The process of entrainment-mixing between cumulus clouds and the ambient air is important for the development of cumulus clouds.Accurately obtaining the entrainment rate(λ)is particularly important for its parameteri...The process of entrainment-mixing between cumulus clouds and the ambient air is important for the development of cumulus clouds.Accurately obtaining the entrainment rate(λ)is particularly important for its parameterization within the overall cumulus parameterization scheme.In this study,an improved bulk-plume method is proposed by solving the equations of two conserved variables simultaneously to calculateλof cumulus clouds in a large-eddy simulation.The results demonstrate that the improved bulk-plume method is more reliable than the traditional bulk-plume method,becauseλ,as calculated from the improved method,falls within the range ofλvalues obtained from the traditional method using different conserved variables.The probability density functions ofλfor all data,different times,and different heights can be well-fitted by a log-normal distribution,which supports the assumed stochastic entrainment process in previous studies.Further analysis demonstrate that the relationship betweenλand the vertical velocity is better than other thermodynamic/dynamical properties;thus,the vertical velocity is recommended as the primary influencing factor for the parameterization ofλin the future.The results of this study enhance the theoretical understanding ofλand its influencing factors and shed new light on the development ofλparameterization.展开更多
Compressible flow past a circular cylinder at an inflow Reynolds number of 2×105 is numerically investigated by using a constrained large-eddy simulation(CLES)technique.Numerical simulation with adiabatic wall bo...Compressible flow past a circular cylinder at an inflow Reynolds number of 2×105 is numerically investigated by using a constrained large-eddy simulation(CLES)technique.Numerical simulation with adiabatic wall boundary condition and at a free-stream Mach number of 0.75 is conducted to validate and verify the performance of the present CLES method in predicting separated flows.Some typical and characteristic physical quantities,such as the drag coefficient,the root-mean-square lift fluctuations,the Strouhal number,the pressure and skin friction distributions around the cylinder,etc.are calculated and compared with previously reported experimental data,finer-grid large-eddy simulation(LES)data and those obtained in the present LES and detached-eddy simulation(DES)on coarse grids.It turns out that CLES is superior to DES in predicting such separated flow and that CLES can mimic the intricate shock wave dynamics quite well.Then,the effects of Mach number on the flow patterns and parameters such as the pressure,skin friction and drag coefficients,and the cylinder surface temperature are studied,with Mach number varying from 0.1 to 0.95.Nonmonotonic behaviors of the pressure and skin friction distributions are observed with increasing Mach number and the minimum mean separation angle occurs at a subcritical Mach number of between 0.3 and 0.5.Additionally,the wall temperature effects on the thermodynamic and aerodynamic quantities are explored in a series of simulations using isothermal wall boundary conditions at three different wall temperatures.It is found that the flow separates earlier from the cylinder surface with a longer recirculation length in the wake and a higher pressure coefficient at the rear stagnation point for higher wall temperature.Moreover,the influences of different thermal wall boundary conditions on the flow field are gradually magnified from the front stagnation point to the rear stagnation point.It is inferred that the CLES approach in its current version is a useful and effective tool for simulating wall-bounded compressible turbulent flows with massive separations.展开更多
With the development of computational power and numerical algorithms,computational fluid dynamics(CFD) has become an important strategy for the design of aircraft,which significantly reduces the reliance on wind-tunne...With the development of computational power and numerical algorithms,computational fluid dynamics(CFD) has become an important strategy for the design of aircraft,which significantly reduces the reliance on wind-tunnel and flight tests.In this paper,we conducted a numerical investigation on the flow past a full commercial aircraft at Mach number 0.2 and 14 degrees angle of attack by means of Reynolds-averaged Navier-Stokes(RANS),detached-eddy simulation(DES) and our newly developed constrained large-eddy simulation(CLES).The objective of this paper is to study the capability of these models in simulating turbulent flows.To our knowledge,this is the first large-eddy simulation method for full commercial aircraft simulation.The results show that the CLES can predict the mean statistical quantities well,qualitatively consistent with traditional methods,and can capture more small-scale structures near the surface of the aircraft with massive separations.Our study demonstrates that CLES is a promising alternative for simulating real engineering turbulent flows.展开更多
The gas-droplet two-phase reacting flow in a model combustor with the V-gutter flame holder is studied by an Eulerian-Lagrangian large-eddy simulation (LES) approach. The k-equation subgrid-scale model is used to simu...The gas-droplet two-phase reacting flow in a model combustor with the V-gutter flame holder is studied by an Eulerian-Lagrangian large-eddy simulation (LES) approach. The k-equation subgrid-scale model is used to simulate the subgrid eddy viscosity, and the eddy-break-up (EBU) combustion subgrid-scale model is used to determine the chemical reaction rate. A two-step turbulent combustion subgrid-scale model is employed for calculating carbon monoxide CO concentration, and the NO subgrid-scale pollutant formation model for the evaluation of the rate of NO formation. The heat flux model is applied to the prediction of radiant heat transfer. The gas phase is solved with the SIMPLE algorithm and a hybrid scheme in the staggered grid system. The liquid phase equations are solved in a Lagrangian frame in reference of the particle-source-in-cell (PSIC) algorithm. From simulation results, the exchange of mass, moment and energy between gas and particle fields for the reacting flow in the afterburner with a V-gutter flame holder can be obtained. By the comparison of experimental and simulation results, profile temperature and pollutant of the outlet are quite in agreement with experimental data. Results show that the LES approach for predicting the two-phase instantaneous reacting flow and pollutant emissions in the afterburner is feasible.展开更多
The current research of large eddy simulation （LES） of turbulent flow in pumps mainly concentrates in applying conventional subgrid-scale （SGS） model to simulate turbulent flow, which aims at obtaining the flow fi...The current research of large eddy simulation （LES） of turbulent flow in pumps mainly concentrates in applying conventional subgrid-scale （SGS） model to simulate turbulent flow, which aims at obtaining the flow field in pump. The selection of SGS model is usually not considered seriously, so the accuracy and efficiency of the simulation cannot be ensured. Three SGS models including Smagorinsky-Lilly model, dynamic Smagorinsky model and dynamic mixed model are comparably studied by using the commercial CFD code Fluent combined with its user define function. The simulations are performed for the turbulent flow in a centrifugal pump impeller. The simulation results indicate that the mean flows predicted by the three SGS models agree well with the experimental data obtained from the test that detailed measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller performed using particle image velocimetry （PIV） and laser Doppler velocimetry （LDV）. The comparable results show that dynamic mixed model gives the most accurate results for mean flow in the centrifugal pump impeller. The SGS stress of dynamic mixed model is decompose into the scale similar part and the eddy viscous part. The scale similar part of SGS stress plays a significant role in high curvature regions, such as the leading edge and training edge of pump blade. It is also found that the dynamic mixed model is more adaptive to compute turbulence in the pump impeller. The research results presented is useful to improve the computational accuracy and efficiency of LES for centrifugal pumps, and provide important reference for carrying out simulation in similar fluid machineries.展开更多
A novel method is proposed to combine the wall-modeled large-eddy simulation(LES) with the diffuse-interface direct-forcing immersed boundary(IB) method.The new developments in this method include:(i) the momentum equ...A novel method is proposed to combine the wall-modeled large-eddy simulation(LES) with the diffuse-interface direct-forcing immersed boundary(IB) method.The new developments in this method include:(i) the momentum equation is integrated along the wall-normal direction to link the tangential component of the effective body force for the IB method to the wall shear stress predicted by the wall model;(ii) a set of Lagrangian points near the wall are introduced to compute the normal component of the effective body force for the IB method by reconstructing the normal component of the velocity. This novel method will be a classical direct-forcing IB method if the grid is fine enough to resolve the flow near the wall. The method is used to simulate the flows around the DARPA SUBOFF model. The results obtained are well comparable to the measured experimental data and wall-resolved LES results.展开更多
Eddy-damping quasinormal Markovian （EDQNM） theory is employed to calculate the resolved-scale spectrum and transfer spectrum, based on which we investigate the resolved-scale scaling law. Results show that the scali...Eddy-damping quasinormal Markovian （EDQNM） theory is employed to calculate the resolved-scale spectrum and transfer spectrum, based on which we investigate the resolved-scale scaling law. Results show that the scaling law of the resolved-scale turbulence, which is affected by several factors, is far from that of the full-scale turbulence and should be corrected. These results are then applied to an existing subgrid model to improve its performance. A series of simulations are performed to verify the necessity of a fixed scaling law in the subgrid modeling.展开更多
In this work we extend the method of the constrained large-eddy simulation(CLES)to simulate the tur-bulent flow over inhomogeneous rough walls.In the original concept of CLES,the subgrid-scale(SGS)stress is constraine...In this work we extend the method of the constrained large-eddy simulation(CLES)to simulate the tur-bulent flow over inhomogeneous rough walls.In the original concept of CLES,the subgrid-scale(SGS)stress is constrained so that the mean part and the fluctuation part of the SGS stress can be modelled separately to improve the accuracy of the simulation result.Here in the simulation of the rough-wall flows,we propose to interpret the extra stress terms in the CLES formulation as the roughness-induced stress so that the roughness inhomogeneity can be incorporated by modifying the formulation of the constrained SGS stress.This is examined with the simulations of the channel flow with the spanwise alternating high/low roughness strips.Then the CLES method is employed to investigate the temporal response of the turbulence to the change of the wall condition from rough to smooth.We demonstrate that the temporal development of the internal boundary layer is just similar to that in a spatial rough-to-smooth transition process,and the spanwise roughness inhomogeneity has little impact on the transition process.展开更多
In recent years, sinmlated annealing algo-rithms have been extensively developed and uti-lized to solve nmlti-objective optimization problems. In order to obtain better optimization perfonmnce, this paper proposes a N...In recent years, sinmlated annealing algo-rithms have been extensively developed and uti-lized to solve nmlti-objective optimization problems. In order to obtain better optimization perfonmnce, this paper proposes a Novel Adaptive Simulated Annealing （NASA） algorithm for constrained multi-objective optimization based on Archived Multi-objective Simulated Annealing （AMOSA）. For han-dling multi-objective, NASA makes improverrents in three aspects： sub-iteration search, sub-archive and adaptive search, which effectively strengthen the stability and efficiency of the algorithnm For handling constraints, NASA introduces corresponding solution acceptance criterion. Furtherrrore, NASA has also been applied to optimize TD-LTE network perform-ance by adjusting antenna paranleters; it can achieve better extension and convergence than AMOSA, NS-GAII and MOPSO. Analytical studies and simulations indicate that the proposed NASA algorithm can play an important role in improving multi-objective optimi-zation performance.展开更多
The flows past a number 3900 are simulated circular cylinder at Reynolds using large-eddy simulation （LES） and the far-field sound is calculated from the LES results. A low dissipation energy-conserving finite volum...The flows past a number 3900 are simulated circular cylinder at Reynolds using large-eddy simulation （LES） and the far-field sound is calculated from the LES results. A low dissipation energy-conserving finite volume scheme is used to discretize the incompressible Navier- Stokes equations. The dynamic global coefficient version of the Vreman＇s subgrid scale （SGS） model is used to com- pute the sub-grid stresses. Curie＇s integral of Lighthill＇s acoustic analogy is used to extract the sound radiated from the cylinder. The profiles of mean velocity and turbulent fluctua- tions obtained are consistent with the previous experimental and computational results. The sound radiation at far field exhibits the characteristic of a dipole and directivity. The sound spectra display the -5/3 power law. It is shown that Vreman＇s SGS model in company with dynamic procedure is suitable for LES of turbulence generated noise.展开更多
The entrainment flux ratio Ae and the inversion layer （IL） thickness are two key parameters in a mixed layer model. Ae is defined as the ratio of the entrainment heat flux at the mixed layer top to the surface heat ...The entrainment flux ratio Ae and the inversion layer （IL） thickness are two key parameters in a mixed layer model. Ae is defined as the ratio of the entrainment heat flux at the mixed layer top to the surface heat flux. The IL is the layer between the mixed layer and the free atmosphere. In this study, a parameterization of Ae is derived from the TKE budget in the first- order model for a well-developed CBL under the condition of linearly sheared geostrophic velocity with a zero value at the surface. It is also appropriate for a CBL under the condition of geostrophic velocity remaining constant with height. LESs are conducted under the above two conditions to determine the coefficients in the parameterization scheme. Results suggest that about 43% of the shear-produced TKE in the IL is available for entrainment, while the shear-produced TKE in the mixed layer and surface layer have little effect on entrainment. Based on this scheme, a new scale of convective turbulence velocity is proposed and applied to parameterize the IL thickness, The LES outputs for the CBLs under the condition of linearly sheared geostrophic velocity with a non-zero surface value are used to verify the performance of the parameterization scheme. It is found that the parameterized Ae and IL thickness agree well with the LES outputs.展开更多
The so-called T-shaped reducing tees are typically used to divide,change and control(to a certain extent)the flow direction in pipe networks.In this study,the Ffowcs Williams–Hawkings(FW-H)equation and the Large Eddy...The so-called T-shaped reducing tees are typically used to divide,change and control(to a certain extent)the flow direction in pipe networks.In this study,the Ffowcs Williams–Hawkings(FW-H)equation and the Large Eddy Simulation(LES)methods are used to simulate the flow-induced noise related to T-shaped reducing tees under different inlet flow velocities and for different pipe diameter ratios.The results show that the maximum flow velocity,average flow velocity,and vorticity in the branch pipe increase gradually as the related diameter decreases.Strong vorticity and secondary flows are also observed in the branch pipe,and the associated violent pressure fluctuations are found to be the main sources of flow-induced noise.In particular,as the pipe diameter ratio decreases from 1 to 0.45,the Total Sound Pressure Level(TSPL)increases by 6.8,6.26,and 7.43 dB for values of the inlet flow velocity of 1,2,and 3 m/s,respectively.The distribution characteristics of the flow-induced noise in the frequency domain follow similar trends for different pipe diameter ratios.展开更多
The temperature fluctuation caused by thermal striping phenomena of hot and cold fluids mixing results in cyclical thermal stress fatigue failure of the pipe wall. Mean temperature difference between hot and cold flui...The temperature fluctuation caused by thermal striping phenomena of hot and cold fluids mixing results in cyclical thermal stress fatigue failure of the pipe wall. Mean temperature difference between hot and cold fluids was often used as thermal load in previous analysis of thermal fatigue failure, thereby the influences of the amplitude and frequency of temperature fluctuation on thermal fatigue failure were neglected. Based on the mechanism of flow and heat transfer which induces thermal fatigue, the turbulent mixing of hot and cold water in a tee junction is simulated with FLUENT platform by using the Large-eddy simulation（LES） turbulent flow model with the sub-grid scale（SGS） model of Smagorinsky-Lilly（SL） to capture the amplitude and frequency of temperature fluctuation. In a simulation case, hot water with temperature of 343.48 K and velocity of 0.15 m/s enters the horizontal main duct with the side length of 100 mm, while cold water with temperature of 296.78 K and velocity of 0.3 m/s enters the vertical branch duct with the side length of 50 mm. The numerical results show that the mean and fluctuating temperatures are in good agreement with the previous experimental data, which describes numerical simulation with high reliability and accuracy; the power spectrum density（PSD） on top wall is higher than that on bottom wall（as the frequency less than 1 Hz）, while the PSD on bottom wall is relatively higher than that on top wall （as the frequency of 1-10Hz）. The temperature fluctuations in full mixing region of the tee junction can be accurately captured by LES and can provide the theoretical basis for the thermal stress and thermal fatigue analyses.展开更多
The Large-eddy simulation (LES) with two-way coupling is used to study bubble-liquid two-phase confined multiple jets discharged into a 2D channel.The LES results reveal the large-eddy vortex structures of both liquid...The Large-eddy simulation (LES) with two-way coupling is used to study bubble-liquid two-phase confined multiple jets discharged into a 2D channel.The LES results reveal the large-eddy vortex structures of both liquid flow and bubble motion,the shear-generated and bubble-induced liquid turbulence,and indicate much stronger bubble fluctuation than that of the liquid,the enhancement of liquid turbulence by bubbles.Both shear and bubble-liquid interaction are important for the liquid turbulence generation in the case studied.展开更多
Mixing processes of hot and cold fluids in a tee with and without sin- tered copper spheres are simulated by FLUENT using the large-eddy simulation （LES） turbulent flow model and the sub-grid scale （SGS） Smagorins...Mixing processes of hot and cold fluids in a tee with and without sin- tered copper spheres are simulated by FLUENT using the large-eddy simulation （LES） turbulent flow model and the sub-grid scale （SGS） Smagorinsky-Lilly （SL） model with buoyancy. Comparisons of numerical results of the two cases with and without sintered copper spheres show that the porous medium significantly reduces velocity and temper- ature fluctuations because the porous medium can effectively restrict the fluid flow and enhance heat transfer. The porous medium obviously increases the pressure drop in the main duct. The porous medium reduces the power spectrum density （PSD） of tempera- ture fluctuations in the frequency range from 1 Hz to 10 Hz.展开更多
In a large wind farm,the wakes of upstream and downstream wind turbines can interfere with each other,affecting the overall power output of the wind farm.To further improve the numerical accuracy of the turbine wake d...In a large wind farm,the wakes of upstream and downstream wind turbines can interfere with each other,affecting the overall power output of the wind farm.To further improve the numerical accuracy of the turbine wake dynamics under atmosphere turbulence,this work proposes some improvements to the actuator line-large-eddy simulation(AL-LES)method.Based on the dynamic k-equation large-eddy simulation(LES),this method uses a precursor method to generate atmospheric inflow turbulence,models the tower and nacelle wakes,and improves the body force projection method based on an anisotropic Gaussian distribution function.For these three improvements,three wind tunnel experiments are used to validate the numerical accuracy of this method.The results show that the numerical results calculated in the far-wake region can reflect the characteristics of typical onshore and offshore wind conditions compared with the experimental results.After modeling the tower and nacelle wakes,the wake velocity distribution is consistent with the experimental result.The radial migration velocity of the tip vortex calculated by the improved blade body force distribution model is 0.32 m/s,which is about 6%different from the experimental value and improves the prediction accuracy of the tip vortex radial movement.The method proposed in this paper is very helpful for wind turbine wake dynamic analysis and wind farm power prediction.展开更多
Spray combustion is widely used in power, transportation, chemical and metallurgical, iron and steel making, aeronautical and astronautical engineering. In recent years, large-eddy simulation (LES) becomes more and mo...Spray combustion is widely used in power, transportation, chemical and metallurgical, iron and steel making, aeronautical and astronautical engineering. In recent years, large-eddy simulation (LES) becomes more and more attractive, because it can give the instantaneous flow and flame structures, and may give more accurate statistical results than the Reynolds averaged Navier-Stokes (RANS) modeling. In this paper, the present status of the studies on LES of spray combustion is reviewed, and the future research needs are discussed.展开更多
A hybrid method is presented to numerically investigate the wind turbine aerodynamic characteristics.The wind turbine blade is replaced by an actuator line model.Turbulence is treated using a dynamic one-equation subg...A hybrid method is presented to numerically investigate the wind turbine aerodynamic characteristics.The wind turbine blade is replaced by an actuator line model.Turbulence is treated using a dynamic one-equation subgrid-scale model in large eddy simulation.Detailed information on the basic characteristics of the wind turbine wake is obtained and discussed.The rotor aerodynamic performance agrees well with the measurements.The actuator line method large-eddy simulation(ALM-LES)technique demonstrates its high potential in providing accurate load prediction and high resolution of turbulent fluctuations in the wind turbine wakes and the interactions within a feasible cost.展开更多
Oceanic turbulence plays an important role in coastal flow. However, as the effect of an uneven lower boundary on the adjacent turbulence is still not well understood, we explore the mechanics of nearshore turbulence ...Oceanic turbulence plays an important role in coastal flow. However, as the effect of an uneven lower boundary on the adjacent turbulence is still not well understood, we explore the mechanics of nearshore turbulence with a turbulence-resolving numerical model known as a large-eddy-simulation model for an idealized scenario in a coastal region for which the lower boundary is a solid sinusoidal wave. The numerical simulation demonstrates how the mechanical energy of the current is transferred into local turbulence mixing, and shows the changes in turbulent intensity over the continuous phase change of the lower topography. The strongest turbulent kinetic energy is concentrated above the trough of the wavy surface. The turbulence mixing is mainly generated by the shear forces; the magnitude of shear production has a local maximum over the crest of the seabed topography, and there is an asymmetry in the shear production between the leeward and windward slopes. The numerical results are consistent with results from laboratory experiments. Our analysis provides an important insight into the mechanism of turbulent kinetic energy production and development.展开更多
Large-eddy simulation of spray combustion is under its rapid development.Different combustion models were used by different investigators.However,these models are less validated by detailed experimental data.In this p...Large-eddy simulation of spray combustion is under its rapid development.Different combustion models were used by different investigators.However,these models are less validated by detailed experimental data.In this paper,large-eddy simulation(LES)of ethanol spray-air combustion was made using an Eulerian-Lagrangian approach,a subgrid-scale kinetic energy stress model,and a filtered finite-rate combustion model,neglecting the sub-grid scale reaction rate.The simulation results are compared with experimental dada in the literature and validated in detail.The LES obtained statistically averaged gas temperature is in much better agreement with the experimental results than Reynolds averaged(RANS)modeling using the most complex probability density function(PDF)equation combustion model.The instantaneous LES results show the coherent structures of the shear region near the high-temperature flame zone and the fuel vapor concentration map,indicating that the droplets are concentrated in this shear region.The instantaneous temperature,oxygen and carbon dioxide concentration maps show the close interaction between the coherent structures and the combustion reaction.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.42175099,42027804,42075073)the Innovative Project of Postgraduates in Jiangsu Province in 2023(Grant No.KYCX23_1319)+3 种基金supported by the National Natural Science Foundation of China(Grant No.42205080)the Natural Science Foundation of Sichuan(Grant No.2023YFS0442)the Research Fund of Civil Aviation Flight University of China(Grant No.J2022-037)supported by the National Key Scientific and Technological Infrastructure project“Earth System Science Numerical Simulator Facility”(Earth Lab)。
文摘The process of entrainment-mixing between cumulus clouds and the ambient air is important for the development of cumulus clouds.Accurately obtaining the entrainment rate(λ)is particularly important for its parameterization within the overall cumulus parameterization scheme.In this study,an improved bulk-plume method is proposed by solving the equations of two conserved variables simultaneously to calculateλof cumulus clouds in a large-eddy simulation.The results demonstrate that the improved bulk-plume method is more reliable than the traditional bulk-plume method,becauseλ,as calculated from the improved method,falls within the range ofλvalues obtained from the traditional method using different conserved variables.The probability density functions ofλfor all data,different times,and different heights can be well-fitted by a log-normal distribution,which supports the assumed stochastic entrainment process in previous studies.Further analysis demonstrate that the relationship betweenλand the vertical velocity is better than other thermodynamic/dynamical properties;thus,the vertical velocity is recommended as the primary influencing factor for the parameterization ofλin the future.The results of this study enhance the theoretical understanding ofλand its influencing factors and shed new light on the development ofλparameterization.
基金support from National Natural Science Foundation of China(Grants No.91130001 and No.11221061)supported by the National Basic Research Program of China(Grant No.2009CB724101)support from National Science Foundation for Postdoctoral Scientists of China(Grant No.2012M520109).
文摘Compressible flow past a circular cylinder at an inflow Reynolds number of 2×105 is numerically investigated by using a constrained large-eddy simulation(CLES)technique.Numerical simulation with adiabatic wall boundary condition and at a free-stream Mach number of 0.75 is conducted to validate and verify the performance of the present CLES method in predicting separated flows.Some typical and characteristic physical quantities,such as the drag coefficient,the root-mean-square lift fluctuations,the Strouhal number,the pressure and skin friction distributions around the cylinder,etc.are calculated and compared with previously reported experimental data,finer-grid large-eddy simulation(LES)data and those obtained in the present LES and detached-eddy simulation(DES)on coarse grids.It turns out that CLES is superior to DES in predicting such separated flow and that CLES can mimic the intricate shock wave dynamics quite well.Then,the effects of Mach number on the flow patterns and parameters such as the pressure,skin friction and drag coefficients,and the cylinder surface temperature are studied,with Mach number varying from 0.1 to 0.95.Nonmonotonic behaviors of the pressure and skin friction distributions are observed with increasing Mach number and the minimum mean separation angle occurs at a subcritical Mach number of between 0.3 and 0.5.Additionally,the wall temperature effects on the thermodynamic and aerodynamic quantities are explored in a series of simulations using isothermal wall boundary conditions at three different wall temperatures.It is found that the flow separates earlier from the cylinder surface with a longer recirculation length in the wake and a higher pressure coefficient at the rear stagnation point for higher wall temperature.Moreover,the influences of different thermal wall boundary conditions on the flow field are gradually magnified from the front stagnation point to the rear stagnation point.It is inferred that the CLES approach in its current version is a useful and effective tool for simulating wall-bounded compressible turbulent flows with massive separations.
基金supported by the National Natural Science Foundation of China(Grant Nos.10921202 and 91130001)the National Basic Research Program of China(Grant No. 2009CB724101)
文摘With the development of computational power and numerical algorithms,computational fluid dynamics(CFD) has become an important strategy for the design of aircraft,which significantly reduces the reliance on wind-tunnel and flight tests.In this paper,we conducted a numerical investigation on the flow past a full commercial aircraft at Mach number 0.2 and 14 degrees angle of attack by means of Reynolds-averaged Navier-Stokes(RANS),detached-eddy simulation(DES) and our newly developed constrained large-eddy simulation(CLES).The objective of this paper is to study the capability of these models in simulating turbulent flows.To our knowledge,this is the first large-eddy simulation method for full commercial aircraft simulation.The results show that the CLES can predict the mean statistical quantities well,qualitatively consistent with traditional methods,and can capture more small-scale structures near the surface of the aircraft with massive separations.Our study demonstrates that CLES is a promising alternative for simulating real engineering turbulent flows.
文摘The gas-droplet two-phase reacting flow in a model combustor with the V-gutter flame holder is studied by an Eulerian-Lagrangian large-eddy simulation (LES) approach. The k-equation subgrid-scale model is used to simulate the subgrid eddy viscosity, and the eddy-break-up (EBU) combustion subgrid-scale model is used to determine the chemical reaction rate. A two-step turbulent combustion subgrid-scale model is employed for calculating carbon monoxide CO concentration, and the NO subgrid-scale pollutant formation model for the evaluation of the rate of NO formation. The heat flux model is applied to the prediction of radiant heat transfer. The gas phase is solved with the SIMPLE algorithm and a hybrid scheme in the staggered grid system. The liquid phase equations are solved in a Lagrangian frame in reference of the particle-source-in-cell (PSIC) algorithm. From simulation results, the exchange of mass, moment and energy between gas and particle fields for the reacting flow in the afterburner with a V-gutter flame holder can be obtained. By the comparison of experimental and simulation results, profile temperature and pollutant of the outlet are quite in agreement with experimental data. Results show that the LES approach for predicting the two-phase instantaneous reacting flow and pollutant emissions in the afterburner is feasible.
基金supported by National Natural Science Foundation of China (Grant Nos. 51139007, 51079151, 51079152)Research Fundfor the Doctoral Program of Higher Education of China (Grant No. 0100008110012)
文摘The current research of large eddy simulation （LES） of turbulent flow in pumps mainly concentrates in applying conventional subgrid-scale （SGS） model to simulate turbulent flow, which aims at obtaining the flow field in pump. The selection of SGS model is usually not considered seriously, so the accuracy and efficiency of the simulation cannot be ensured. Three SGS models including Smagorinsky-Lilly model, dynamic Smagorinsky model and dynamic mixed model are comparably studied by using the commercial CFD code Fluent combined with its user define function. The simulations are performed for the turbulent flow in a centrifugal pump impeller. The simulation results indicate that the mean flows predicted by the three SGS models agree well with the experimental data obtained from the test that detailed measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller performed using particle image velocimetry （PIV） and laser Doppler velocimetry （LDV）. The comparable results show that dynamic mixed model gives the most accurate results for mean flow in the centrifugal pump impeller. The SGS stress of dynamic mixed model is decompose into the scale similar part and the eddy viscous part. The scale similar part of SGS stress plays a significant role in high curvature regions, such as the leading edge and training edge of pump blade. It is also found that the dynamic mixed model is more adaptive to compute turbulence in the pump impeller. The research results presented is useful to improve the computational accuracy and efficiency of LES for centrifugal pumps, and provide important reference for carrying out simulation in similar fluid machineries.
基金Project supported by the National Natural Science Foundation of China(Nos.91752118,11672305,11232011,and 11572331)the Strategic Priority Research Program(No.XDB22040104)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(No.QYZDJ-SSWSYS002)
文摘A novel method is proposed to combine the wall-modeled large-eddy simulation(LES) with the diffuse-interface direct-forcing immersed boundary(IB) method.The new developments in this method include:(i) the momentum equation is integrated along the wall-normal direction to link the tangential component of the effective body force for the IB method to the wall shear stress predicted by the wall model;(ii) a set of Lagrangian points near the wall are introduced to compute the normal component of the effective body force for the IB method by reconstructing the normal component of the velocity. This novel method will be a classical direct-forcing IB method if the grid is fine enough to resolve the flow near the wall. The method is used to simulate the flows around the DARPA SUBOFF model. The results obtained are well comparable to the measured experimental data and wall-resolved LES results.
基金supported by the National Natural Science Foundation of China(11202013 and 51136003)the National Basic Research Program of China(2012CB720200)the Opening fundof State Key Laboratory of Nonlinear Mechanics
文摘Eddy-damping quasinormal Markovian （EDQNM） theory is employed to calculate the resolved-scale spectrum and transfer spectrum, based on which we investigate the resolved-scale scaling law. Results show that the scaling law of the resolved-scale turbulence, which is affected by several factors, is far from that of the full-scale turbulence and should be corrected. These results are then applied to an existing subgrid model to improve its performance. A series of simulations are performed to verify the necessity of a fixed scaling law in the subgrid modeling.
基金supported by the National Natural Science Foundation of China (Grants 11988102, 91752201, and 11822208)the Department of Science and Technology of Guangdong Province (Grant 2019B21203001)+3 种基金Key Special Project for Introduced Tal ents Team of Southern Marine Science and Engineering Guang dong Laboratory (Guangzhou) (Grant GML2019ZD0103)Shenzhen Science & Technology Program (Grant KQTD2018 0411143441009)supported by Center for Computational Science and Engineering of Southern University of Science and Technologythe support from Centers for Mechanical Engineering Research and Education at MIT and SUSTech
文摘In this work we extend the method of the constrained large-eddy simulation(CLES)to simulate the tur-bulent flow over inhomogeneous rough walls.In the original concept of CLES,the subgrid-scale(SGS)stress is constrained so that the mean part and the fluctuation part of the SGS stress can be modelled separately to improve the accuracy of the simulation result.Here in the simulation of the rough-wall flows,we propose to interpret the extra stress terms in the CLES formulation as the roughness-induced stress so that the roughness inhomogeneity can be incorporated by modifying the formulation of the constrained SGS stress.This is examined with the simulations of the channel flow with the spanwise alternating high/low roughness strips.Then the CLES method is employed to investigate the temporal response of the turbulence to the change of the wall condition from rough to smooth.We demonstrate that the temporal development of the internal boundary layer is just similar to that in a spatial rough-to-smooth transition process,and the spanwise roughness inhomogeneity has little impact on the transition process.
基金supported by the Major National Science & Technology Specific Project of China under Grants No.2010ZX03002-007-02,No.2009ZX03002-002,No.2010ZX03002-002-03
文摘In recent years, sinmlated annealing algo-rithms have been extensively developed and uti-lized to solve nmlti-objective optimization problems. In order to obtain better optimization perfonmnce, this paper proposes a Novel Adaptive Simulated Annealing （NASA） algorithm for constrained multi-objective optimization based on Archived Multi-objective Simulated Annealing （AMOSA）. For han-dling multi-objective, NASA makes improverrents in three aspects： sub-iteration search, sub-archive and adaptive search, which effectively strengthen the stability and efficiency of the algorithnm For handling constraints, NASA introduces corresponding solution acceptance criterion. Furtherrrore, NASA has also been applied to optimize TD-LTE network perform-ance by adjusting antenna paranleters; it can achieve better extension and convergence than AMOSA, NS-GAII and MOPSO. Analytical studies and simulations indicate that the proposed NASA algorithm can play an important role in improving multi-objective optimi-zation performance.
基金supported by the National Natural Science Foundation of China(Grant 11232011)
文摘The flows past a number 3900 are simulated circular cylinder at Reynolds using large-eddy simulation （LES） and the far-field sound is calculated from the LES results. A low dissipation energy-conserving finite volume scheme is used to discretize the incompressible Navier- Stokes equations. The dynamic global coefficient version of the Vreman＇s subgrid scale （SGS） model is used to com- pute the sub-grid stresses. Curie＇s integral of Lighthill＇s acoustic analogy is used to extract the sound radiated from the cylinder. The profiles of mean velocity and turbulent fluctua- tions obtained are consistent with the previous experimental and computational results. The sound radiation at far field exhibits the characteristic of a dipole and directivity. The sound spectra display the -5/3 power law. It is shown that Vreman＇s SGS model in company with dynamic procedure is suitable for LES of turbulence generated noise.
基金sponsored by the National Natural Science Foundation of China(Grant No.40975004)the State Key Basic Program(973)Program(Grant No.2013CB430100)
文摘The entrainment flux ratio Ae and the inversion layer （IL） thickness are two key parameters in a mixed layer model. Ae is defined as the ratio of the entrainment heat flux at the mixed layer top to the surface heat flux. The IL is the layer between the mixed layer and the free atmosphere. In this study, a parameterization of Ae is derived from the TKE budget in the first- order model for a well-developed CBL under the condition of linearly sheared geostrophic velocity with a zero value at the surface. It is also appropriate for a CBL under the condition of geostrophic velocity remaining constant with height. LESs are conducted under the above two conditions to determine the coefficients in the parameterization scheme. Results suggest that about 43% of the shear-produced TKE in the IL is available for entrainment, while the shear-produced TKE in the mixed layer and surface layer have little effect on entrainment. Based on this scheme, a new scale of convective turbulence velocity is proposed and applied to parameterize the IL thickness, The LES outputs for the CBLs under the condition of linearly sheared geostrophic velocity with a non-zero surface value are used to verify the performance of the parameterization scheme. It is found that the parameterized Ae and IL thickness agree well with the LES outputs.
基金supported by the Shandong Engineering Laboratory for High-Efficiency Energy Conservation and Energy Storage Technology&Equipment.
文摘The so-called T-shaped reducing tees are typically used to divide,change and control(to a certain extent)the flow direction in pipe networks.In this study,the Ffowcs Williams–Hawkings(FW-H)equation and the Large Eddy Simulation(LES)methods are used to simulate the flow-induced noise related to T-shaped reducing tees under different inlet flow velocities and for different pipe diameter ratios.The results show that the maximum flow velocity,average flow velocity,and vorticity in the branch pipe increase gradually as the related diameter decreases.Strong vorticity and secondary flows are also observed in the branch pipe,and the associated violent pressure fluctuations are found to be the main sources of flow-induced noise.In particular,as the pipe diameter ratio decreases from 1 to 0.45,the Total Sound Pressure Level(TSPL)increases by 6.8,6.26,and 7.43 dB for values of the inlet flow velocity of 1,2,and 3 m/s,respectively.The distribution characteristics of the flow-induced noise in the frequency domain follow similar trends for different pipe diameter ratios.
基金supported by National Natural Science Foundation of China(Grant No. 50906002)National Basic Research Program of China(973 Program, Grant No. 2011CB706900)Beijing Novel Program of China(Grant No. 2008B16)
文摘The temperature fluctuation caused by thermal striping phenomena of hot and cold fluids mixing results in cyclical thermal stress fatigue failure of the pipe wall. Mean temperature difference between hot and cold fluids was often used as thermal load in previous analysis of thermal fatigue failure, thereby the influences of the amplitude and frequency of temperature fluctuation on thermal fatigue failure were neglected. Based on the mechanism of flow and heat transfer which induces thermal fatigue, the turbulent mixing of hot and cold water in a tee junction is simulated with FLUENT platform by using the Large-eddy simulation（LES） turbulent flow model with the sub-grid scale（SGS） model of Smagorinsky-Lilly（SL） to capture the amplitude and frequency of temperature fluctuation. In a simulation case, hot water with temperature of 343.48 K and velocity of 0.15 m/s enters the horizontal main duct with the side length of 100 mm, while cold water with temperature of 296.78 K and velocity of 0.3 m/s enters the vertical branch duct with the side length of 50 mm. The numerical results show that the mean and fluctuating temperatures are in good agreement with the previous experimental data, which describes numerical simulation with high reliability and accuracy; the power spectrum density（PSD） on top wall is higher than that on bottom wall（as the frequency less than 1 Hz）, while the PSD on bottom wall is relatively higher than that on top wall （as the frequency of 1-10Hz）. The temperature fluctuations in full mixing region of the tee junction can be accurately captured by LES and can provide the theoretical basis for the thermal stress and thermal fatigue analyses.
基金Supported by the National Natural Science Foundation of China (No. 19872039).
文摘The Large-eddy simulation (LES) with two-way coupling is used to study bubble-liquid two-phase confined multiple jets discharged into a 2D channel.The LES results reveal the large-eddy vortex structures of both liquid flow and bubble motion,the shear-generated and bubble-induced liquid turbulence,and indicate much stronger bubble fluctuation than that of the liquid,the enhancement of liquid turbulence by bubbles.Both shear and bubble-liquid interaction are important for the liquid turbulence generation in the case studied.
基金supported by the National Natural Science Foundation of China (No. 50906002)the National Basic Research Program of China (No. 2011CB706900)+1 种基金the Research Fund for the Doctoral Program of Higher Education of China (No. 20090010110006)the Beijing Novel Program of China (No. 2008B16)
文摘Mixing processes of hot and cold fluids in a tee with and without sin- tered copper spheres are simulated by FLUENT using the large-eddy simulation （LES） turbulent flow model and the sub-grid scale （SGS） Smagorinsky-Lilly （SL） model with buoyancy. Comparisons of numerical results of the two cases with and without sintered copper spheres show that the porous medium significantly reduces velocity and temper- ature fluctuations because the porous medium can effectively restrict the fluid flow and enhance heat transfer. The porous medium obviously increases the pressure drop in the main duct. The porous medium reduces the power spectrum density （PSD） of tempera- ture fluctuations in the frequency range from 1 Hz to 10 Hz.
基金Project supported by the National Key Research and Development Program of China(Nos.2019YFE0192600,2017YFE0132000,and 2019YFB1503700)the National Natural Science Foundation of China(Nos.51761135012 and 11872248)。
文摘In a large wind farm,the wakes of upstream and downstream wind turbines can interfere with each other,affecting the overall power output of the wind farm.To further improve the numerical accuracy of the turbine wake dynamics under atmosphere turbulence,this work proposes some improvements to the actuator line-large-eddy simulation(AL-LES)method.Based on the dynamic k-equation large-eddy simulation(LES),this method uses a precursor method to generate atmospheric inflow turbulence,models the tower and nacelle wakes,and improves the body force projection method based on an anisotropic Gaussian distribution function.For these three improvements,three wind tunnel experiments are used to validate the numerical accuracy of this method.The results show that the numerical results calculated in the far-wake region can reflect the characteristics of typical onshore and offshore wind conditions compared with the experimental results.After modeling the tower and nacelle wakes,the wake velocity distribution is consistent with the experimental result.The radial migration velocity of the tip vortex calculated by the improved blade body force distribution model is 0.32 m/s,which is about 6%different from the experimental value and improves the prediction accuracy of the tip vortex radial movement.The method proposed in this paper is very helpful for wind turbine wake dynamic analysis and wind farm power prediction.
基金Supported by the National Natural Science Foundation of China (50606026, 50736006)the Foundation of State Key Laboratory of Engines, Tianjin University (K-2010-07)
文摘Spray combustion is widely used in power, transportation, chemical and metallurgical, iron and steel making, aeronautical and astronautical engineering. In recent years, large-eddy simulation (LES) becomes more and more attractive, because it can give the instantaneous flow and flame structures, and may give more accurate statistical results than the Reynolds averaged Navier-Stokes (RANS) modeling. In this paper, the present status of the studies on LES of spray combustion is reviewed, and the future research needs are discussed.
基金funded jointly by the National Basic Research Program of China(″973″Program)(No.2014CB046200)the Jiangsu Provincial Natural Science Foundation(No.BK20140059)+2 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe National Natural Science Foundation of China(No.11172135)the EU Seventh Framework Program(No.FP7-PEOPLE-2010-IRSES-269202)
文摘A hybrid method is presented to numerically investigate the wind turbine aerodynamic characteristics.The wind turbine blade is replaced by an actuator line model.Turbulence is treated using a dynamic one-equation subgrid-scale model in large eddy simulation.Detailed information on the basic characteristics of the wind turbine wake is obtained and discussed.The rotor aerodynamic performance agrees well with the measurements.The actuator line method large-eddy simulation(ALM-LES)technique demonstrates its high potential in providing accurate load prediction and high resolution of turbulent fluctuations in the wind turbine wakes and the interactions within a feasible cost.
基金Supported by the National Key Research and Development Program of China(Nos.2016YFC1401404,2017YFA0604102)the National Natural Science Foundation of China(Nos.41506015,41576013)+1 种基金the Zhejiang Provincial Natural Science Foundation(No.LY16D060001)the Open Research Fund of the State Key Laboratory of Estuarine and Coastal Research(No.SKLEC-KF201406)
文摘Oceanic turbulence plays an important role in coastal flow. However, as the effect of an uneven lower boundary on the adjacent turbulence is still not well understood, we explore the mechanics of nearshore turbulence with a turbulence-resolving numerical model known as a large-eddy-simulation model for an idealized scenario in a coastal region for which the lower boundary is a solid sinusoidal wave. The numerical simulation demonstrates how the mechanical energy of the current is transferred into local turbulence mixing, and shows the changes in turbulent intensity over the continuous phase change of the lower topography. The strongest turbulent kinetic energy is concentrated above the trough of the wavy surface. The turbulence mixing is mainly generated by the shear forces; the magnitude of shear production has a local maximum over the crest of the seabed topography, and there is an asymmetry in the shear production between the leeward and windward slopes. The numerical results are consistent with results from laboratory experiments. Our analysis provides an important insight into the mechanism of turbulent kinetic energy production and development.
基金Supported by the National Natural Science Foundation of China(5073600,51266008)the Research Grant Council of Hong Kong(5105/08E,B-Q10H)
文摘Large-eddy simulation of spray combustion is under its rapid development.Different combustion models were used by different investigators.However,these models are less validated by detailed experimental data.In this paper,large-eddy simulation(LES)of ethanol spray-air combustion was made using an Eulerian-Lagrangian approach,a subgrid-scale kinetic energy stress model,and a filtered finite-rate combustion model,neglecting the sub-grid scale reaction rate.The simulation results are compared with experimental dada in the literature and validated in detail.The LES obtained statistically averaged gas temperature is in much better agreement with the experimental results than Reynolds averaged(RANS)modeling using the most complex probability density function(PDF)equation combustion model.The instantaneous LES results show the coherent structures of the shear region near the high-temperature flame zone and the fuel vapor concentration map,indicating that the droplets are concentrated in this shear region.The instantaneous temperature,oxygen and carbon dioxide concentration maps show the close interaction between the coherent structures and the combustion reaction.
