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The study of gas transport in low-permeability rocks is both practical and of significant importance to produce tight rock reservoirs. The presence of nanopores in tight rocks results in distinctly different gas transport mechanisms from those found in conventional reservoirs. Traditional Darcy's law is inadequate for describing gas flow in this context. Instead, various modes of gas transport, such as continuum flow, slip flow, transition flow, and Knudsen diffusion for bulk gas, as well as surface diffusion and adsorption/desorption for adsorbed gas, coexist within these nanopores. This paper mainly focuses on studies of gas transport in nanopores that consider apparent permeability. To begin with, the pore structure characteristics and gas seepage mechanisms in shale are introduced. An overview of the three main methods for measuring apparent permeability including laboratory experiments, numerical simulations, and analytical techniques, is provided. Mathematical models describing gas transport within nanopores are emphasized as a foundational component of apparent permeability measurements. Furthermore, the factors that influence these models are discussed. Upon analyzing the existing models, it is evident that they are diverse and numerous. While these models typically encompass multiple mechanisms and influencing factors related to gas transportation, each model has its specific limitations. Therefore, there is a continued need for the development of more comprehensive and general models. This study offers the most detailed overview of gas transport mechanisms and mathematical models in low-permeability rocks, aiming to support the evaluation and exploitation of tight rock reservoirs. [ABSTRACT FROM AUTHOR]

Identification of suitable polymeric materials to fabricate microneedles (MNs) for the collection of interstitial fluid (ISF) is a challenge. Here, characterization of different carrageenan‐biopolymer composites for MN patch fabrication intended for ISF collection is reported. Systematic oscillatory rheological studies of composites containing iota‐carrageenan mixed with alginate, gelatin, or pectin are performed to determine the linear viscoelastic region, gel point, tan delta, complex viscosity, and flow transition index. A polynomial equation is derived by relating flow transition index of biopolymer composites and compression strength of fabricated MNs. The biopolymer composite of iota‐carrageenan and gelatin at 2% and 14%, respectively, and CaCl2 crosslinker (80 mm) shows the greatest compression strength sufficient for MNs insertion into the excised porcine skin. MNs swell up on application in an agarose gel model and the ex vivo excised porcine skin model to collect 36 ± 5 and 14 ± 1 µL of fluid within 10 min, respectively. Taken together, it is demonstrated that rheological analysis can be performed to select suitable polymer composites that possess sufficient strength for the skin insertion and swellability for ISF collection. [ABSTRACT FROM AUTHOR]

In recent years, leading-edge tubercles have gained significant attention as an innovative biomimetic flow control technique. This paper explores their impact on the aerodynamic performance and flow patterns of an airfoil through wind tunnel experiments, utilizing force measurements and tuft visualization at Reynolds numbers between 2.7 × 105 and 6.3 × 105. The baseline airfoil exhibits a hysteresis loop near the stall angle, with sharp changes in lift coefficient during variations in the angle of attack (AOA). In contrast, the airfoil with leading-edge tubercles demonstrates a smoother stall process and enhanced post-stall performance, though its pre-stall performance is slightly reduced. The study identifies four distinct flow regimes on the modified airfoil, corresponding to different segments of the lift coefficient curve. As the AOA increases, the flow transitions through stages of full attachment, trailing-edge separation, and local leading-edge separation across some or all valley sections. Additionally, the study suggests that normalizing aerodynamic performance based on the valley section chord length is more effective, supporting the idea that leading-edge tubercles function like a series of delta wings in front of a straight-leading-edge wing. These insights provide valuable guidance for the design of blades with leading-edge tubercles in applications such as wind and tidal turbines. [ABSTRACT FROM AUTHOR]

In this work, the physiochemical properties of the drug, isoproterenol hydrochloride, were analyzed in the presence of β-cyclodextrin in an aqueous medium to gain a better understanding of the prevailing interactions among solute–solvent systems with the help of viscosity and conductivity studies. From viscosity measurements, the viscosity B -coefficient along with its transfer parameter was calculated using the Jones–Dole equation. In addition to this, the activation parameters such as Δ μ 1 o # , Δ μ 2 o # , Δ S 2 o # , and Δ H 2 o # were evaluated and discussed to gain a better understanding of the mechanism of viscous flow in terms of transition state theory. Along with this, conductivity studies were performed to investigate the thermodynamics of the ternary system in terms of changes in Gibbs free energy. Also, the delayed critical aggregate concentration of the ternary system supports favourable interaction between the studied drug and β-cyclodextrin molecules. [ABSTRACT FROM AUTHOR]

Flexible contact gasket is a significant component affecting the sealing performance of the refrigerator. However, few studies were conducted on the permeability characteristics of moist air through refrigerator gaskets. The purpose of this study is to explore the permeability characteristics including permeation paths size, flow type, modeling and temperature-humidity-pressure-structure effect. The characteristic scale of the interface of permeation paths is observed as 10−5 m in the free-state by atomic force microscope. The equation of Knudsen number and contact stress relation is established to judgment the flow types. By comparing the critical and simulated contact stresses, it is inferred that moist air simultaneously occurs slip, transition and free-molecular flows. A multi-scale coupling model of permeation rate is constructed to obtain the apparent permeability coefficient characterizing the permeability intensity. The air pressure difference affects the permeability characteristics in the form of direct driving force and changing the contact stress of the interfaces. Free-molecular flow mainly occurs under the negative pressure condition with inhalation coefficient of 2.26 × 10−5∼2.84 × 10−5 m2, while the slip flow mainly occurs under the positive pressure conditions with exhalation coefficient of 2.87 × 10−5∼4.65 × 10−5 m2. The essence of enhancing the sealing performance of structural improvement is to increase the contact stress and length of permeation path. By increasing the height, increasing the inclination angle, adding the auxiliary edges and adding an auxiliary airbag, the inhalation coefficient of moist air, the exhalation coefficient of moist air and the inhalation coefficient of water vapor are decreased by 54.82 %, 51.46 % and 66.04 %. [ABSTRACT FROM AUTHOR]

Microchannel condensers play an essential role in cryogenic two-phase heat management systems due to their efficient heat transfer characteristics. Thus, it is worth conducting an in-depth study on microscale condensation characteristics of cryogenic fluids. This paper delves into the flow condensation process of methane in microchannels. A two-dimensional transient model with high accuracy for cryogenic fluids has been developed by combining a self-defined program for the source term of the phase transition model. The model fully considers the boundary layer thickness and accurately explores the mesh accuracy. The complete condensation flow patterns are captured for various vapor quality, mass flux, and wall subcooling degrees. The injection flow is a unique flow regime for condensation in microchannels. The decrease in wall subcooling degree and increase in mass flux leads to the separation point at the neck of the injected flow moving towards the exit, while the annular flow region is expanding and the flow pattern transition is lagging. The mass flux improves the heat transfer coefficient more significantly at high vapor quality. During injection and bubble flow, the wall shear stress and local heat transfer coefficient are subject to bouncing and oscillations, which may induce fluctuations in the upstream annular flow. The prediction performance of six classical heat transfer correlations is evaluated. The results indicate that the Nie et al. correlation has the highest comprehensive prediction accuracy with MRD and MARD of -5.00 % and 15.83 %, respectively. [ABSTRACT FROM AUTHOR]

The shear flow and solid–liquid transition of mixed milk protein dispersions with varying concentrations of casein micelles (CMs) and serum proteins (SPs) are integral to key dairy processing operations, including microfiltration, ultrafiltration, diafiltration, and concentration–evaporation. However, the rheological behavior of these dispersions has not been sufficiently studied. In the present work, dispersions of CMs and SPs with total protein weight fractions (ωPR) of 0.021–0.28 and SP to total protein weight ratios (RSP) of 0.066–0.214 and 1 were prepared by dispersing the respective protein isolates in the permeate from skim milk ultrafiltration and then further concentrated via osmotic compression. The partition of SPs between the CMs and the dispersion medium was assessed by measuring the dry matter content and viscosity of the dispersion medium after separating it from the CMs via ultracentrifugation. The rheological properties were studied at 20 °C via shear rheometry, and the sol–gel transition was characterized via oscillatory measurements. No absorption of SPs by CMs was observed in dispersions with ωPR = 0.083–0.126, regardless of the RSP. For dispersions of SPs with ωPR ≤ 0.21, as well as the dispersion medium of mixed dispersions with ωPR = 0.083–0.126, the high shear- rate-limiting viscosity was described using Lee's equation with an SP voluminosity (vSP) of 2.09 mL·g−1. For the mixed dispersions with a CM volume fraction of φCM ≤ 0.37, the relative high shear-rate-limiting viscosity was described using Lee's equation with a CM voluminosity (vCM) of 4.15 mL·g−1 and a vSP of 2.09 mL·g−1, regardless of the RSP. For the mixed dispersions with φCM > 0.55, the relative viscosity increased significantly with an increasing RSP (this was explained by an increase in repulsion between CMs). However, the sol–gel transition was independent of the RSP and was observed at φCM ≈ 0.65. [ABSTRACT FROM AUTHOR]

The influence of silo width on dense granular flow in a two‐dimensional silo is investigated through experiments and simulations. Though the flow rate remains stable for larger silo widths, a slight reduction in silo width results in a significant increase in flow rate for smaller silo widths. Both Beverloo's and Janda's formula accurately capture the relationship between the flow rate and outlet size. Flow characteristics in the regions near the outlet exhibit local self‐similarity, supporting Beverloo and Janda's principles. Moreover, global self‐similarity is analyzed, indicated by the transition in flow state from mass flow in regions far from the outlet to funnel flow near the outlet. The earlier occurrence of this transition favors to enhance the grain velocity and consequently increases the dense flow rate. An exponential scaling law is proposed to describe the dependencies of flow rate, grain velocity, and transition height on silo width. [ABSTRACT FROM AUTHOR]

Vehicles equipped with advanced driving assistance systems (ADAS) can acquire information about preceding and following vehicles, which will have an undeniable impact on the phase transition of traffic flow. Therefore, we establish a new heterogeneous continuum model of traffic flow considering the jerk effect mixed with human driving (HD) and ADAS vehicles. The neutral stability condition associated with the permeability of ADAS vehicle is inferred via stability analysis. According to simulation, shock wave occurs, implying that our model can emerge correct wave propagation trend. Moreover, the simulation of density evolution and flow changes also suggests that an increase in ADAS vehicle penetration and jerk effect can enhance traffic system stability and reduce energy consumption. [ABSTRACT FROM AUTHOR]

The upgrading of existing systems in industries, along with the limited space for modern equipment, often requires engineers to arrange thermal systems in inclined or vertical positions. Changing the orientation of heat exchangers can have significant consequences, such as higher pumping costs and reduced performance. The present experimental assessment focuses on the influence of inclination angles, heat flux, and geometrical parameters of inlet flaps on heat transfer and fluid flow characteristics inside a solar air heater. The Reynolds number varies from 494 to 6965. Experiments are carried out with two heat fluxes, 0.5 and 1 kW/m2. The geometric configuration of a rectangular inlet flap is characterized by two nondimensional parameters: height ratio (h = 0.75, 0.50, and 0.25) and width ratio (w = 0.25, 0.20, and 0.15). For a plain tube with a 15° inclination and 1 kW/m2 of applied heat flux, the transition initiates at a Reynolds number of 2666 and terminates at a Reynolds number of 4025. For a plain tube with a 30° inclination, the range of critical Reynolds numbers is between 2764 and 4139. With the inlet flap barrier under similar operating conditions, the transition starts and ends earlier than in the plain tube. Additionally, a significant increase in the Nusselt number and friction factor is observed when the inlet flap is placed in the channel. At 15°, the transition begins earlier, while at 30° inclination, the transition is slightly delayed. Novel correlations for the Nusselt number and friction factor are developed to predict heat transfer and pressure drop for unknown parameters. [ABSTRACT FROM AUTHOR]

Based on a diesel hydrogenation unit in Middle East, INPLANT software is for hydraulic calculations of the two-phase flow pipeline in the reaction system. The effects of pipeline diameter, gas-liquid ratio and fluid load on the transition of two-phase flow patterns in horizontal pipelines are analyzed. The results show that the unsteady slug flow can be transformed into stable annular flow by increasing the gas-liquid ratio of the fluid; changing the pipe diameter and fluid load cannot transform the two-phase flow pattern of the pipeline studied in this paper from slug flow to annular flow; however, when the liquid phase velocity is reduced to a sufficiently low, the flow pattern can be transformed into wavy flow. The calculation results are used to guide the operation adjustment of the unit, improving the gas-liquid ratio of the fluid can eliminate the pressure fluctuations of the reaction system. It shows that the flow pattern transformation trend simulated by the software is close to the actual production, and the accuracy is high. [ABSTRACT FROM AUTHOR]

Heat transfer and pressure drop in laminar and turbulent flow have been studied for a long time. However, the thermohydraulic of fluid flow in transition flow is still in the embryonic stage and needs further exploration. Primarily, this article complied all the fragmented research works linked to thermal and flow performance in transition-flow regimes. Several detailed research works pertaining to developing and fully developed transition flow were reported in the past three decades which significantly contribute to the field. It was also found that the transition-flow regime shifted with the change in the operating conditions such as free, forced and mixed convection, developing and fully developed flow, inlet geometries, type of working fluid, channel geometries, roughness, the orientation of test section, etc. Hence, by altering the shape of the entrance, the amount of heat passing through, or the surface of the tube, one could manipulate the range of Reynolds numbers where the transition took place. The temperature of fluids affects their densities, so when heat is applied to the tube wall, it creates temperature differences within the thermal boundary layer. These differences in temperature then cause changes in density and buoyancy due to the force of gravity. Several novel correlations have been developed based on these findings to determine the heat transfer and pressure drop in different flow regimes. In order to develop accurate correlations for heat transfer and pressure drop in the transitional-flow regime, it is necessary to comprehend the factors that impact the beginning and end of this regime. This understanding is crucial for selecting or creating suitable correlations. [ABSTRACT FROM AUTHOR]

To investigate the characteristics of the bi-stable flow at subcritical Reynolds numbers, large eddy simulation is adopted to simulate the crossflow around two tandem circular cylinders at Re = 3900. The reattachment/co-shedding bi-stability is observed in the simulations with spacing ratios (L/D, L is the center-to-center cylinder spacing and D is the diameter) of 4.5 and 4.7. Statistical analyses are performed on the hydrodynamic coefficients, time-averaged flow fields, three-dimensional characteristics, wake pattern, and vortex shedding frequencies at different spacing ratio and time period. In addition, a detailed analysis and explanation were conducted on the secondary vortices identified in the reattachment flow regime, revealing that the secondary vortices, generated from the instability of the shear layer, significantly influence the variation in vortex shedding frequency over time. The reduced-order variational mode decomposition method is employed to decompose the flow field during the flow regime transitions, unveiling their spatial and temporal features. It is revealed that the shear layer instability and the low-frequency modulation behavior are the predominant factors triggering the bi-stable phenomenon at subcritical Reynolds numbers. This study aims to uncover triggering mechanisms underlying the bi-stable phenomenon in the flow around two tandem cylinders and provides valuable insight for relevant engineering applications. [ABSTRACT FROM AUTHOR]

Accurately identifying the onset of transitional and turbulent flow within any pipe flow environment is of great interest. Most often, the critical Reynolds number (Re) is used to pinpoint the onset of turbulence. However, the critical Re is known to be highly variable, depending on the specifics of the flow system. Thus, for flows (e.g., blood flows), where only one realization (i.e., one mean Re) exists, the presence of transitional and turbulent flow behaviors cannot be accurately determined. In this work, we aim to address this by evaluating the extent to which instantaneous time-frequency (TF)-based analysis of the fluctuating velocity field can be used to evaluate the onset of transitional and turbulent flow regimes. Because current TF analysis methods are not suitable for this, we propose a novel "wavelet-Hilbert time-frequency" (WHTF) method, which we validate herein. Using the WHTF method, we analyzed the instantaneous dominant frequency of three planar particle image velocimetry-captured pipe flows, which included one steady and two pulsatile with Womersley numbers of 4 and 12. For each case, data were captured at Re's spanning 800–4500. The instantaneous dominant frequency analysis of these flows revealed that the magnitude, size, and coherence of two-dimensional spatial frequency structures were uniquely different across flow regimes. Specifically, the transitional regime maintained the most coherent, but lowest magnitude frequency structures, while the laminar regime had the highest magnitude, lowest coherence, and smallest frequency structures. Overall, this study demonstrates the efficacy of TF-based metrics for characterizing the progression of transition and turbulent flow development. [ABSTRACT FROM AUTHOR]

Receptivity is the focus and frontier of the research on boundary layer transition and flow drag reduction, but the temporal and spatial evolution of Tollmien–Schlichting waves (T-S waves) is not yet fully investigated, limiting the development of highly efficient laminar flow control techniques. In the present study, the local receptivity problem of the laminar boundary layer on a zero-pressure-gradient flat plate is investigated by using the direct numerical simulation, considering both the temporal and spatial evolution characteristics of the T-S waves. External disturbances at fixed frequencies are introduced in the form of velocity pulsations with different periods to excite T-S waves. The temporal and spatial evolution characteristics of the T-S waves excited by different forms and periods of disturbances are studied. It is found that the amplitude, frequency, and wave velocity of the T-S wave induced by the external multi-period disturbances are different from those induced by the constant disturbances. These conclusions are the same as those of T-S wave induced by wall inhalation. After a further investigation on this particular phenomenon, the influence mechanism of external disturbances on the receptivity process is revealed. This new research finding enriches the instability theory and provides a reference for more efficient applications on active laminar flow control technologies. [ABSTRACT FROM AUTHOR]

Detecting the flow regimes of Newtonian turbulence (NT), elasto-inertial filament (EIF), elasto-inertial turbulence (EIT), and maximum drag reduction (MDR) of polymer solution and their transition has been a hot topic in the last decade. We attempted to detect NT, EIF, EIT, and MDR by visualizing vortex shedding downstream of an array of cylinders that was inserted perpendicular to polymer-doped two-dimensional (2D) flow. Since polymers are stretched at the cylinders, the consequent vortex shedding is affected by viscoelasticity. The flow regimes are characterized based on Weissenberg (Wi) and Reynolds numbers (Re) with the relaxation time of the polymeric solution estimated from capillary-thinning experiments. The flow regimes are observed for different molecular weights of polyethylene oxide and polyacrylamide in solution and are categorized as either vortex type 1, type 2, and type 3 on a Re–Wi map based on flow visualization using particle image velocimetry. In addition, turbulent statistics of these flow regimes are calculated to more fully quantify these flow regimes. We found that vortex types from 1 to 3 have a similarity to NT, EIF, EIT, and MDR. In addition, characteristic turbulent energy transfer without an increase in turbulent energy production was found in the flow regimes of vortex types 2 and 3 of each polymer solution. Our results suggest intriguing parallels between pipe, jet, and 2D turbulent flow for drag-reducing polymeric solutions. [ABSTRACT FROM AUTHOR]

The study of the complex rheological properties of viscoelastic fluids in nanochannels will facilitate the application of nanofluidics in biomedical and other fields. However, the flow of viscoelastic fluids in nanochannels has significant instabilities, and numerical simulation failures are prone to occur at high Weissenberg numbers (Wi). In this study, the simplified Phan-Thien-Tanner viscoelastic fluid model is solved using the log-conformation tensor approach, and the effects of rheological parameters of the viscoelastic fluid, such as the Weissenberg number (Wi), extensibility parameter (ε), and viscosity ratio (β), on the flow characteristics and flow instability within the nanochannel are investigated. The results indicate that the variation of rheological parameters of viscoelastic fluids has a significant effect on the flow state and flow instability of fluids in nanochannels. When the rheological parameters are in a specific range, the flow velocity and outlet current in the nanochannel exhibit relatively regular periodic fluctuations. As the flow transitions from an up-and-down moving single-vortex state to a symmetric double-vortex state, the average velocity of the central axis in the nanochannel is increased by about 15%. Furthermore, when Wi increases from 150 to 400, the length and height of the vortex increase by 50% and 100%, respectively. [ABSTRACT FROM AUTHOR]

In this work, we numerically investigate how a nonuniform magnetic field affects the flow and heat transfer in a bottom-heated closed enclosure filled with a thermosensitive ferrofluid. Under the simultaneous action of the gravitational and external magnetic field, a complex flow develops inside the cavity. We change the intensity of the external magnetic field aiming to understand how the flow field, temperature distribution, and net heat transfer are affected. Our findings reveal that the magnetic field has a significant influence on the topology of the flow and temperature fields, consequently impacting the overall heat transfer. It is possible to use the magnetic field generated by a conducting wire to change the net heat transfer through the cavity. We found that the average Nusselt number is a growing function of the magnetic field intensity, except for a specific Rayleigh number. Furthermore, we recognize non-stationary regimes at intermediate magnetic Rayleigh numbers, associated with unstable topological transitions in the flow pattern induced by the magnetic field. Consequently, we uncover flow regimes characterized by steady boundary conditions but exhibiting periodic flow and heat transfer patterns. Additionally, we observe that the unsteady topological transitions are suppressed by high magnetic Rayleigh numbers, resulting in steady flow. [ABSTRACT FROM AUTHOR]

Local continuity is established for locally bounded, weak solutions to a doubly non-linear parabolic equation that models the temperature of a material undergoing a multi-phase transition. The enthalpy, as a maximal monotone graph of the temperature, is allowed to possess several jumps and/or infinite derivatives at the transition temperatures. The effect of the p-Laplacian-type diffusion is also considered. As an application, we demonstrate a continuity result for the saturation in the flow of two immiscible fluids through a porous medium, when irreducible saturation is present. [ABSTRACT FROM AUTHOR]

Numerical modeling of gas flows in rarefied regimes is crucial in understanding fluid behavior in microscale applications. Rarefied regimes are characterized by a decrease in molecular collisions, and they lead to unusual phenomena such as gas phase separation, which is not acknowledged in hydrodynamic equations. In this work, numerical investigation of miscible gaseous mixtures in the rarefied regime is performed using a modified lattice Boltzmann model. Slip boundary conditions are adapted to arbitrary geometries. A ray-tracing algorithm-based wall function is implemented to model the non-equilibrium effects in the transition flow regime. The molecular free flow defined by the Knudsen diffusion coefficient is integrated through an effective and asymmetrical binary diffusion coefficient. The numerical model is validated with mass flow measurements through microchannels of different cross-section shapes from the near-continuum to the transition regimes, and gas phase separation is studied within a staggered arrangement of spheres. The influence of porosity and mixture composition on the gas separation effect are analyzed. Numerical results highlight the increase in the degree of gas phase separation with the rarefaction rate and the molecular mass ratio. The various simulations also indicate that geometrical features in porous media have a greater impact on gaseous mixtures' effective permeability at highly rarefied regimes. Finally, a permeability enhancement factor based on the lightest species of the gaseous mixture is derived. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the nonlinear dynamics of convection flow using the thermodynamic variational principle, focusing on scenarios where multiple external forces, such as a thermal gradient and rotational field, are applied to a shallow annular pool. We observed that with the increase in the thermal gradient, the flow changed from an axial flow to a rotational oscillatory flow with the wave amplitudes aligned. Further increasing the temperature difference led to a rotational oscillatory flow characterized by alternating wave generation and annihilation. Our analysis of the flow, considering heat fluxes orthogonal to the thermal gradient, allowed us to describe the flow state as a phase at equilibrium. The state transition of the flow was accompanied by a discontinuous jump in the heat flux, which occurred at the intersection of the entropy production curves. The first transition occurred at a temperature difference Δ T = 12.4   K   M a r a n g o n i   n u m b e r , M a = 1716 and the second at ΔT = 16.3 K M a = 2255 . Analysis based on entropy production could accurately predict the observed transition points. [ABSTRACT FROM AUTHOR]

The rapid melting of glaciers and thawing of permafrost in mountainous regions have heightened the danger of rock‐ice avalanches. These avalanches pose a severe threat due to their potential to transform into water‐saturated debris flows. The catastrophic event in Chamoli, India, on 7 February 2021, illustrates the devastating consequences of such processes. Developing a model capable of predicting the dynamics and extent of these events is imperative for natural hazard science and disaster mitigation. In response, we propose a depth‐averaged rock‐ice avalanche model encompassing four distinct materials: rock, ice, snow, and water. The model integrates crucial physical processes, including frictional heating, phase changes, ground material entrainment, and air‐blast hazards. Through a system of mass and momentum balance equations extended with grain flow and internal energy equations, the model captures heat exchanges and resulting phase changes as the fragmented material flows. Focusing on identifying the primary water source in the flow and testing the model on the 2021 Chamoli event, we quantify water's influence on flow dynamics and regime transitions. However, uncertainties persist in heat transfer physics and quantifying the hydro‐meteorological state of the flow path. Our thermo‐mechanical model enables the simulation of complex avalanches and identifies key flow transitions: powder cloud formation and potential debris flow transformation. The study underscores the pivotal role of water in avalanche dynamics and the challenge of accurately quantifying water content within the flow, necessitating comprehensive ground assessments for effective disaster management. Plain Language Summary: In the context of global climate warming, the rapid melting of glaciers and thawing of permafrost lead to rock and ice mass collapses, forming rock‐ice avalanches. These can evolve into water‐saturated debris flows, increasingly endangering societies and infrastructures in hazard‐prone regions. The 2021 Chamoli rock‐ice avalanche, which transformed into a debris flow causing over 200 fatalities, exemplifies the severe consequences of such natural disasters. To address this issue, we developed a depth‐averaged model to predict the complex dynamics characteristics of rock‐ice events. The model considers various components like rock, ice, snow, and water, along with crucial processes such as frictional heating, phase changes, material entrainment, and air‐blast hazards; and captures heat changes between phases and resultant phase transitions. Using this model, we investigated the primary water source within avalanche flows and its effects on dynamics, focusing on the 2021 Chamoli avalanche. Our findings highlight the pivotal role of water in shaping the behavior of these rock‐ice events and flow transitions. Despite significant progress, challenges remain in refining our understanding of heat transfer physics and quantifying hydro‐meteorological conditions within the flow. Nevertheless, our thermo‐mechanical model represents a significant advancement in simulating and comprehensively analyzing the dynamics of rock‐ice avalanches. Key Points: New depth‐averaged model for rock‐ice avalanches, including rock, ice, snow, and water, phases changes, ground entrainment and air blastOur model identifies three key flow transitions: powder cloud formation, debris flow transformation, and hyperconcentrated flood occurrenceModel testing shows water's impact on flow transitions. Uncertainties remain in heat transfer and entrainment calling for more validation [ABSTRACT FROM AUTHOR]

The liquid–liquid immiscible flow and mass transfer were investigated in a novel Taylor–Couette microreactor (TCMR). Due to the rotation shear and microscale effects, each phase flowed in the form of helical strips/bands, instead of dispersion droplets as in conventional equipment. Based on the movement and inclination of the bands, the helical vortex (HV), mixed helical vortex (MHV) and stationary helical vortex (SHV) were distinguished. The characteristics of the regimes were strongly influenced by rotation speed and flow rate, but the specific surface area only slightly varied. The flow regimes also influenced the two phase mass transfer. It was shown that the mass transfer coefficient kLa monotonically increased with the rotation speed in the HV regime, while it slightly decreased when the flow shifted into the MHV/SHV regime. According to the parametric studies, empirical correlations were developed for the flow regime transition and mass transfer prediction. [ABSTRACT FROM AUTHOR]

2D materials provide an ideal platform to explore novel superconducting behavior including Ising superconductivity, topological superconductivity and Majorana bound states in different 2D stoichiometric Ta‐, Nb‐, and Fe‐based crystals. However, tuning the element content in 2D compounds for regulating their superconductivity has not been realized. In this work, the synthesis of high quality Fe1+yTe with tunable Fe content by chemical vapor deposition (CVD) is reported. The quality and composition of Fe1+yTe are characterized by Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). The superconducting behavior of Fe1+yTe crystals with varying Fe contents is observed. The superconducting transition of selected Fe1.13±0.06Te sample is sharp (ΔTc = 1 K), while Fe1.43±0.07Te with a high‐Fe content shows a relative broad superconducting transition (ΔTc = 2.6 K) at zero magnetic field. Significantly, the conspicuous vortex flow and a transition from a 3D vortex liquid state to a 2D vortex liquid state is observed in Fe1.43±0.07Te sample. This work highlights the tunability of the superconducting properties of Fe1+yTe and sheds light on the vortex dynamics in Fe‐based superconductors, which facilitates them to understand the intrinsic mechanisms of high‐temperature superconductivity. [ABSTRACT FROM AUTHOR]

This study investigates the three-dimensional (3D) wake transition in unconfined flows over rectangular cylinders using direct numerical simulation (DNS). Two different cross-sectional aspect ratios (AR) and Reynolds numbers (Re) are scrutinized: AR = 0.5 at Re = 200 and AR = 3 at Re = 600. The investigation focuses on characterizing the flow patterns and forecasting their temporal evolution utilizing the proper orthogonal decomposition (POD) technique coupled with a long short-term memory (LSTM) network. The DNS results reveal the emergence of an ordered mode A for AR = 3, attributed to the stabilizing effect of the elongated AR. On the other hand, the case with a smaller AR (= 0.5) exhibits a mode-swapping regime characterized by modes A and B's distinct and simultaneous manifestation. The spanwise wavelengths of mode A and mode B are approximately 4.7 and 1.2 D for AR = 0.5, while the spanwise wavelength of mode A is 3.5 D for AR = 3. The POD serves as a dimensionality reduction technique, and LSTM facilitates temporal prediction. This algorithm demonstrates satisfactory performance in predicting the flow patterns, including the instabilities of modes A and B, across both transverse and spanwise directions. The employed algorithm adeptly predicts the pressure time series surrounding the cylinders. The duration for training the algorithm is only about 0.5% of the time required for DNS computations. This research, for the first time, demonstrates the effectiveness of the POD–LSTM algorithm in predicting complex 3D instantaneous wake transition patterns for flow past rectangular cylinders. [ABSTRACT FROM AUTHOR]

In recent years, the flow-induced vibration and noise in automotive refrigerant system gradually become the main factor affecting driving comfort. However, the relationship of flow pattern, vibration, and noise is not clear, and pattern identification is not easy but necessary. In this paper, a series of experiments are conducted to investigate the relationship of flow pattern, flow-induce vibration, and noise near the thermal expansion valve in an automobile refrigerant system. The flow pattern, vibration, and noise are closely related to startup processes. Mist flow, which contains more mist two-phase mixture than transition flow and wispy-annular flow, leads to the largest amplitude of vibration and strong broadband hiss noise. Moreover, the increase in compressor speed promotes the pattern transition and the vibration amplitude in time domain but has no effect on the distribution of vibration peaks in frequency spectrum. Finally, a short-time Fourier transform and convolutional neural network combined method for flow pattern identification is developed based on the relationship of flow pattern and flow-induced noise. After using transfer learning and data augmentation, four trained network architectures show relatively high accuracy above 94% for test set. Among them, ResNet34 not only has the highest accuracy of 98.8% but also can recognize each type of flow pattern. The generalization of this method can help engineers to recognize flow patterns in air conditioning without flow visualization but only need to measure sound signals. [ABSTRACT FROM AUTHOR]

Direct numerical simulations are performed to investigate the flow past a transversely rotating sphere confined in a pipe. Three sphere diameters of d = 0.2 D , 0.5 D , and 0.8 D (D is the pipe diameter) and sphere Reynolds numbers (based on the sphere cross-sectional mean velocity and d) of R e s = 250 – 500 are considered. The simulation results highlight the combined effects of the blockage ratio (BR = d / D) and the nondimensionalized rotation rate Ω in the range of 0.2–1.2 on the wake flow. For each BR , with increasing R e s and Ω , the wake flow undergoes a transition of the flow pattern from steady symmetry and unsteady symmetry to unsteady asymmetry. For BR = 0.2 , the variation in flow behaviors with Ω is similar to those reported in the previous studies on a transversely rotating sphere subjected to a uniform flow. With increasing BR from 0.2 to 0.5, the unsteady asymmetric wake flow is characterized by distorted near-wake vortex rings and a series of staggered inward rolled-up vortex arcs on the double streamwise vortex threads, which results in a low-frequency modulation of the unsteady wake flow. These rolled-up vortex arcs are connected with downstream quasi-streamwise vortices and form hairpin-like vortices. Dynamic Mode Decomposition (DMD) analysis shows that the distorted near-wake vortex rings are associated with the antisymmetric DMD mode at the adjacent frequency around the symmetric primary DMD mode. With BR = 0.8 , there is a drastic increase in the sphere's force coefficients. A more complex wake flow behavior is found due to a strong interaction between the wake flow and the near-pipe-wall flow. At Ω = 1.2 , dominant asymmetric flow structures are characterized by impingement of the vortex filaments. The low-frequency modulation of these wake structures is also analyzed using the DMD analysis. [ABSTRACT FROM AUTHOR]

The behavior of a three-dimensional, non-Brownian flexible filament in a low Reynolds number shear flow was investigated through theoretical and numerical analyses. In the phase plane with Reynolds number R e ∈ [ 0.03 , 8 ] and flow intensity Z ∈ [ 800 , 35 000 ] , four primary motion modes of the filament were identified: rigid, C-buckling, U-turn, and S-turn. By employing the principle of symmetry, a theoretical model was developed to explain the S-turn mode, and we discovered that the critical flow strength for the transition from U-turn to S-turn was approximately Z c = 4900. Our numerical simulations confirmed this transition value. In a system devoid of thermal fluctuations, it was observed that the mode transitions of microscale filament precisely corresponded to the abrupt scale rate changes in the non-Newtonian behavior of the macroscopic solution. Although the polymer stress under different modes has distinct underlying causes, they can all be predicted by the generalized Hooke's law. [ABSTRACT FROM AUTHOR]

The application of data-driven methods to study cavitation flow provides insights into the underlying mechanisms and richer physical details of cavitation phenomena. This paper aims to analyze the physically interpretable multi-state cavitation behavior. Initially, the spatiotemporal features of the cavitation flow are represented as network trajectories using principal component analysis. The k-means++ algorithm is then employed to obtain coarse-grained flow field states, and the centroid of each cluster served as a representative for the attributes of that state. Subsequently, the Markov state model is constructed to capture the dynamic transitions in the cavitation flow field. Through a detailed analysis of the dynamic transition model, the cavitation flow field states with genuine physical mechanisms are refined. Finally, proper orthogonal decomposition (POD) is utilized to extract the flow patterns corresponding to different states. The distribution characteristics of the flow field modes in different states correspond to their physical properties. These data-driven algorithm enables a detailed analysis of the typical states in periodic cavitation processes, such as cavity growth, development, shedding, and collapse, providing a deeper understanding of the cavitation flow characteristics in different typical states. [ABSTRACT FROM AUTHOR]

The Lucas–Washburn (L-W) equation does not accurately describe capillary flow in graphene-based nanoslits, particularly in terms of channel width dependence. In this study, the dynamics of imbibition in nanoslits are explored using many-body dissipative particle dynamics across various channel widths. For smooth channel walls like those of graphene, the impact of channel width on the imbibition rate varies oppositely between narrower and wider channels. A local minimum in imbibition rate is observed, indicating decreased rates in narrower channels and increased rates in wider ones, across various wettabilities. Conversely, for rough channel walls, where wall slippage is absent, the L-W equation holds, and the imbibition rate increases linearly with channel width. This discrepancy is attributed to wall slippage on smooth surfaces, with the slip length found to increase with channel width before approaching an asymptotic value. For narrower nanoslits with smooth walls, the dynamic contact angle (CA) derived from the L-W equation with a slip condition can be less than the static CA, challenging the prevailing understanding. This "effective" dynamic CA does not accurately represent the meniscus at the liquid front but instead suggests enhanced surface wettability. [ABSTRACT FROM AUTHOR]

Stepped spillways are spillways provided by steps that are used to dissipate energy and reduce the scour and erosion that occur at the end of the hydraulic structures. Since the spillway is one of the parts of the dam used to get rid of excess water during floods, spillways can be constructed in various forms and sizes depending on the geology of the dam site and the hydraulic conditions of the flow. The stepped type was chosen because it dissipates energy and reduces the size of the basin at the end of the structure. The aim of the research is to review most of the studies that dealt with the subject of stepped spillways as energy dissipaters. This study collected much research on stepped spillways, some of which used physical models and others numerical models. These studies were performed to determine energy dissipation, flow properties, or type of flow in the stepped spillways and to study the effect of the shape of the steps on energy dissipation. The results showed that some studies indicated that when the flow over the stepped spillways is in the form of jet or free flow, it increases the efficiency of energy dissipation and reduces the length of the hydraulic jump. It is worth mentioning that some studies used software such as ANSYS, while others used artificial intelligence (AI) techniques like genetic programming and fuzzy logic. [ABSTRACT FROM AUTHOR]

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This study aims to investigate the wake of two tandem square cylinders based on the Proper Orthogonal Decomposition (POD) analyses of the PIV and hotwire data. The cylinder centre-to-centre spacing ratio L/w examined is from 1.2 to 4.2, covering the four flow regimes, i.e., extended body, reattachment, transition and co-shedding. The Reynolds number examined was 1.3 × 104. A novel Proper Orthogonal Decomposition (POD) technique (hereafter referred to as PODHW) is developed to analyse data from single point hotwire measurements, offering a new perspective compared to the conventional POD analysis (PODPIV) based on Particle Image Velocimetry (PIV) data. A key finding is the identification of two distinct states, reattachment and co-shedding, within the transition flow regime at L/w = 2.8, which PODPIV fails to capture due to the limited duration of the PIV data obtained. This study confirms, for the first time, the existence of these states as proposed by Zhou et al. (2024), highlighting the advantage of using PODHW for capturing intermittent flow phenomena. Furthermore, the analysis reveals how the predominant coherent structures contribute to the total fluctuating velocity energy in each individual regime. Other aspects of the flow are also discussed, including the Strouhal numbers, the contribution to the total fluctuating energy of the flow from the first four POD modes, and a comparison between different regimes. [ABSTRACT FROM AUTHOR]

Global climate change has been intensifying the scale and frequency of rock‐ice avalanches and similar catastrophic mass movements in high‐mountain regions. The difference in the physical characteristics of rock and ice particles leads to mixing and segregation during flow. Although, both particle segregation and the presence of ice fundamentally alter flow behavior, the joint influence and feedback of these two aspects are overlooked in state‐of‐the‐art rock‐ice avalanche models. Using discrete element simulations, we show that by controlling the distribution of inter‐particle frictional interactions within the mixture, segregation patterns resulting from the size, density, concentration, and surface friction differences of rock and ice phases can induce sharp velocity gradients along the flowing thickness. Flowing layers where low friction contacts with ice are abundant tend to flow faster and can induce slow creeping motion in an otherwise static basal layer dominated by more frictional rocks. Based on these observations, we find that the effective friction of rock‐ice flows for various mixture concentrations and size ratios can be obtained as a sum of the single‐phase rheologies of rocks and ice weighted according to their microscopic contact probabilities. This effective friction for rock‐ice mixtures allows us to extend a recent non‐local granular fluidity framework that captures the complex segregation‐flow feedback mechanism in rock‐ice flows. The findings provide a deeper micromechanical understanding of how particle interactions influence rock‐ice avalanche mobility, which ultimately improves flow models needed for hazard assessment and mitigation. Plain Language Summary: Rock‐ice avalanches are hazardous mass flows in alpine regions. Being granular in nature, the difference in the size, concentration, density, and surface roughness of rock and ice particles can drive them to segregate. However, the segregation of rocks and ice and its impacts on the bulk flow dynamics are overlooked in current rock‐ice avalanche models. Using granular flow simulations, we show that size and density segregation, coupled with the surface friction difference between the rocks and ice, can induce sharp transitions in the avalanche flow velocity by controlling the probabilities in which rocks and ice contact with each other. This study highlights the importance of microscopic frictional interactions in modeling the flow resistance of rock‐ice mixtures, and the enhanced understanding presented here may further improve rock‐ice avalanche modeling necessary for hazard management. Key Points: Vertical segregation coupled with large friction differences results in sharp transitions in the flow profiles of rock‐ice avalanchesThe rheology of rock‐ice mixtures is governed by the interparticle contact probabilitiesSharply varying flow profiles are modeled using the granular fluidity model incorporating the dependence on contact probabilities [ABSTRACT FROM AUTHOR]

The investigation of frictional pressure drops in wire-wrapped bundles at low flow velocities is crucial for thermal-hydraulic studies of sodium-cooled fast reactor cores. This study aims to refine empirical formulas for predicting friction factors in wire-wrapped bundles by addressing their limitations in accurately calculating friction factors during transition regime. By analyzing existing empirical formulas and meticulously observing frictional pressure drop experiments conducted under low-flow conditions that reported in the literature, the study proposes and demonstrates the mechanism of the laminar-to-transitional regime transition in wire-wrapped bundles. Additionally, experimental research was conducted on the frictional pressure drop of a 37-rod wire-wrapped bundle. A novel high-precision differential pressure measurement technique, the photographic liquid column manometer, was employed to enhance frictional pressure drop measurement accuracy. This innovative method achieves a measurement uncertainty of less than 2 Pa within a range of 0 to 300 Pa. The mass flow rate of the fluid was measured and converted to obtain the flow velocity through the assembly, further improving the accuracy of flow velocity measurements. The analysis and experiments reveal that the transition from the laminar to transitional regime does not occur uniformly but initiates locally in certain subchannels before spreading across the assembly as flow velocity increases. Significant increases in the frictional pressure drop occur only after a sufficient number of subchannels have undergone transition. This perspective is supported by extensive existing literature, which report that in assemblies with fewer rod bundles, smaller P/D and H/D values, and constructed from hard metal materials such as stainless steel, the friction factor at the initial stage of the transitional regime shows a significant increase or remains constant with increasing Reynolds number. Under these conditions, the high consistency of the P/D ratio within the assembly causes the fluid to transition within a narrow range of flow velocities, leading to a marked increase in the friction factor with Reynolds number. The research results also indicate that the prediction accuracy of the critical Reynolds number for the laminar-to-transitional flow transition significantly impacts the calculation accuracy of empirical formulas at low flow velocities. Formulas using smaller predicted values of the critical Reynolds number show better agreement between predicted values and the measured results in this study. Therefore, the study recommends adopting smaller critical Reynolds numbers and interpolation indices in empirical formulas to facilitate an early onset and smooth transition of laminar-to-transitional regime behavior in friction factors, thereby improving the accuracy of calculated friction factors.

Background: Patients with hypoplastic left heart syndrome undergo the comprehensive stage 2 procedure as the second stage in the hybrid approach toward Fontan circulation. The complexity of comprehensive stage 2 procedure is considered a potential limitation, and limited information is available on its anesthetic management. This study aims to address this gap. Methods: A single‐center retrospective cohort study analyzed 148 HLHS patients who underwent comprehensive stage 2 procedure, divided into Group A (stable condition, n = 116) and Group B (requiring preoperative intravenous inotropic therapy, n = 32). Demographic data, intraoperative hemodynamics, anesthetic management, and postoperative outcomes were collected. Results: Etomidate (40%) was the most common induction agent, followed by esketamine (24%), midazolam (16%), and propofol (13%). Inhaled induction was rarely necessary (2%), occurring only in Group A patients. No statistical differences were found between groups for induction drug choice. Post‐cardiopulmonary bypass management included moderate hypoventilation, inhaled nitric oxide (100%), and hemodynamic support with milrinone (97%) and norepinephrine (77%). Group B patients more frequently required additional levosimendan (20%) and epinephrine (18%). Extracorporeal membrane oxygenation was necessary in 8 patients (5%) with no between‐group differences. Switching from fentanyl to remifentanil reduced postoperative ventilation time overall. However, Group B experienced significantly longer ventilation (6.3 vs. 3.5 h) and ICU stay (22 vs. 14 days). In‐hospital mortality was 5% overall (Group A: 4%, Group B: 9%). Long‐term survival analysis revealed a significant advantage for Group A. Conclusion: The use of short‐acting opioids and adjusted ventilation modes enables optimal pulmonary blood flow and rapid transition to spontaneous breathing. Differentiated hemodynamic support with milrinone, norepinephrine, supplemented by levosimendan and epinephrine in high‐risk patients, can mitigate the effects on the preoperatively volume‐loaded right ventricle. However, differences in long‐term survival probability were observed between groups. Trial Registration: Local ethics committee, Medical Faculty, Justus‐Liebig‐University‐Giessen (Trial Code Number: 216/14). [ABSTRACT FROM AUTHOR]

The effect of a novel ribbed wave tape on the augmentation of heat transfer in a solar air heater operating in a transitional flow regime is experimentally examined. Three different wave ratios are used, and the tube is uniformly heated using heat fluxes while the Reynolds number varied from 521 to 10,194. The transition for plain tube begins at 2810 and ends at 3724. For tube with ribbed wavy tapes, transition begins early and ends at higher Reynolds number than plain tube. For 2 kW/m2 of heat flux, the transition for wavy tape having wave ratio 3 begins at Reynolds number 2589 while at heat flux of 4 kW/m2, the transition begins at Reynolds number 2745. The end of transition takes place at Reynolds number 3969 and 4139 for wave ratio 3 at heat fluxes 2 and 4 kW/m2, respectively. The length of transition decreases with increase in the wave ratio at uniform heat flux. The average enhancement in Nusselt number for ribbed wavy tapes having wave ratio 3 at 4 kW/m2 heat flux was 262% and 85% for laminar and turbulent flow regime, respectively. Two empirical correlations were developed to predict the Nusselt number and friction factor for all the flow regimes. [ABSTRACT FROM AUTHOR]

The flow regime in geology is critical to the underground activity. In this study, axial seepage tests within a wide range of grain sizes were conducted to better understand the influence of pore size distribution and pore structure evolution on hydraulic characteristics in porous media. The effect of pore size distribution and evolution on flow regime transition was quantitatively analyzed. The pore size distribution was controlled by varying uniformity coefficient (Cu) (4 < Cu < 24) and curvature coefficient (Cc) (0.2 < Cc < 14). The results show that coefficient size appears to have a positive correlation with the permeability of the granular materials, but cannot impact the transition of flow regime that is mainly dominated by the heterogeneity of the pore structure. Compared to the pore space and the effect of medium, the heterogeneity of pore structure significantly impacts on the occurrence of pre-Darcy flow and directly correlates with the magnitude of inertial forces or fluid velocity. It demonstrates that the curvature coefficient (Cc) is an important characteristic parameter in flow transition. The particle size ratio d 60 d 30 could be considered as one of the reference characteristic particle sizes for assessing non-Darcy flow characteristics. Subjected to the axial stress, the critical hydraulic gradient for the transition from pre-Darcy to post-Darcy flow was reduced, and even the pre-Darcy flow disappeared. These findings will contribute to the identification of non-Darcy flow transition in groundwater and promote a better understanding of the nonlinear evolution behavior of fluids under underground extraction conditions. [ABSTRACT FROM AUTHOR]

This paper studies the instability of a non-ideal pipe system conveying fluid. Unlike ideal modeling, three types of possible non-ideal factors have been considered in the present analysis. The pipe has a crack and is subjected to boundary relaxation, and the fluid in the pipe is viscous. It is an interesting instability problem of a fluid-structure system with multiple forms of imperfections. It gains motivation from our previous study and aims at further essential results for comprehensively understanding the nature of such a problem. In order to incorporate multiple imperfections, a new data-driven approach is developed to model the non-ideal pipe-fluid system. Then the influences of the support stiffness, fluid–solid mass ratio, crack, and fluid viscosity on the pipe instability are systematically discussed. Results show that the pipe exhibits flutter-divergence conversion at low mass ratios and flutter-mode transition at high mass ratios. Due to the two types of instability transitions, the critical flow speed could experience multiple sudden jumps as the support stiffness changes. With the imperfections of crack and viscous flow, the pipe's instability behavior tends to be more complicated, but the inducing mechanisms for the sudden changes are straightforward. They are instability-type conversion, instability-mode transition, and laminar-turbulent flow transition. [ABSTRACT FROM AUTHOR]

Gaseous hydrogen is commonly stored under high pressures due to its low volumetric storage density. The safety concerns about its release and potential accidents, such as vapour cloud explosions, were of the highest importance in industries. This research work established a methodology for consequence analysis of compressed hydrogen releases, considering various stages of event escalation, including high-pressure gas release, gas jet dispersion, and overpressure evaluations. Specifically, compressed hydrogen release was defined as an under-expanded flow, characterised by a transition from sonic to supersonic velocities. The notional nozzle theory was employed to tackle the flow regime transition and provide revised nozzle size and gas velocity as inputs to the CFD model for gas jet dispersion. The model was validated against experimental results, exhibiting a good agreement with a deviation of less than 20%. The flammable gas mass in the cloud was determined using the dispersion model and then used for overpressure predictions. This approach proved to be more realistic than relying solely on the total hydrogen release amount. In a case study, release parameters such as release direction, wind speed and release hole size were investigated. It was observed that a downward release resulted in less gas dissipation, leading to larger overpressures compared to other release directions. Wind speed had a relatively lower impact compared to other parameters. The release hole size had the most significant influence on explosion overpressure, with the case of a larger release size (e.g., 50.8 mm) exhibiting a few hundred times higher of hazardous area compared to a small hole size (e.g., 3 mm). • Modelling approach for high-pressure H 2 release is developed. • Release direction and nozzle size significantly impact the consequence of H 2 release. • Methodology can be used for consequence analysis in risk assessment. [ABSTRACT FROM AUTHOR]

The Zhongsha Platform is the largest modern isolated carbonate platform of around 8600 km2 in the South China Sea, providing a unique case study for sedimentary processes in pure carbonate settings. High-resolution multibeam bathymetric data, two-dimensional seismic profiles, and surface sediment cores are utilizes to reveal the initiation and evolution of submarine canyons on the northeastern slope of the Zhongsha Platform. Three submarine canyons are revealed within the survey area that incise the slope at water depths between 600 and 4100 m. C1 presents a linear pattern, whereas C2 and C3 exhibit dendritic morphologies. A large-scale scalloped collapse has deeply excavated the platform margin and slope. Within this catastrophic failure, C2 originated in a northeastward orientation and subsequently converted to an eastward direction with a length of 54.8 km. It is distinguished by the erosion of numerous tributaries in the upper course, the transition of flow direction in the middle course, and the presence of retrogressive landslides in the lower course. Slope landslides extend eastward from middle-lower slope towards the oceanic basin at water depths ranging from 2300 to 4200 m. A series of scarps and immature canyons have developed with escarpments showing pronounced relief at the landslide heads. The triggering mechanisms of platform margin collapses and slope landslides are attributed to sediment aggradation, slope oversteepening, gravity flows, relative sea-level changes, surface monsoon currents, and deep cyclonic circulation. The canyon evolution is explained through four stages: Inception stage, sediment instability on platform margin and slope-toe; Expansion stage, the presence of platformmargin collapses and slope landslides; Development stage, the initiation of submarine canyons eroded by gravity flows with downslope and retrogressive erosion; Present stage, the upper slope canyon incised into the landslide area and ultimately integrated with the lower slope canyon, creating an elongated modern canyon. This work contributes to enhance our understanding of the detailed morphology, transport processes, and triggering mechanisms of submarine canyons in the pure carbonate systems. [ABSTRACT FROM AUTHOR]

To date, a comprehensive understanding of the influence of the Prandtl number ($Pr$) on flow topology in turbulent Rayleigh–Bénard convection (RBC) remains elusive. In this study, we present an experimental investigation into the evolution of flow topology in quasi-two-dimensional turbulent RBC with $7.0 \leq Pr \leq 244.2$ and $2.03\times 10^{8} \leq Ra \leq 2.81\times 10^{9}$. Particle image velocimetry (PIV) measurements reveal the flow transitions from multiple-roll state to single-roll state with increasing $Ra$ , and the transition is hindered with increasing $Pr$ , i.e. the transitional Rayleigh number $Ra_t$ increases with $Pr$. We mapped out a phase diagram on the flow topology change on $Ra$ and $Pr$ , and identified the scaling of $Ra_t$ on $Pr$ : $Ra_t \sim Pr^{0.93}$ in the low $Pr$ range, and $Ra_t \sim Pr^{3.3}$ in the high $Pr$ range. The scaling in the low $Pr$ range is consistent with the model of balance of energy dissipation time and plume travel time that we proposed in our previous study, while the scaling in the high $Pr$ range implies a new governing mechanism. For the first time, the scaling of $Re$ on $Ra$ and $Pr$ is acquired through full-field PIV velocity measurement, $Re \sim Ra^{0.63}\,Pr^{-0.87}$. We also propose that increasing horizontal velocity promotes the formation of the large-scale circulation (LSC), especially for the high $Pr$ case. Our proposal was verified by achieving LSC through introducing horizontal driving force $Ra_H$ by tilting the convection cell with a small angle. [ABSTRACT FROM AUTHOR]

Direct numerical simulations (DNS) were carried out to investigate flow control for transition delay using steady blowing/suction strips at the wall of a flared cone at Mach 6 and zero angle of attack. For the numerical investigations of the transition control strategy, the flared cone geometry and the flow conditions of the experiments in the Boeing/Air Force Office of Scientific Research (AFOSR) Mach 6 Quiet Tunnel (BAM6QT) at Purdue University were chosen. For the DNS, transition was initiated by introducing random disturbances at the inflow of the computational domain, emulating 'natural' transition in wind-tunnel experiments caused by free-stream noise. In both wind-tunnel experiments and numerical simulations, streamwise 'hot' streaks were found on the surface of the flared cone, which are caused by a nonlinear interaction of an axisymmetric second-mode wave and a pair of oblique waves of the same frequency ('fundamental resonance'). The objective of the flow control strategy proposed here is to delay the transition onset, and thus mitigate the negative consequences associated with the nonlinear transition stages, i.e. the development of hot streaks and large wall-pressure amplitudes that were observed in experiments and DNS. Our previous so-called 'controlled' transition simulations have shown that flow control using steady blowing and suction strips can lead to a significant delay of the hot streak development on the surface of the flared cone. The simulation results presented in this paper show that this flow control strategy remains effective, even in a natural transition scenario characterized by broadband disturbances. [ABSTRACT FROM AUTHOR]

Jamming is an athermal transition between flowing and rigid states in amorphous systems such as granular matter, colloidal suspensions, complex fluids and cells. The jamming transition seems to display mixed aspects of a first-order transition, evidenced by a discontinuity in the coordination number, and a second-order transition, indicated by power-law scalings and diverging lengths. Here we demonstrate that jamming is a first-order transition with quenched disorder in cyclically sheared systems with quasistatic deformations, in two and three dimensions. Based on scaling analyses, we show that fluctuations of the jamming density in finite-sized systems have important consequences on the finite-size effects of various quantities, resulting in a square relationship between disconnected and connected susceptibilities, a key signature of the first-order transition with quenched disorder. This study puts the jamming transition into the category of a broad class of transitions in disordered systems where sample-to-sample fluctuations dominate over thermal fluctuations, suggesting that the nature and behavior of the jamming transition might be better understood within the developed theoretical framework of the athermally driven random-field Ising model. Jamming in amorphous systems is an athermal transition characterized by mixed first-order and second-order aspects. Authors demonstrate that jamming is a first-order transition with quenched disorder, revealing significant finite-size effects and a square relationship between disconnected and connected susceptibilities in cyclically sheared systems. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of the flow regime transition is a prerequisite for designing and operating the rotating drum, especially when dealing with non-spherical particles. In this study, the multi-sphere method was used to construct cylindrical particles. The optimal number of spherical elements for particles with different aspect ratios was determined in terms of kinetic energy, rotational kinetic energy, collision number, collision force, deformation and angle of repose. And the effects of filling rate, rotational speed and particle size on the macro- and micro-behavior of cylindrical particles were systematically investigated. The results show that when the aspect ratio of cylindrical particle is 2, 3 and 4, the optimal number of spherical elements are 5, 8, and 10, respectively. Four flow structures, namely rolling, cascading, cataracting and centrifuging, were identified with the increase of the rotation speed, but the transition boundary from rolling to cascading is not clear due to the irregular particle shape. Three flow structures, namely slipping, transition, and cascading, were identified with the increase of the filling degree. The transition diagram of flow regime was established. The results show that the aspect ratio has a great influence on the flow transition from slipping to cascading regime. The area covered by the transition flow regime expands as the aspect ratio increases, necessitating a greater filling degree to achieve a stable rolling flow regime. [ABSTRACT FROM AUTHOR]

To investigate continental dynamics underneath the south‐central Tibetan plateau, which composes the Himalayan, Lhasa, and Qiangtang blocks, we have conducted comprehensive examinations of seismic azimuthal anisotropy in the crust using receiver functions (RFs) and crustal and mantle anisotropy using teleseismic shear wave splitting (SWS) analysis. In the Qiangtang block, the observed predominantly E‐W fast orientations from RF and SWS analyses with similar magnitude are interpreted as resulting from eastward crustal flow with minor contributions from the mantle. In the Lhasa block, the crustal anisotropy is approximately N‐S oriented, which is parallel to the strike of rift basins and southward crustal flow. Anisotropy revealed by SWS demonstrates a rotation from E‐W in the north to NE‐SW in the south, which can be interpreted as reflecting mantle flow field induced by the northward movement of the subducting Indian plate. The addition of PKS and SKKS measurements and extension of epicentral distance range to 171.8° for SWS analysis revealed dominantly strong E‐W oriented anisotropy in most parts of the Himalayan block, where most previous studies reported pervasively null measurements. The absence of azimuthal anisotropy is observed in two regions in the Himalayan block which is attributable to mantle upwelling through a previously identified slab window. A two‐layered anisotropy structure with different fast orientations for the upper and lower layers can be constrained in the southern Qiangtang and the vicinity of the Main Boundary Thrust. Plain Language Summary: In our study exploring the underground dynamics beneath the south‐central Tibetan plateau, an area encompassing the Himalayan, Lhasa, and Qiangtang blocks, we utilized advanced seismic techniques to uncover the structure and dynamics of the earth's crust and mantle. In the Qiangtang region, our findings suggest an eastward crustal movement with minimal mantle influence. In the Lhasa block, the observed crustal anisotropy aligns with rift basins with a reduced magnitude, indicating a smaller‐scale southward flow. In the same area, we also observed a transition in mantle flow patterns from east‐west in the north to northeast‐southwest in the south, attributed to the northward movement of the Indian plate. Contrary to previous studies that mostly found no anisotropy in the Himalayan block, our research detected strong anisotropy with east‐west orientations. In two areas of the Himalayan block, the absence of anisotropy likely results from molten rock rising through a gap in the Indian plate. Moreover, we discovered a two‐layered structure of rock alignment near the Main Boundary Thrust and the Qiangtang block. Key Points: Significant anisotropy is revealed in the Himalayan block, where previous studies suggest pervasively null measurementsThe crust significantly impacts observed anisotropy in teleseismic shear wave splitting, potentially leading to double‐layered anisotropyAsthenospheric upwelling through a slab window beneath the Himalayan block accounts for the pervasive null measurements [ABSTRACT FROM AUTHOR]

The intermittency characteristics in transitional and turbulent flows can provide critical information on the underlying mechanisms and dynamics. While time–frequency (TF) analysis serves as a valuable tool for assessing intermittency, existing methods suffer from resolution issues and interference artifacts in the TF representation. As a result, no suitable or accepted methods currently exist for assessing intermittency. In this work, we address this gap by presenting a novel TF method—a Fourier-decomposed wavelet-based transform—which yields improved spatial and temporal resolution by leveraging the advantages of both integral transforms and data-driven mode decomposition-based TF methods. Specifically, our method combines a Fourier-windowing component with wavelet-based transforms such as the continuous wavelet transform (CWT) and superlet transform, a super-resolution version of the CWT. Using a peak-detection algorithm, we extract the first, second, and third most dominant instantaneous frequency (IF) components of a signal. We compared the accuracy of our method to traditional TF methods using analytical signals as well as an experimental particle image velocimetry (PIV) dataset capturing transition to turbulence in pulsatile pipe flows. Error analysis with the analytical signals demonstrated that our method maintained superior resolution, accuracy, and, as a result, specificity of the instantaneous frequencies. Additionally, with the pulsatile flow dataset, we demonstrate that IF components of the fluctuating velocities extracted by our method decompose energy cascade components in the flow. Additional investigations into corresponding spatial frequency structures resulted in detailed observations of the inherent scaling mechanisms of transition in pulsatile flows. [ABSTRACT FROM AUTHOR]

This study investigates the modulating effect of the pycnocline thickness in two-dimensional stratified flow on a cylinder. It encompasses three typical flow regimes identified by Boyer in experiments conducted within the Reynolds number range of Re = 260–2000. Quantitative control of the modulation effect of internal interface waves on the cylinder wake is achieved by varying the thickness of the pycnocline. Under appropriate thickness of the pycnocline, a multiple-centerline-structure can transition to isolated-mixed-structure flow regimes and Double-Eddy-Wavy-Wake flow regimes. Similar modulation patterns are also observed in isolated-mixed flow regimes. Normalized pressure distribution and velocity fields indicate that in low Reynolds number flow regimes (Re < 600), downstream isolated mixed regions generate dynamic pressure that periodically cascades upstream. This periodic reverse energy transfer provides favorable adverse pressure gradients, cyclically reducing the drag force on the cylinder. The cyclic period is, for the first time, classified into four stages: dynamic pressure storage stage, dynamic pressure transfer stage, dynamic pressure consumption stage, and dynamic pressure exhaustion stage. Despite the highly nonlinear modulation effect of internal interface waves in low Reynolds number conditions, the linear predictive theory of lee waves based on streamline equations remains instructive in predicting the trend of lee waves wavelength variation with pycnocline thickness. Drawing upon the modulation study results concerning the pycnocline thickness on lee waves, a regime map is constructed, illustrating the directional evolution of lee waves flow patterns based on variations in pycnocline thickness. [ABSTRACT FROM AUTHOR]