anemometer) and determine if the chevron orifice reduces the generated noise. The sound pressure level was strongly dependent on the input actuator’s power, and only one chevron orifice ensured noise reduction for low power (p = 6; 8 W). At real power p = 12 W, the sound pressure level was lower for each chevron orifice actuator than in the case of the circular orifice actuator. It is shown that the application of a chevron nozzle does not have to provide noise reduction. It is important in the case of the design of new actuators that are to operate in places where noise levels should be limited (e.g., offices).