Three-dimensional corner separation is a common phenomenon that significantly affects compressor performance. Turbulence model is still a weakness for RANS method on predicting corner separation flow accurately. In th...Three-dimensional corner separation is a common phenomenon that significantly affects compressor performance. Turbulence model is still a weakness for RANS method on predicting corner separation flow accurately. In the present study, numerical study of corner separation in a linear highly loaded prescribed velocity distribution （PVD） compressor cascade has been investigated using seven frequently used turbulence models. The seven turbulence models include Spalart Allmaras model, standard k-e model, realizable k-e model, standard k-to model, shear stress transport k co model, v2-fmodel and Reynolds stress model. The results of these turbulence models have been compared and analyzed in detail with available experimental data. It is found the standard k-1： model, realizable k-e model, v2-f model and Reynolds stress model can provide reasonable results for predicting three dimensional corner separation in the compressor cascade. The Spalart-Allmaras model, standard k-to model and shear stress transport k-w model overesti- mate corner separation region at incidence of 0°. The turbulence characteristics are discussed and turbulence anisotropy is observed to be stronger in the corner separating region.展开更多
In order to gain a better knowledge of the mechanisms and to calibrate computational fluid dynamics （CFD） tools including both Reynolds-averaged Navier-Stokes （RANS） and large eddy simulation （LES）, a detailed a...In order to gain a better knowledge of the mechanisms and to calibrate computational fluid dynamics （CFD） tools including both Reynolds-averaged Navier-Stokes （RANS） and large eddy simulation （LES）, a detailed and accurate experimental study of comer stall in a linear compressor cascade has been carried out. Data are taken at a Reynolds number of 382 000 based on blade chord and inlet velocity. At first, inlet flow boundary layer is surveyed using hot-wire anemometry. Then in order to investigate the effects of incidence, measurements are acquired at five incidences, including static pressures on both blade and endwall sur- faces measured by pressure taps and the total pressure losses of outlet flow measured by a five-hole pressure probe. The maxi- mum losses as well as the extent of losses of the comer stall are presented as a function of the investigated incidences.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
The efficiency and mechanism of an active control device ＂＇Spark Jet＂ and its application in shock-induced separation control are studied using large-eddy simulation in this paper. The base flow is the interaction ...The efficiency and mechanism of an active control device ＂＇Spark Jet＂ and its application in shock-induced separation control are studied using large-eddy simulation in this paper. The base flow is the interaction of an oblique shock-wave generated by 8° wedge and a spatially-developing Ma = 2.3 turbulent boundary layer. The Reynolds number based on the incoming flow property and the boundary layer displacement thickness at the impinging point without shock-wave is 20000. The detailed numerical approaches were presented. The inflow turbulence was generated using the digital filter method to avoid artificial temporal or streamwise periodicity. The , merical results including velocity profile, Reynolds stress profile, skin friction, and wall pressure were sys- tematically validated against the available wind tunnel particle image velocimetry （PIV） measure- ments of the same flow condition. Further study on the control of flow separation due to the strong shock-viscous interaction using an active control actuator ＂＇Spark Jet＇＂ was conducted. The single-pulsed characteristic of the device was obtained and compared with the experiment. Both instantaneous and time-averaged flow fields have shown that the jet flow issuing from the actuator cavity enhances the flow mixing inside the boundary layer, making the boundary layer more resis- tant to flow separation. Skin friction coefficient distribution shows that the separation bubble length is reduced by about 35% with control exerted.展开更多
The influences of the modification of turbulent coherent structures on temperature field and heat transfer in turbulent channel flow are studied using large eddy simulation(LES) of compressible turbulent channel flows...The influences of the modification of turbulent coherent structures on temperature field and heat transfer in turbulent channel flow are studied using large eddy simulation(LES) of compressible turbulent channel flows with spanwise wall oscillation(SWO).The reliability of the LES on such problems is proved by the comparisons of the drag reduction data with those of other researches.The high consistency of coherent velocity structures and temperature structures is found based on the analyses of the turbulent flow field.When the coherent velocity structures are suppressed,the transportations of momentum and heat are reduced simultaneously,demonstrating the same trend.This shows that the turbulent coherent structures have the same effects on the transportations of momentum and heat.The averaged wall heat flux can be reduced with appropriate oscillating parameters.展开更多
Large-eddy simulation（LES） is compared with experiment and Reynolds-averaged Navier-Stokes（RANS）, and LES is shown to be superior to RANS in reproducing corner separation in the LMFA-NACA65 linear compressor casca...Large-eddy simulation（LES） is compared with experiment and Reynolds-averaged Navier-Stokes（RANS）, and LES is shown to be superior to RANS in reproducing corner separation in the LMFA-NACA65 linear compressor cascade, in terms of surface limiting streamlines,blade pressure coefficient, total pressure losses and blade suction side boundary layer profiles. However, LES is too expensive to conduct an influencing parameter study of the corner separation.RANS approach, despite over-predicting the corner separation, gives reasonable descriptions of the corner separated flow, and is thus selected to conduct a parametric study in this paper. Two kinds of influencing parameters on corner separation, numerical and physical parameters, are analyzed and discussed： second order spatial scheme is necessary for a RANS simulation; incidence angle and inflow boundary layer thickness are found to show the most significant influences on the corner separation among the parameters studied; unsteady RANS with the imposed inflow unsteadiness（inflow angle varying sinusoidally with fluctuating amplitude of 0.92°） does not show any non-linear effect on the corner separation.展开更多
In order to study atomization mechanism of a viscoelastic liquid sheet in an electric field, the spatial-temporal stability analysis of a viscoelastic liquid sheet injected into a dielectric station- ary ambient gas i...In order to study atomization mechanism of a viscoelastic liquid sheet in an electric field, the spatial-temporal stability analysis of a viscoelastic liquid sheet injected into a dielectric station- ary ambient gas in the presence of a vertical electric field is conducted. The dispersion relations of both sinuous and varicose disturbance modes are solved to explore the spatial-temporal instability of a charged viscoelastic sheet, by setting both the wave number and frequency complex. A para- metric study is performed to test the influence of the dimensionless parameters on the absolute instability of the sheet. The results show that the increase of liquid Weber number and time constant ratio, or decrease of gas to liquid density ratio and Reynolds number, can damp the absolute insta- bility. The effect of the liquid elasticity depends on the value of time constant ratio： when time con- stant ratio is small, the increase of liquid elasticity could amplify absolute growth rate, but the effect is weak when the elasticity number is relatively large; when time constant ratio is large, the increase of liquid elasticity cannot affect the absolute growth rate. Moreover, the variation of electrical Euler number can hardly influence the absolute instability of a charged viscoelastic sheet.展开更多
基金supported by the National Natural Science Foundation of China(No.51376001,No.51420105008,No.51306013,No.51136003)the National Basic Research Program of China(2012CB720205,2014CB046405)+2 种基金the Beijing Higher Education Young Elite Teacher Projectthe Fundamental Research Funds for the Central Universitiessupported by the Innovation Foundation of BUAA for Ph.D.Graduates
文摘Three-dimensional corner separation is a common phenomenon that significantly affects compressor performance. Turbulence model is still a weakness for RANS method on predicting corner separation flow accurately. In the present study, numerical study of corner separation in a linear highly loaded prescribed velocity distribution （PVD） compressor cascade has been investigated using seven frequently used turbulence models. The seven turbulence models include Spalart Allmaras model, standard k-e model, realizable k-e model, standard k-to model, shear stress transport k co model, v2-fmodel and Reynolds stress model. The results of these turbulence models have been compared and analyzed in detail with available experimental data. It is found the standard k-1： model, realizable k-e model, v2-f model and Reynolds stress model can provide reasonable results for predicting three dimensional corner separation in the compressor cascade. The Spalart-Allmaras model, standard k-to model and shear stress transport k-w model overesti- mate corner separation region at incidence of 0°. The turbulence characteristics are discussed and turbulence anisotropy is observed to be stronger in the corner separating region.
基金National Natural Science Foundation of China(50976010)"111" Project (B08009)
文摘In order to gain a better knowledge of the mechanisms and to calibrate computational fluid dynamics （CFD） tools including both Reynolds-averaged Navier-Stokes （RANS） and large eddy simulation （LES）, a detailed and accurate experimental study of comer stall in a linear compressor cascade has been carried out. Data are taken at a Reynolds number of 382 000 based on blade chord and inlet velocity. At first, inlet flow boundary layer is surveyed using hot-wire anemometry. Then in order to investigate the effects of incidence, measurements are acquired at five incidences, including static pressures on both blade and endwall sur- faces measured by pressure taps and the total pressure losses of outlet flow measured by a five-hole pressure probe. The maxi- mum losses as well as the extent of losses of the comer stall are presented as a function of the investigated incidences.
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supported by the National Natural Science Foundation of China(Nos.11302012,51420105008,51476004,11572025 and 51136003)the National Basic Research Program of China(No.2012CB720205)The computational time for the present study was provided by the UK Turbulence Consortium(EPSRC grant EP/L000261/1)
文摘The efficiency and mechanism of an active control device ＂＇Spark Jet＂ and its application in shock-induced separation control are studied using large-eddy simulation in this paper. The base flow is the interaction of an oblique shock-wave generated by 8° wedge and a spatially-developing Ma = 2.3 turbulent boundary layer. The Reynolds number based on the incoming flow property and the boundary layer displacement thickness at the impinging point without shock-wave is 20000. The detailed numerical approaches were presented. The inflow turbulence was generated using the digital filter method to avoid artificial temporal or streamwise periodicity. The , merical results including velocity profile, Reynolds stress profile, skin friction, and wall pressure were sys- tematically validated against the available wind tunnel particle image velocimetry （PIV） measure- ments of the same flow condition. Further study on the control of flow separation due to the strong shock-viscous interaction using an active control actuator ＂＇Spark Jet＇＂ was conducted. The single-pulsed characteristic of the device was obtained and compared with the experiment. Both instantaneous and time-averaged flow fields have shown that the jet flow issuing from the actuator cavity enhances the flow mixing inside the boundary layer, making the boundary layer more resis- tant to flow separation. Skin friction coefficient distribution shows that the separation bubble length is reduced by about 35% with control exerted.
基金Supported by the Key Subjects of National Natural Science Foundation of China (Grant No. 10732090)the National Natural Science Foundation of China (Grant No. 50476004)the 111 Project (Grant No. B08009)
文摘The influences of the modification of turbulent coherent structures on temperature field and heat transfer in turbulent channel flow are studied using large eddy simulation(LES) of compressible turbulent channel flows with spanwise wall oscillation(SWO).The reliability of the LES on such problems is proved by the comparisons of the drag reduction data with those of other researches.The high consistency of coherent velocity structures and temperature structures is found based on the analyses of the turbulent flow field.When the coherent velocity structures are suppressed,the transportations of momentum and heat are reduced simultaneously,demonstrating the same trend.This shows that the turbulent coherent structures have the same effects on the transportations of momentum and heat.The averaged wall heat flux can be reduced with appropriate oscillating parameters.
基金funded by the Sino-French project AXIOOM (funding: NSFC and ANR)the supports from NSFC (Nos. 51420105008, 51376001, 51506121 and 51676007)performed using HPC resources from GENCICINES (No.2014-2a6081)
文摘Large-eddy simulation（LES） is compared with experiment and Reynolds-averaged Navier-Stokes（RANS）, and LES is shown to be superior to RANS in reproducing corner separation in the LMFA-NACA65 linear compressor cascade, in terms of surface limiting streamlines,blade pressure coefficient, total pressure losses and blade suction side boundary layer profiles. However, LES is too expensive to conduct an influencing parameter study of the corner separation.RANS approach, despite over-predicting the corner separation, gives reasonable descriptions of the corner separated flow, and is thus selected to conduct a parametric study in this paper. Two kinds of influencing parameters on corner separation, numerical and physical parameters, are analyzed and discussed： second order spatial scheme is necessary for a RANS simulation; incidence angle and inflow boundary layer thickness are found to show the most significant influences on the corner separation among the parameters studied; unsteady RANS with the imposed inflow unsteadiness（inflow angle varying sinusoidally with fluctuating amplitude of 0.92°） does not show any non-linear effect on the corner separation.
基金The financial support of the National Natural Science Foundation of China (No. 11302013)
文摘In order to study atomization mechanism of a viscoelastic liquid sheet in an electric field, the spatial-temporal stability analysis of a viscoelastic liquid sheet injected into a dielectric station- ary ambient gas in the presence of a vertical electric field is conducted. The dispersion relations of both sinuous and varicose disturbance modes are solved to explore the spatial-temporal instability of a charged viscoelastic sheet, by setting both the wave number and frequency complex. A para- metric study is performed to test the influence of the dimensionless parameters on the absolute instability of the sheet. The results show that the increase of liquid Weber number and time constant ratio, or decrease of gas to liquid density ratio and Reynolds number, can damp the absolute insta- bility. The effect of the liquid elasticity depends on the value of time constant ratio： when time con- stant ratio is small, the increase of liquid elasticity could amplify absolute growth rate, but the effect is weak when the elasticity number is relatively large; when time constant ratio is large, the increase of liquid elasticity cannot affect the absolute growth rate. Moreover, the variation of electrical Euler number can hardly influence the absolute instability of a charged viscoelastic sheet.
