The primary objective in aircraft transportation is to minimize turbulent drag, thereby conserving energy and reducing emissions. We propose a sector-shaped counter-flow dielectric barrier discharge plasma actuator, w...The primary objective in aircraft transportation is to minimize turbulent drag, thereby conserving energy and reducing emissions. We propose a sector-shaped counter-flow dielectric barrier discharge plasma actuator, which leverages jet synthesis for drag reduction. A drag control experiment was conducted in a low-speed wind tunnel with a controlled flow velocity of 9.6 m/s(Re = 1.445 × 10^(4)). This study investigated the effects of varying pulse frequencies and actuation voltages on the turbulent boundary layer. Using a hot-wire measurement system, we analyzed the pulsating and time-averaged velocity distributions within the boundary layer to evaluate the streamwise turbulent drag reduction. The results show that the local TDR decreases as the pulse frequency increases, reaching a maximum reduction of approximately 20.97% at a pulse frequency of 50 Hz. In addition, as the actuation voltage increases, the friction coefficient decreases, increasing the drag reduction rate. The maximum drag reduction of approximately 33.34% is achieved at an actuation voltage of 10 kV.展开更多
Particle-fluid two-phase flows in rock fractures and fracture networks play a pivotal role in determining the efficiency and effectiveness of hydraulic fracturing operations,a vital component in unconventional oil and...Particle-fluid two-phase flows in rock fractures and fracture networks play a pivotal role in determining the efficiency and effectiveness of hydraulic fracturing operations,a vital component in unconventional oil and gas extraction.Central to this phenomenon is the transport of proppants,tiny solid particles injected into the fractures to prevent them from closing once the injection is stopped.However,effective transport and deposition of proppant is critical in keeping fracture pathways open,especially in lowpermeability reservoirs.This review explores,then quantifies,the important role of fluid inertia and turbulent flows in governing proppant transport.While traditional models predominantly assume and then characterise flow as laminar,this may not accurately capture the complexities inherent in realworld hydraulic fracturing and proppant emplacement.Recent investigations highlight the paramount importance of fluid inertia,especially at the high Reynolds numbers typically associated with fracturing operations.Fluid inertia,often overlooked,introduces crucial forces that influence particle settling velocities,particle-particle interactions,and the eventual deposition of proppants within fractures.With their inherent eddies and transient and chaotic nature,turbulent flows introduce additional complexities to proppant transport,crucially altering proppant settling velocities and dispersion patterns.The following comprehensive survey of experimental,numerical,and analytical studies elucidates controls on the intricate dynamics of proppant transport under fluid inertia and turbulence-towards providing a holistic understanding of the current state-of-the-art,guiding future research directions,and optimising hydraulic fracturing practices.展开更多
Liquid-liquid dispersion is often performed in stirred tanks,which are valued for their ease of operation,high droplet generation rate and effective droplet dispersion.Many relevant simulations use the Eulerian-Euleri...Liquid-liquid dispersion is often performed in stirred tanks,which are valued for their ease of operation,high droplet generation rate and effective droplet dispersion.Many relevant simulations use the Eulerian-Eulerian method,combining population balance equations with statistical models to forecast droplet breakage.Conversely,the Eulerian-Lagrangian(E-L)method provides precise tracking of individual droplets,which is crucial for simulating dispersion processes.However,E-L simulation faces challenges in integrating droplet breakage effectively.To address this issue,our research introduces a probabilistic approach for droplet breakages.It assumes that a longer time increases the likelihood of breakup;a droplet breaks if the calculated probability exceeds a random value from 0 to 1.Consequently,the simulated breakage frequency becomes independent of the Lagrangian time step.The Sauter mean diameter and droplet size distribution can be accurately predicted by this probabilistic approach.By closely monitoring droplet motion,we reveal the complexity of droplet trajectories and the detailed patterns of circulation in stirred tanks.These insights contribute to a deeper understanding of liquidliquid dispersion dynamics.展开更多
This study focuses on High-Amplitude Wall Heat Flux events(HAWHFs) occurring during the interaction between a supersonic flat-plate Turbulent Boundary Layer(TBL) at a Mach number of2.25 and an oblique shock wave impin...This study focuses on High-Amplitude Wall Heat Flux events(HAWHFs) occurring during the interaction between a supersonic flat-plate Turbulent Boundary Layer(TBL) at a Mach number of2.25 and an oblique shock wave impinging at 33.2.. A database from a validated direct numerical simulation is analyzed using conditional averaging and a two-dimensional clustering methodology to elucidate the statistical characteristics of both positive and negative HAWHFs within the interaction region. The results reveal that the interaction considerably affects the temporal attributes of the HAWHFs, leading to an extended lifespan for the positive HAWHFs and an increased interval between the occurrences of negative HAWHFs. The structural characteristics of the identified HAWHFs are delineated based on the evolution of population density, aspect ratio, and both absolute and relative distances throughout the interaction. The joint probability density functions of the relative positioning of two adjacent structures indicate that, away from the reattachment point, the positive HAWHFs align in the spanwise direction, displaying similarities with the negative HAWHFs. Moreover, a conditional analysis of flow structures associated with HAWHFs is conducted. This analysis of the conditionally averaged three-dimensional fields reveals that the interaction fosters larger-scale organizational patterns in the downstream region. However, the formation of positive and negative HAWHFs remains largely unaffected by the interaction, with the former predominantly linked to a two-layer temperature structure and the latter primarily associated with a pair of oblique vortices.展开更多
In concentric annular pipes,the difference in curvature between the inner and outer wall surfaces creates significant variations in the heat transfer characteristics of the two surfaces.The simplifications of the Ditt...In concentric annular pipes,the difference in curvature between the inner and outer wall surfaces creates significant variations in the heat transfer characteristics of the two surfaces.The simplifications of the Dittus-Boelter equation for circular pipes make it unsuitable for the complex flow induced by the geometry and heat transfer coupling effects in annular pipes.This prevents it from accurately predicting the turbulent heat transfer in concentric annular pipes.This paper used realizableκ–εand low Reynolds number models to conduct numerical simulations of turbulent convective heat transfer in concentric annular pipes and circular pipes.The results indicated that the local heat transfer coefficient and Nusselt number of the inner wall surface of the annular pipe were both higher than those of the outer wall surface.The Darcy resistance coefficient decreased upon increasing the Reynolds number and increased with the inner diameter-to-outer diameter ratio.When using the equivalent diameter as the characteristic scale,the turbulent heat transfer correlation obtained from circular pipes produced significant errors when used to approximate the turbulent convective heat transfer in concentric annular pipes.This error was greater for the inner wall surface,especially when the inner and outer diameters were relatively small,as the Nusselt number error on the inner wall surface reached 60.62%.The error of the Nusselt number on the outer wall surface reached 19.51%.展开更多
The uncertainty of ocean turbulent mixing parameterization comprises a significant challenge in ocean and climate models. A depth-dependent deep learning ocean turbulent mixing parameterization scheme was proposed wit...The uncertainty of ocean turbulent mixing parameterization comprises a significant challenge in ocean and climate models. A depth-dependent deep learning ocean turbulent mixing parameterization scheme was proposed with the hydrological and microstructure observations conducted in summer 2012 in the shelf sea east of Hainan Island, in South China Sea(SCS). The deep neural network model is used and incorporates the Richardson number Ri, the normalized depth D, the horizontal velocity speed U, the shear S^(2), the stratification N^(2), and the density ρ as input parameters. Comparing to the scheme without parameter D and region division, the depth-dependent scheme improves the prediction of the turbulent kinetic energy dissipation rate ε. The correlation coefficient(r) between predicted and observed lgε increases from 0.49 to 0.62, and the root mean square error decreases from 0.56 to 0.48. Comparing to the traditional physics-driven parameterization schemes, such as the G89 and MG03, the data-driven approach achieves higher accuracy and generalization. The SHapley Additive Explanations(SHAP) framework analysis reveals the importance descending order of the input parameters as: ρ, D, U, N^(2), S^(2), and Ri in the whole depth, while D is most important in the upper and bottom boundary layers(D≤0.3&D≥0.65) and least important in middle layer(0.3<D<0.65). The research shows applicability of constructing deep learning-based ocean turbulent mixing parameterization schemes using limited observational data and well-established physical processes.展开更多
The North Water Polynya(NOW)is one of the largest and most productive polynyas in the Arctic.Compared to the surrounding sea ice,the combination of high winds and cold air,together with the thin ice or open water surf...The North Water Polynya(NOW)is one of the largest and most productive polynyas in the Arctic.Compared to the surrounding sea ice,the combination of high winds and cold air,together with the thin ice or open water surface of the NOW,produces large turbulent heat fluxes(THFs).The accurate estimation of these parameters requires high-resolution atmospheric data,which can be provided by the reanalysis products from different sources.In this study,we calculated the winter latent heat flux(LHF)and sensible heat flux(SHF)over the NOW and its surrounding sea ice area from 2005/2006 to 2015/2016 using high-resolution(15 km)Arctic System Reanalysis version 2(ASRv2)data and low-resolution(30 km)European Centre for Medium-Range Weather Forecasts ERA5 data.Results show that the LHF/SHF over the surrounding sea ice is about 82%/88%lower than over the NOW,as estimated using either dataset.Furthermore,within each area,the difference in the THFs estimated from the two datasets is small.The spatial distribution of the LHF/SHF estimated from both data sources is similar to that of sea ice concentration.The average LHF/SHF in the polynya obtained using ASRv2 data is only 5%/7%higher than that from the values obtained using ERA5 data.This is because the wind speed and air temperature from the ASRv2 data are higher than those of ERA5,and their effects on the THFs can cancel each other out.Furthermore,the estimated THFs do not necessarily improve with the refined resolution of ASRv2.展开更多
A multiscale stochastic-deterministic coupling method is proposed to investigate the complex interactions between turbulent and rarefied gas flows within a unified framework.This method intermittently integrates the g...A multiscale stochastic-deterministic coupling method is proposed to investigate the complex interactions between turbulent and rarefied gas flows within a unified framework.This method intermittently integrates the general synthetic iterative scheme with the shear stress transport turbulence model into the direct simulation Monte Carlo(DSMC)approach,enabling the simulation of gas flows across the free-molecular,transition,slip,and turbulent regimes.First,the macroscopic synthetic equations,derived directly from DSMC,are coupled with the turbulence model to establish a constitutive relation that incorporates not only turbulent and laminar transport coefficients but also higher-order terms accounting for rarefaction effects.Second,the macroscopic properties,statistically sampled over specific time intervals in DSMC,along with the turbulent properties provided by the turbulence model,serve as initial conditions for solving the macroscopic synthetic equations.Finally,the simulation particles in DSMC are updated based on the macroscopic properties obtained from the synthetic equations.Numerical simulations demonstrate that the proposed method asymptotically converges to the turbulence model in the continuum regime and to the DSMC method in the rarefied regime,depending on the Knudsen number.This coupling method is then applied to simulate a turbulent opposing jet surrounded by hypersonic rarefied gas flows,revealing significant variations in surface properties due to the interplay of turbulent and rarefied effects.展开更多
The empirical models for wavenumber-frequency spectra of wall pressure are broadly used in the fast prediction of aerodynamic and hydrodynamic noise.However,it needs to fit the parameter using massive data and is only...The empirical models for wavenumber-frequency spectra of wall pressure are broadly used in the fast prediction of aerodynamic and hydrodynamic noise.However,it needs to fit the parameter using massive data and is only used for limited cases.In this letter,we propose Kolmogorov-Arnold networks(KAN)base models for wavenumber-frequency spectra of pressure fluctuations under turbulent boundary layers.The results are compared with DNS results.In turbulent channel flows,it is found that the KAN base model leads to a smooth wavenumber-frequency spectrum with sparse samples.In the turbulent flow over an axisymmetric body of revolution,the KAN base model captures the wavenumber-frequency spectra near the convective peak.展开更多
This work studies the turbulent drag reduction(TDR)effect of a flat plate model using a spanwise slot blowing pulsed plasma actuator(SBP-PA).Wind tunnel experiments are carried out under a Reynolds number of 1.445...This work studies the turbulent drag reduction(TDR)effect of a flat plate model using a spanwise slot blowing pulsed plasma actuator(SBP-PA).Wind tunnel experiments are carried out under a Reynolds number of 1.445×10^(4).Using a hot-wire anemometer and an electrical data acquisition system,the influences of millisecond pulsed plasma actuation with different burst frequencies and duty cycles on the microscale coherent structures near the wall of the turbulent boundary layer(TBL)are studied.The experimental results show that the SBP-PA can effectively reduce the frictional drag of the TBL.When the duty cycle exceeds 30%,the TDR rate is greater than 11%,and the optimal drag reduction rate of 13.69%is obtained at a duty cycle of 50%.Furthermore,optimizing the electrical parameters reveals that increasing the burst frequency significantly reduces the velocity distribution in the logarithmic region of the TBL.When the normalized burst frequency reaches f+=2πf_(p)d/U_(∞)=7.196,the optimal TDR effectiveness is 16.97%,indicating a resonance phenomenon between the pulsed plasma actuation and the microscale coherent structures near the wall.Therefore,reasonably selecting the electrical parameters of the plasma actuator is expected to significantly improve the TDR effect.展开更多
The low-Reynolds-number full developed turbulent flow in channels is simulated using large eddy simulation（LES）method with the preconditioned algorithm and the dynamic subgrid-scale model,with a given disturbance in...The low-Reynolds-number full developed turbulent flow in channels is simulated using large eddy simulation（LES）method with the preconditioned algorithm and the dynamic subgrid-scale model,with a given disturbance in inlet boundary,after a short development section.The inlet Reynolds number based on momentum thickness is 670.The computed results show good agreement with direct numerical simulation（DNS）,which include root mean square fluctuated velocity distribution and average velocity distribution.It is also found that the staggered phenomenon of the coherent structures is caused by sub-harmonic.The results clearly show the formation and evolution of horseshoe vortex in the turbulent boundary layer,including horseshoe vortex structure with a pair of streamwise vortexes and one-side leg of horseshoe vortex.Based on the results,the development of the horseshoe-shaped coherent structures is analyzed in turbulent boundary layer.展开更多
A numerical study analyzed double diffusion caused by convective and radiative heat transfer in a greenhouse with and without internal humidity sources.Two cases were examined:one considering temperature and mass conc...A numerical study analyzed double diffusion caused by convective and radiative heat transfer in a greenhouse with and without internal humidity sources.Two cases were examined:one considering temperature and mass concentration gradients on vertical walls and another incorporating internal humidity sources,enhancing convective and diffusive flows.Four configurations were analyzed by varying the length of the greenhouse,and the Rayleigh number was calculated over a range from 2.29×10^(10) to 6.07×10^(12).Simulations modeled the greenhouse interior six times a day(8:00 a.m.to 7:00 p.m.),accounting for external temperature,humidity,and solar radiation.The Finite Volume Method solved the governing equations using the k-εturbulence model for the turbulent flow regime.Results showed a maximum temperature of 50℃ at 2:50 p.m.and a relative humidity of 84.12%.Adjusting inlet temperature and humidity effectively mitigated external weather effects.Adding humidity sources improved greenhouse performance,increasing humidity concentration by 4.93 to 5.35 times,particularly at 2:50 and 4:20 p.m.Convective and radiative Nusselt and Sherwood numbers were plotted for both cases,revealing higher humidity levels with internal sources,highlighting their importance in optimizing greenhouse microclimates.展开更多
Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds nu...Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds number is Re=6299,and the inlet Hartmann number is Ha=2900,with the magnetic field strength decreasing along the flow direction.The results indicate that the dynamic reversal of the three-dimensional(3D)Lorentz force direction near the inflection point of the magnetic field dominates the flow reconstruction,driving the wall jet acceleration and forming an M-type velocity distribution.Moreover,the high-speed shear layer of the jet triggers Kelvin-Helmholtz instability,resulting in the generation of secondary vortex structures near the parallel layer in the non-uniform magnetic field region.In the cross-section perpendicular to the flow direction,the secondary flow gradually evolves into a four-vortex structure,while the velocity fluctuations and turbulent kinetic energy reach the peak.Based on the characteristics of the vortex rotation direction near the shear layer,the intrinsic mechanism behind the unique bimodal distribution of the root-mean-square of velocity fluctuations in the parallel layers is revealed.Furthermore,by comparing the evolution of turbulence under different magnetic field gradients,it is revealed that the distributions of shear stress,Reynolds stress,and turbulent kinetic energy exhibit significant parameter dependence.The strong 3D magnetohydrodynamic effects at the magnetic field gradientγ=0.6 have an immediate impact on the pressure distribution.The transverse Lorentz force LFz further promotes the fluid to accumulate at the wall,leading to a significant increase in the pressure drop and transverse pressure difference in the flow.展开更多
It is of great significance to improve the accuracy of turbulence models in shock-wave/ boundary layer interaction flow. The relationship between the pressure gradient, as well as the shear layer, and the development ...It is of great significance to improve the accuracy of turbulence models in shock-wave/ boundary layer interaction flow. The relationship between the pressure gradient, as well as the shear layer, and the development of turbulent kinetic energy in impinging shock-wave/turbulent bound- ary layer interaction flow at Mach 2.25 is analyzed based on the data of direct numerical simulation （DNS）. It is found that the turbulent kinetic energy is amplified by strong shear in the separation zone and the adverse pressure gradient near the separation point. The pressure gradient was non-dimensionalised with local density, velocity, and viscosity. Spalart Allmaras （S A） model is modified by introducing the non-dimensional pressure gradient into the production term of the eddy viscosity transportation equation. Simulation results show that the production and dissipation of eddy viscosity are strongly enhanced by the modification of S-A model. Compared with DNS and experimental data, the wall pressure and the wall skin friction coefficient as well as the velocity profile of the modified S-A model are obviously improved. Thus it can be concluded that the mod- ification of S-A model with the pressure gradient can improve the predictive accuracy for simulat- ing the shock-wave/turbulent boundary laver interaction.展开更多
We propose that the core mass function(CMF)can be driven by filament fragmentation.To model a star-forming system of filaments and fibers,we develop a fractal and turbulent tree with a fractal dimension of 2 and a Lar...We propose that the core mass function(CMF)can be driven by filament fragmentation.To model a star-forming system of filaments and fibers,we develop a fractal and turbulent tree with a fractal dimension of 2 and a Larson's law exponent(β)of 0.5.The fragmentation driven by convergent flows along the splines of the fractal tree yields a Kroupa-IMF-like CMF that can be divided into three power-law segments with exponentsα=-0.5,-1.5,and-2,respectively.The turnover masses of the derived CMF are approximately four times those of the Kroupa IMF,corresponding to a star formation efficiency of 0.25.Adoptingβ=1/3,which leads to fractional Brownian motion along the filament,may explain a steeper CMF at the high-mass end,withα=-3.33 close to that of the Salpeter IMF.We suggest that the fibers of the tree are basic building blocks of star formation,with similar properties across different clouds,establishing a common density threshold for star formation and leading to a universal CMF.展开更多
The EHL-2 spherical torus at ENN is the next-generation experimental platform under conceptual design,aiming at realizing proton-boron(p-^(11)B)thermonuclear fusion,which is an attractive pathway towards neutron-free ...The EHL-2 spherical torus at ENN is the next-generation experimental platform under conceptual design,aiming at realizing proton-boron(p-^(11)B)thermonuclear fusion,which is an attractive pathway towards neutron-free fusion.To achieve high-performance steady-state plasma,it is extremely necessary to study the turbulence transport characteristics with high boron content in the plasma core.This study investigates the transport properties in the core internal transport barrier(ITB)region of p-^(11)B plasma utilizing the gyrokinetic code GENE in view of the high ion temperature scenario of EHL-2,specifically focusing on the impact of boron fractions and plasmaβon the microinstabilities and corresponding transport features.Numerical findings indicate that the inclusion of boron species effectively suppresses the trapped electron modes(TEMs)as well as promoting a transition from electromagnetic to electrostatic turbulence with increased boron fraction,which is a result of the suppression of microinstabilities by effective charge and mass.Moreover,it has been identified that the external E×B rotational shear has a notable inhibitory influence on transport,which can reduce the transport level by two to three orders of magnitude,especially at medium boron content.The suppressive effect of E×B on turbulence is weakened once the kinetic ballooning mode(KBM)is excited and the transport shows a rapid increase withβtogether with a reduction in zonal flow amplitude,which is consistent with previous findings.Therefore,it is strongly suggested that exploring advanced strategies for mitigating turbulent transport at highβregimes is necessary for the active control of plasma behavior regarding p-^(11)B plasma-based fusion devices such as EHL-2.展开更多
A numerical analysis of the log-law behavior for the turbulent boundary layer of a wall-bounded flow is performed over a flat plate immersed in three nanofluids(Zn O-water,SiO_(2)-water,TiO_(2)-water).Numerical simula...A numerical analysis of the log-law behavior for the turbulent boundary layer of a wall-bounded flow is performed over a flat plate immersed in three nanofluids(Zn O-water,SiO_(2)-water,TiO_(2)-water).Numerical simulations using CFD code are employed to investigate the boundary layer and the hydrodynamic flow.To validate the current numerical model,measurement points from published works were used,and the compared results were in good compliance.Simulations were carried out for the velocity series of 0.04,0.4 and 4 m/s and nanoparticle concentrations0.1% and 5%.The influence of nanoparticles’ concentration on velocity,temperature profiles,wall shear stress,and turbulent intensity was investigated.The obtained results showed that the viscous sub-layer,the buffer layer,and the loglaw layer along the potential-flow layer could be analyzed based on their curving quality in the regions which have just a single wall distance.It was seen that the viscous sub-layer is the biggest area in comparison with other areas.Alternatively,the section where the temperature changes considerably correspond to the thermal boundary layer’s thickness goes a downward trend when the velocity decreases.The thermal boundary layer gets deep away from the leading edge.However,a rise in the volume fraction of nanoparticles indicated a minor impact on the shear stress developed in the wall.In all cases,the thickness of the boundary layer undergoes a downward trend as the velocity increases,whereas increasing the nanoparticle concentrations would enhance the thickness.More precisely,the log layer is closed with log law,and it is minimal between Y^(+)=50 and Y^(+)=95.The temperature for nanoparticle concentration φ=5%is higher than that for φ=0.1%,in boundary layers,for all studied nanofluids.However,it is established that the behavior is inverted from the value of Y^(+)=1 and the temperature for φ =0.1% is more important than the case of φ =5%.For turbulence intensity peak,this peak exists at Y^(+)=100 for v=4 m/s,Y^(+)=10 for v=0.4 m/s and Y^(+)=8 for v=0.04 m/s.展开更多
The 3-D turbulent flow in the impeller of sewage pump is simulated. Thetime-averaged N-S equations and the kappa-epsilon turbulent model is modified. The calculation iscarried out in body-fitted coordinated grid by ap...The 3-D turbulent flow in the impeller of sewage pump is simulated. Thetime-averaged N-S equations and the kappa-epsilon turbulent model is modified. The calculation iscarried out in body-fitted coordinated grid by applying SIMPLE-C algorithm. The calculated velocity,pressure distributions of the turbulent flow in the sewage pump are obtained for the first time,which will be helpful for the optimal design and performance prediction of sewage pumps on the basisof flow field simulation.展开更多
The flow field inside the combustor of a scramjet is highly complicated and the related turbulent Prandtl and Schmidt numbers have a significant impact on the effective numerical prediction of such dynamics.As in many...The flow field inside the combustor of a scramjet is highly complicated and the related turbulent Prandtl and Schmidt numbers have a significant impact on the effective numerical prediction of such dynamics.As in many cases researchers set these parameters on the basis of purely empirical laws,assessing their impact(via parametric numerical simulations)is a subject of great importance.In the present work,in particular,two test cases with different characteristics are selected for further evaluation of the role played by these non-dimensional numbers:Burrows-Kurkov case and DLR case.The numerical results indicate that these parameters influence ignition location.Moreover,the temperature distribution is more sensitive to them than to H2O mass fraction and velocity distributions.展开更多
Turbulent flow is a basic form of fluid motion widely observed in nature. In hydraulic engineering, especially in the study of sediment movement, turbulence is a key problem. In this paper, based on the stochastic the...Turbulent flow is a basic form of fluid motion widely observed in nature. In hydraulic engineering, especially in the study of sediment movement, turbulence is a key problem. In this paper, based on the stochastic theory of wall turbulence developed by the author and the results by other investigators, fluc-tuation and mean structures and drag coefficient for Newtonian and drag reduction flows in all states (laminar, transitional, turbulent) and in all regions (smooth, transitional, rough) are theoretically discussed in detail. General laws for laminar and turbulent flows obtained by the author are verified by the experimental results obtained by others, and there is good agreement between them.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61971345 and 52107174)。
文摘The primary objective in aircraft transportation is to minimize turbulent drag, thereby conserving energy and reducing emissions. We propose a sector-shaped counter-flow dielectric barrier discharge plasma actuator, which leverages jet synthesis for drag reduction. A drag control experiment was conducted in a low-speed wind tunnel with a controlled flow velocity of 9.6 m/s(Re = 1.445 × 10^(4)). This study investigated the effects of varying pulse frequencies and actuation voltages on the turbulent boundary layer. Using a hot-wire measurement system, we analyzed the pulsating and time-averaged velocity distributions within the boundary layer to evaluate the streamwise turbulent drag reduction. The results show that the local TDR decreases as the pulse frequency increases, reaching a maximum reduction of approximately 20.97% at a pulse frequency of 50 Hz. In addition, as the actuation voltage increases, the friction coefficient decreases, increasing the drag reduction rate. The maximum drag reduction of approximately 33.34% is achieved at an actuation voltage of 10 kV.
基金the Australian Research Council Discovery Project(ARC DP 220100851)scheme and would acknowledge that.
文摘Particle-fluid two-phase flows in rock fractures and fracture networks play a pivotal role in determining the efficiency and effectiveness of hydraulic fracturing operations,a vital component in unconventional oil and gas extraction.Central to this phenomenon is the transport of proppants,tiny solid particles injected into the fractures to prevent them from closing once the injection is stopped.However,effective transport and deposition of proppant is critical in keeping fracture pathways open,especially in lowpermeability reservoirs.This review explores,then quantifies,the important role of fluid inertia and turbulent flows in governing proppant transport.While traditional models predominantly assume and then characterise flow as laminar,this may not accurately capture the complexities inherent in realworld hydraulic fracturing and proppant emplacement.Recent investigations highlight the paramount importance of fluid inertia,especially at the high Reynolds numbers typically associated with fracturing operations.Fluid inertia,often overlooked,introduces crucial forces that influence particle settling velocities,particle-particle interactions,and the eventual deposition of proppants within fractures.With their inherent eddies and transient and chaotic nature,turbulent flows introduce additional complexities to proppant transport,crucially altering proppant settling velocities and dispersion patterns.The following comprehensive survey of experimental,numerical,and analytical studies elucidates controls on the intricate dynamics of proppant transport under fluid inertia and turbulence-towards providing a holistic understanding of the current state-of-the-art,guiding future research directions,and optimising hydraulic fracturing practices.
基金support from the National Key Research and Development Program of China,China(2023YFE0106600)the National Natural Science Foundation of China,China(22421003,22178354,21925805)funding from FFG(Austria)under project“ABATE”(903872).
文摘Liquid-liquid dispersion is often performed in stirred tanks,which are valued for their ease of operation,high droplet generation rate and effective droplet dispersion.Many relevant simulations use the Eulerian-Eulerian method,combining population balance equations with statistical models to forecast droplet breakage.Conversely,the Eulerian-Lagrangian(E-L)method provides precise tracking of individual droplets,which is crucial for simulating dispersion processes.However,E-L simulation faces challenges in integrating droplet breakage effectively.To address this issue,our research introduces a probabilistic approach for droplet breakages.It assumes that a longer time increases the likelihood of breakup;a droplet breaks if the calculated probability exceeds a random value from 0 to 1.Consequently,the simulated breakage frequency becomes independent of the Lagrangian time step.The Sauter mean diameter and droplet size distribution can be accurately predicted by this probabilistic approach.By closely monitoring droplet motion,we reveal the complexity of droplet trajectories and the detailed patterns of circulation in stirred tanks.These insights contribute to a deeper understanding of liquidliquid dispersion dynamics.
基金supported by the National Natural Science Foundation of China(Nos.12232018,12072360)The authors are very grateful to Dr.DONG Siwei for his helpful recommendation on the clustering method.
文摘This study focuses on High-Amplitude Wall Heat Flux events(HAWHFs) occurring during the interaction between a supersonic flat-plate Turbulent Boundary Layer(TBL) at a Mach number of2.25 and an oblique shock wave impinging at 33.2.. A database from a validated direct numerical simulation is analyzed using conditional averaging and a two-dimensional clustering methodology to elucidate the statistical characteristics of both positive and negative HAWHFs within the interaction region. The results reveal that the interaction considerably affects the temporal attributes of the HAWHFs, leading to an extended lifespan for the positive HAWHFs and an increased interval between the occurrences of negative HAWHFs. The structural characteristics of the identified HAWHFs are delineated based on the evolution of population density, aspect ratio, and both absolute and relative distances throughout the interaction. The joint probability density functions of the relative positioning of two adjacent structures indicate that, away from the reattachment point, the positive HAWHFs align in the spanwise direction, displaying similarities with the negative HAWHFs. Moreover, a conditional analysis of flow structures associated with HAWHFs is conducted. This analysis of the conditionally averaged three-dimensional fields reveals that the interaction fosters larger-scale organizational patterns in the downstream region. However, the formation of positive and negative HAWHFs remains largely unaffected by the interaction, with the former predominantly linked to a two-layer temperature structure and the latter primarily associated with a pair of oblique vortices.
基金Supported by the Major Program of the National Natural Science Foundation of China(Grant No.51736007).
文摘In concentric annular pipes,the difference in curvature between the inner and outer wall surfaces creates significant variations in the heat transfer characteristics of the two surfaces.The simplifications of the Dittus-Boelter equation for circular pipes make it unsuitable for the complex flow induced by the geometry and heat transfer coupling effects in annular pipes.This prevents it from accurately predicting the turbulent heat transfer in concentric annular pipes.This paper used realizableκ–εand low Reynolds number models to conduct numerical simulations of turbulent convective heat transfer in concentric annular pipes and circular pipes.The results indicated that the local heat transfer coefficient and Nusselt number of the inner wall surface of the annular pipe were both higher than those of the outer wall surface.The Darcy resistance coefficient decreased upon increasing the Reynolds number and increased with the inner diameter-to-outer diameter ratio.When using the equivalent diameter as the characteristic scale,the turbulent heat transfer correlation obtained from circular pipes produced significant errors when used to approximate the turbulent convective heat transfer in concentric annular pipes.This error was greater for the inner wall surface,especially when the inner and outer diameters were relatively small,as the Nusselt number error on the inner wall surface reached 60.62%.The error of the Nusselt number on the outer wall surface reached 19.51%.
基金Supported by the National Natural Science Foundation of China(No.42276019)the Guangdong Provincial Observation and Research Station for Tropical Ocean Environment in Western Coastal Waters(No.GSTOEW)。
文摘The uncertainty of ocean turbulent mixing parameterization comprises a significant challenge in ocean and climate models. A depth-dependent deep learning ocean turbulent mixing parameterization scheme was proposed with the hydrological and microstructure observations conducted in summer 2012 in the shelf sea east of Hainan Island, in South China Sea(SCS). The deep neural network model is used and incorporates the Richardson number Ri, the normalized depth D, the horizontal velocity speed U, the shear S^(2), the stratification N^(2), and the density ρ as input parameters. Comparing to the scheme without parameter D and region division, the depth-dependent scheme improves the prediction of the turbulent kinetic energy dissipation rate ε. The correlation coefficient(r) between predicted and observed lgε increases from 0.49 to 0.62, and the root mean square error decreases from 0.56 to 0.48. Comparing to the traditional physics-driven parameterization schemes, such as the G89 and MG03, the data-driven approach achieves higher accuracy and generalization. The SHapley Additive Explanations(SHAP) framework analysis reveals the importance descending order of the input parameters as: ρ, D, U, N^(2), S^(2), and Ri in the whole depth, while D is most important in the upper and bottom boundary layers(D≤0.3&D≥0.65) and least important in middle layer(0.3<D<0.65). The research shows applicability of constructing deep learning-based ocean turbulent mixing parameterization schemes using limited observational data and well-established physical processes.
基金supported by the National Key Research and Development Program of China(Grant no.2024YFB3908004).
文摘The North Water Polynya(NOW)is one of the largest and most productive polynyas in the Arctic.Compared to the surrounding sea ice,the combination of high winds and cold air,together with the thin ice or open water surface of the NOW,produces large turbulent heat fluxes(THFs).The accurate estimation of these parameters requires high-resolution atmospheric data,which can be provided by the reanalysis products from different sources.In this study,we calculated the winter latent heat flux(LHF)and sensible heat flux(SHF)over the NOW and its surrounding sea ice area from 2005/2006 to 2015/2016 using high-resolution(15 km)Arctic System Reanalysis version 2(ASRv2)data and low-resolution(30 km)European Centre for Medium-Range Weather Forecasts ERA5 data.Results show that the LHF/SHF over the surrounding sea ice is about 82%/88%lower than over the NOW,as estimated using either dataset.Furthermore,within each area,the difference in the THFs estimated from the two datasets is small.The spatial distribution of the LHF/SHF estimated from both data sources is similar to that of sea ice concentration.The average LHF/SHF in the polynya obtained using ASRv2 data is only 5%/7%higher than that from the values obtained using ERA5 data.This is because the wind speed and air temperature from the ASRv2 data are higher than those of ERA5,and their effects on the THFs can cancel each other out.Furthermore,the estimated THFs do not necessarily improve with the refined resolution of ASRv2.
基金supported by the National Natural Science Foundation of China(Grant No.12450002)。
文摘A multiscale stochastic-deterministic coupling method is proposed to investigate the complex interactions between turbulent and rarefied gas flows within a unified framework.This method intermittently integrates the general synthetic iterative scheme with the shear stress transport turbulence model into the direct simulation Monte Carlo(DSMC)approach,enabling the simulation of gas flows across the free-molecular,transition,slip,and turbulent regimes.First,the macroscopic synthetic equations,derived directly from DSMC,are coupled with the turbulence model to establish a constitutive relation that incorporates not only turbulent and laminar transport coefficients but also higher-order terms accounting for rarefaction effects.Second,the macroscopic properties,statistically sampled over specific time intervals in DSMC,along with the turbulent properties provided by the turbulence model,serve as initial conditions for solving the macroscopic synthetic equations.Finally,the simulation particles in DSMC are updated based on the macroscopic properties obtained from the synthetic equations.Numerical simulations demonstrate that the proposed method asymptotically converges to the turbulence model in the continuum regime and to the DSMC method in the rarefied regime,depending on the Knudsen number.This coupling method is then applied to simulate a turbulent opposing jet surrounded by hypersonic rarefied gas flows,revealing significant variations in surface properties due to the interplay of turbulent and rarefied effects.
基金supported by the National Natural Science Foundation of China Basic Science Center Program for“Multiscale Problems in Nonlinear Mechanics”(Grant No.11988102)the National Natural Science Foundation of China(Grant Nos.92252203,12102439,and 12425207)+1 种基金the Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-087)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB0620102).
文摘The empirical models for wavenumber-frequency spectra of wall pressure are broadly used in the fast prediction of aerodynamic and hydrodynamic noise.However,it needs to fit the parameter using massive data and is only used for limited cases.In this letter,we propose Kolmogorov-Arnold networks(KAN)base models for wavenumber-frequency spectra of pressure fluctuations under turbulent boundary layers.The results are compared with DNS results.In turbulent channel flows,it is found that the KAN base model leads to a smooth wavenumber-frequency spectrum with sparse samples.In the turbulent flow over an axisymmetric body of revolution,the KAN base model captures the wavenumber-frequency spectra near the convective peak.
基金supported by National Natural Science Foundation of China(Nos.61971345 and 12175177)the Foundation for Key Laboratories of National Defense Science and Technology of China(No.614220120030810).
文摘This work studies the turbulent drag reduction(TDR)effect of a flat plate model using a spanwise slot blowing pulsed plasma actuator(SBP-PA).Wind tunnel experiments are carried out under a Reynolds number of 1.445×10^(4).Using a hot-wire anemometer and an electrical data acquisition system,the influences of millisecond pulsed plasma actuation with different burst frequencies and duty cycles on the microscale coherent structures near the wall of the turbulent boundary layer(TBL)are studied.The experimental results show that the SBP-PA can effectively reduce the frictional drag of the TBL.When the duty cycle exceeds 30%,the TDR rate is greater than 11%,and the optimal drag reduction rate of 13.69%is obtained at a duty cycle of 50%.Furthermore,optimizing the electrical parameters reveals that increasing the burst frequency significantly reduces the velocity distribution in the logarithmic region of the TBL.When the normalized burst frequency reaches f+=2πf_(p)d/U_(∞)=7.196,the optimal TDR effectiveness is 16.97%,indicating a resonance phenomenon between the pulsed plasma actuation and the microscale coherent structures near the wall.Therefore,reasonably selecting the electrical parameters of the plasma actuator is expected to significantly improve the TDR effect.
基金Supported by the National Natural Science Foundation of China(10772082)~~
文摘The low-Reynolds-number full developed turbulent flow in channels is simulated using large eddy simulation（LES）method with the preconditioned algorithm and the dynamic subgrid-scale model,with a given disturbance in inlet boundary,after a short development section.The inlet Reynolds number based on momentum thickness is 670.The computed results show good agreement with direct numerical simulation（DNS）,which include root mean square fluctuated velocity distribution and average velocity distribution.It is also found that the staggered phenomenon of the coherent structures is caused by sub-harmonic.The results clearly show the formation and evolution of horseshoe vortex in the turbulent boundary layer,including horseshoe vortex structure with a pair of streamwise vortexes and one-side leg of horseshoe vortex.Based on the results,the development of the horseshoe-shaped coherent structures is analyzed in turbulent boundary layer.
文摘A numerical study analyzed double diffusion caused by convective and radiative heat transfer in a greenhouse with and without internal humidity sources.Two cases were examined:one considering temperature and mass concentration gradients on vertical walls and another incorporating internal humidity sources,enhancing convective and diffusive flows.Four configurations were analyzed by varying the length of the greenhouse,and the Rayleigh number was calculated over a range from 2.29×10^(10) to 6.07×10^(12).Simulations modeled the greenhouse interior six times a day(8:00 a.m.to 7:00 p.m.),accounting for external temperature,humidity,and solar radiation.The Finite Volume Method solved the governing equations using the k-εturbulence model for the turbulent flow regime.Results showed a maximum temperature of 50℃ at 2:50 p.m.and a relative humidity of 84.12%.Adjusting inlet temperature and humidity effectively mitigated external weather effects.Adding humidity sources improved greenhouse performance,increasing humidity concentration by 4.93 to 5.35 times,particularly at 2:50 and 4:20 p.m.Convective and radiative Nusselt and Sherwood numbers were plotted for both cases,revealing higher humidity levels with internal sources,highlighting their importance in optimizing greenhouse microclimates.
基金supported by the Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-087)and the National Key R&D Program of China(Grant No.2022YFA1204100)。
文摘Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds number is Re=6299,and the inlet Hartmann number is Ha=2900,with the magnetic field strength decreasing along the flow direction.The results indicate that the dynamic reversal of the three-dimensional(3D)Lorentz force direction near the inflection point of the magnetic field dominates the flow reconstruction,driving the wall jet acceleration and forming an M-type velocity distribution.Moreover,the high-speed shear layer of the jet triggers Kelvin-Helmholtz instability,resulting in the generation of secondary vortex structures near the parallel layer in the non-uniform magnetic field region.In the cross-section perpendicular to the flow direction,the secondary flow gradually evolves into a four-vortex structure,while the velocity fluctuations and turbulent kinetic energy reach the peak.Based on the characteristics of the vortex rotation direction near the shear layer,the intrinsic mechanism behind the unique bimodal distribution of the root-mean-square of velocity fluctuations in the parallel layers is revealed.Furthermore,by comparing the evolution of turbulence under different magnetic field gradients,it is revealed that the distributions of shear stress,Reynolds stress,and turbulent kinetic energy exhibit significant parameter dependence.The strong 3D magnetohydrodynamic effects at the magnetic field gradientγ=0.6 have an immediate impact on the pressure distribution.The transverse Lorentz force LFz further promotes the fluid to accumulate at the wall,leading to a significant increase in the pressure drop and transverse pressure difference in the flow.
基金supported by the National Natural Science Foundation of China (No.11302012,51376001,51136003)the National Basic Research Program of China (No.2012CB720205)+3 种基金the National Magnetic Confinement Fusion Research Program of China (No.2012GB102006)the Aeronautical Science Foundation of China (No.2012ZB51014)the ‘‘111’’ Project(No.B08009)the Astronautical Technology Innovation Foundation of China
文摘It is of great significance to improve the accuracy of turbulence models in shock-wave/ boundary layer interaction flow. The relationship between the pressure gradient, as well as the shear layer, and the development of turbulent kinetic energy in impinging shock-wave/turbulent bound- ary layer interaction flow at Mach 2.25 is analyzed based on the data of direct numerical simulation （DNS）. It is found that the turbulent kinetic energy is amplified by strong shear in the separation zone and the adverse pressure gradient near the separation point. The pressure gradient was non-dimensionalised with local density, velocity, and viscosity. Spalart Allmaras （S A） model is modified by introducing the non-dimensional pressure gradient into the production term of the eddy viscosity transportation equation. Simulation results show that the production and dissipation of eddy viscosity are strongly enhanced by the modification of S-A model. Compared with DNS and experimental data, the wall pressure and the wall skin friction coefficient as well as the velocity profile of the modified S-A model are obviously improved. Thus it can be concluded that the mod- ification of S-A model with the pressure gradient can improve the predictive accuracy for simulat- ing the shock-wave/turbulent boundary laver interaction.
基金support of the Strategic Priority Research Program of the Chinese Academy of Sciences under grant No.XDB0800303the National Key R&D Program of China under grant No.2022YFA1603100the National Natural Science Foundation of China(NSFC,Grant No.12203086)。
文摘We propose that the core mass function(CMF)can be driven by filament fragmentation.To model a star-forming system of filaments and fibers,we develop a fractal and turbulent tree with a fractal dimension of 2 and a Larson's law exponent(β)of 0.5.The fragmentation driven by convergent flows along the splines of the fractal tree yields a Kroupa-IMF-like CMF that can be divided into three power-law segments with exponentsα=-0.5,-1.5,and-2,respectively.The turnover masses of the derived CMF are approximately four times those of the Kroupa IMF,corresponding to a star formation efficiency of 0.25.Adoptingβ=1/3,which leads to fractional Brownian motion along the filament,may explain a steeper CMF at the high-mass end,withα=-3.33 close to that of the Salpeter IMF.We suggest that the fibers of the tree are basic building blocks of star formation,with similar properties across different clouds,establishing a common density threshold for star formation and leading to a universal CMF.
基金partly supported by SWIP project(No.SWIP-JYHT-12423).
文摘The EHL-2 spherical torus at ENN is the next-generation experimental platform under conceptual design,aiming at realizing proton-boron(p-^(11)B)thermonuclear fusion,which is an attractive pathway towards neutron-free fusion.To achieve high-performance steady-state plasma,it is extremely necessary to study the turbulence transport characteristics with high boron content in the plasma core.This study investigates the transport properties in the core internal transport barrier(ITB)region of p-^(11)B plasma utilizing the gyrokinetic code GENE in view of the high ion temperature scenario of EHL-2,specifically focusing on the impact of boron fractions and plasmaβon the microinstabilities and corresponding transport features.Numerical findings indicate that the inclusion of boron species effectively suppresses the trapped electron modes(TEMs)as well as promoting a transition from electromagnetic to electrostatic turbulence with increased boron fraction,which is a result of the suppression of microinstabilities by effective charge and mass.Moreover,it has been identified that the external E×B rotational shear has a notable inhibitory influence on transport,which can reduce the transport level by two to three orders of magnitude,especially at medium boron content.The suppressive effect of E×B on turbulence is weakened once the kinetic ballooning mode(KBM)is excited and the transport shows a rapid increase withβtogether with a reduction in zonal flow amplitude,which is consistent with previous findings.Therefore,it is strongly suggested that exploring advanced strategies for mitigating turbulent transport at highβregimes is necessary for the active control of plasma behavior regarding p-^(11)B plasma-based fusion devices such as EHL-2.
基金support he received through General Research Project under the grant number (R.G.P.2/138/42)。
文摘A numerical analysis of the log-law behavior for the turbulent boundary layer of a wall-bounded flow is performed over a flat plate immersed in three nanofluids(Zn O-water,SiO_(2)-water,TiO_(2)-water).Numerical simulations using CFD code are employed to investigate the boundary layer and the hydrodynamic flow.To validate the current numerical model,measurement points from published works were used,and the compared results were in good compliance.Simulations were carried out for the velocity series of 0.04,0.4 and 4 m/s and nanoparticle concentrations0.1% and 5%.The influence of nanoparticles’ concentration on velocity,temperature profiles,wall shear stress,and turbulent intensity was investigated.The obtained results showed that the viscous sub-layer,the buffer layer,and the loglaw layer along the potential-flow layer could be analyzed based on their curving quality in the regions which have just a single wall distance.It was seen that the viscous sub-layer is the biggest area in comparison with other areas.Alternatively,the section where the temperature changes considerably correspond to the thermal boundary layer’s thickness goes a downward trend when the velocity decreases.The thermal boundary layer gets deep away from the leading edge.However,a rise in the volume fraction of nanoparticles indicated a minor impact on the shear stress developed in the wall.In all cases,the thickness of the boundary layer undergoes a downward trend as the velocity increases,whereas increasing the nanoparticle concentrations would enhance the thickness.More precisely,the log layer is closed with log law,and it is minimal between Y^(+)=50 and Y^(+)=95.The temperature for nanoparticle concentration φ=5%is higher than that for φ=0.1%,in boundary layers,for all studied nanofluids.However,it is established that the behavior is inverted from the value of Y^(+)=1 and the temperature for φ =0.1% is more important than the case of φ =5%.For turbulence intensity peak,this peak exists at Y^(+)=100 for v=4 m/s,Y^(+)=10 for v=0.4 m/s and Y^(+)=8 for v=0.04 m/s.
文摘The 3-D turbulent flow in the impeller of sewage pump is simulated. Thetime-averaged N-S equations and the kappa-epsilon turbulent model is modified. The calculation iscarried out in body-fitted coordinated grid by applying SIMPLE-C algorithm. The calculated velocity,pressure distributions of the turbulent flow in the sewage pump are obtained for the first time,which will be helpful for the optimal design and performance prediction of sewage pumps on the basisof flow field simulation.
基金supported by grants from the National Natural Science Foundation of China(No.11721202).
文摘The flow field inside the combustor of a scramjet is highly complicated and the related turbulent Prandtl and Schmidt numbers have a significant impact on the effective numerical prediction of such dynamics.As in many cases researchers set these parameters on the basis of purely empirical laws,assessing their impact(via parametric numerical simulations)is a subject of great importance.In the present work,in particular,two test cases with different characteristics are selected for further evaluation of the role played by these non-dimensional numbers:Burrows-Kurkov case and DLR case.The numerical results indicate that these parameters influence ignition location.Moreover,the temperature distribution is more sensitive to them than to H2O mass fraction and velocity distributions.
文摘Turbulent flow is a basic form of fluid motion widely observed in nature. In hydraulic engineering, especially in the study of sediment movement, turbulence is a key problem. In this paper, based on the stochastic theory of wall turbulence developed by the author and the results by other investigators, fluc-tuation and mean structures and drag coefficient for Newtonian and drag reduction flows in all states (laminar, transitional, turbulent) and in all regions (smooth, transitional, rough) are theoretically discussed in detail. General laws for laminar and turbulent flows obtained by the author are verified by the experimental results obtained by others, and there is good agreement between them.
