Multiscale mixing of the turbine blade tip leakage and mainstream flows causes considerable aerodynamic loss.Understanding it is crucial to correctly estimating the mixing loss and thus improving the turbine's per...Multiscale mixing of the turbine blade tip leakage and mainstream flows causes considerable aerodynamic loss.Understanding it is crucial to correctly estimating the mixing loss and thus improving the turbine's performance.The multiscale mixing phenomenon in a typical high-pressure turbine rotor flow was studied in this work.The contributions of various scale flows to entropy production and mixing properties were identified.The corresponding physical mechanisms at different scales were explored.It is shown that the large-scale and time-averaged flow contributions to mixing are significant,accounting for approximately 37.1% and 25% of the total.Time-averaged and large-scale flows cause the majority of the fluid deformation of the material surface,while mesoand small-scale flows just generate finer deformations.It raises the area stretch coefficient and the virtual concentration gradient.Thus,mixing is enhanced.Furthermore,time-averaged and large-scale flows account for the majority of the losses in the upstream and downstream regions of the blade tip respectively,accounting for approximately 53.8%and 33.5%of the total.The sheet-like structures—rather than the tip leaking vortex—are the primary source of the loss.High-dissipation regions are produced by the sheet-like structures via the pressure Hessian term and the self-amplification terms.展开更多
Multiscale gas flows appear in many fields and have received particular attention in recent years.It is challenging to model and simulate such processes due to the large span of temporal and spatial scales.The discret...Multiscale gas flows appear in many fields and have received particular attention in recent years.It is challenging to model and simulate such processes due to the large span of temporal and spatial scales.The discrete unified gas kinetic scheme(DUGKS)is a recently developed numerical approach for simulating multiscale flows based on kinetic models.The finite-volume DUGKS differs from the classical kinetic methods in the modeling of gas evolution and the reconstruction of interface flux.Particularly,the distribution function at a cell interface is reconstructed from the characteristic solution of the kinetic equation in space and time,such that the particle transport and collision effects are coupled,accumulated,and evaluated in a numerical time step scale.Consequently,the cell size and time step of DUGKS are not passively limited by the particle mean-free-path and relaxation time.As a result,the DUGKS can capture the flow behaviors in all regimes without resolving the kinetic scale.Particularly,with the variation of the ratio between numerical mesh size scale and kinetic mean free path scale,the DUGKS can serve as a self-adaptive multiscale method.The DUGKS has been successfully applied to a number of flow problems with multiple flow regimes.This paper presents a brief review of the progress of this method.展开更多
An implicit discrete unified gas kinetic scheme(DUGKS)is developed for multiscale steady flows of binary gas mixtures by solving the Andries-Aoki-Perthame kinetic model(AAP).To ensure the high convergence efficiency f...An implicit discrete unified gas kinetic scheme(DUGKS)is developed for multiscale steady flows of binary gas mixtures by solving the Andries-Aoki-Perthame kinetic model(AAP).To ensure the high convergence efficiency for all flow regimes,the microscopic and macroscopic asynchronous iterative strategies are used,where both the macroscopic and microscopic equations are solved iteratively by the LowerUpper Symmetric Gauss-Seidel(LU-SGS)method.The macroscopic iteration is conducted to solve the macroscopic governing equations containing source terms as an implicit prediction step to evaluate the local equilibrium state of the microscopic evolution,and the macroscopic flux used in the macroscopic iteration is obtained by taking moments of the distribution function.Besides,to keep the asymptotic preserving properties,the numerical flux across the cell interface is reconstructed by the characteristic solution of the kinetic governing equations for both species like the explicit DUGKS for a single gas.Several numerical tests,including the Couette flow,the lid-driven cavity flow,and the flows through a slit of different mixtures,are simulated to verify the accuracy and efficiency of the present scheme for binary mixtures.Furthermore,compared to the explicit DUGKS,the implicit scheme improves the computational efficiency by 1-2 orders of magnitude.展开更多
The unified stochastic particle method based on the Bhatnagar-Gross-Krook model(USP-BGK)has been proposed recently to overcome the low accuracy and efficiency of the traditional stochastic particle methods,such as the...The unified stochastic particle method based on the Bhatnagar-Gross-Krook model(USP-BGK)has been proposed recently to overcome the low accuracy and efficiency of the traditional stochastic particle methods,such as the direct simulation Monte Carlo(DSMC)method,for the simulation of multi-scale gas flows.However,running with extra virtual particles and space interpolation,the previous USP-BGK method cannot be directly transplanted into the existing DSMC codes.In this work,the implementation of USP-BGK is simplified using new temporal evolution and spatial reconstruction schemes.As a result,the present algorithm of the USP-BGK method is similar to the DSMC method and can be implemented efficiently based on any existing DSMC codes just by modifying the collision module.展开更多
基金supported by the National Science and Technology Major Project,China(No.J2019-Ⅱ-0012-0032)。
文摘Multiscale mixing of the turbine blade tip leakage and mainstream flows causes considerable aerodynamic loss.Understanding it is crucial to correctly estimating the mixing loss and thus improving the turbine's performance.The multiscale mixing phenomenon in a typical high-pressure turbine rotor flow was studied in this work.The contributions of various scale flows to entropy production and mixing properties were identified.The corresponding physical mechanisms at different scales were explored.It is shown that the large-scale and time-averaged flow contributions to mixing are significant,accounting for approximately 37.1% and 25% of the total.Time-averaged and large-scale flows cause the majority of the fluid deformation of the material surface,while mesoand small-scale flows just generate finer deformations.It raises the area stretch coefficient and the virtual concentration gradient.Thus,mixing is enhanced.Furthermore,time-averaged and large-scale flows account for the majority of the losses in the upstream and downstream regions of the blade tip respectively,accounting for approximately 53.8%and 33.5%of the total.The sheet-like structures—rather than the tip leaking vortex—are the primary source of the loss.High-dissipation regions are produced by the sheet-like structures via the pressure Hessian term and the self-amplification terms.
基金Z.L.Guo is supported by the National Natural Science Foundation of China(51836003,11872024)the National Numerical Wind Tunnel project(NNW2019-JT01-016)+1 种基金the Fundamental Research Funds for the Central Universities(2019kfyXMBZ040)K.Xu is supported by the National Natural Science Foundation of China(11772281,91852114).
文摘Multiscale gas flows appear in many fields and have received particular attention in recent years.It is challenging to model and simulate such processes due to the large span of temporal and spatial scales.The discrete unified gas kinetic scheme(DUGKS)is a recently developed numerical approach for simulating multiscale flows based on kinetic models.The finite-volume DUGKS differs from the classical kinetic methods in the modeling of gas evolution and the reconstruction of interface flux.Particularly,the distribution function at a cell interface is reconstructed from the characteristic solution of the kinetic equation in space and time,such that the particle transport and collision effects are coupled,accumulated,and evaluated in a numerical time step scale.Consequently,the cell size and time step of DUGKS are not passively limited by the particle mean-free-path and relaxation time.As a result,the DUGKS can capture the flow behaviors in all regimes without resolving the kinetic scale.Particularly,with the variation of the ratio between numerical mesh size scale and kinetic mean free path scale,the DUGKS can serve as a self-adaptive multiscale method.The DUGKS has been successfully applied to a number of flow problems with multiple flow regimes.This paper presents a brief review of the progress of this method.
基金supported by the National Natural Science Foundation of China(Grants No.12002131 and No.11872024)Project funded by China Postdoctoral Science Foundation(No.2020M672347 and No.2021M701565).
文摘An implicit discrete unified gas kinetic scheme(DUGKS)is developed for multiscale steady flows of binary gas mixtures by solving the Andries-Aoki-Perthame kinetic model(AAP).To ensure the high convergence efficiency for all flow regimes,the microscopic and macroscopic asynchronous iterative strategies are used,where both the macroscopic and microscopic equations are solved iteratively by the LowerUpper Symmetric Gauss-Seidel(LU-SGS)method.The macroscopic iteration is conducted to solve the macroscopic governing equations containing source terms as an implicit prediction step to evaluate the local equilibrium state of the microscopic evolution,and the macroscopic flux used in the macroscopic iteration is obtained by taking moments of the distribution function.Besides,to keep the asymptotic preserving properties,the numerical flux across the cell interface is reconstructed by the characteristic solution of the kinetic governing equations for both species like the explicit DUGKS for a single gas.Several numerical tests,including the Couette flow,the lid-driven cavity flow,and the flows through a slit of different mixtures,are simulated to verify the accuracy and efficiency of the present scheme for binary mixtures.Furthermore,compared to the explicit DUGKS,the implicit scheme improves the computational efficiency by 1-2 orders of magnitude.
基金supported by the National Numerical Wind-Tunnel Project(No.NNW2018-ZT3B07)the National Natural Science Foundation of China(No.51506063)Jun Zhang would like to thank the support of the National Natural Science Foundation of China(No.92052104).
文摘The unified stochastic particle method based on the Bhatnagar-Gross-Krook model(USP-BGK)has been proposed recently to overcome the low accuracy and efficiency of the traditional stochastic particle methods,such as the direct simulation Monte Carlo(DSMC)method,for the simulation of multi-scale gas flows.However,running with extra virtual particles and space interpolation,the previous USP-BGK method cannot be directly transplanted into the existing DSMC codes.In this work,the implementation of USP-BGK is simplified using new temporal evolution and spatial reconstruction schemes.As a result,the present algorithm of the USP-BGK method is similar to the DSMC method and can be implemented efficiently based on any existing DSMC codes just by modifying the collision module.
