A general framework for the development of high-order compact schemes has been proposed recently.The core steps of the schemes are composed of the following.1).Based on a kinetic model equation,from a generalized init...A general framework for the development of high-order compact schemes has been proposed recently.The core steps of the schemes are composed of the following.1).Based on a kinetic model equation,from a generalized initial distribution of flow variables construct a time-accurate evolution solution of gas distribution function at a cell interface and obtain the corresponding flux function;2).Introduce the WENO-type weighting functions into the high-order time-derivative of the cell interface flux function in the multistage multi-derivative(MSMD)time stepping scheme to cope with the possible impingement of a shock wave on a cell interface within a time step,and update the cell-averaged conservative flow variables inside each control volume;3).Model the time evolution of the gas distribution function on both sides of a cell interface separately,take moments of the inner cell interface gas distribution function to get flow variables,and update the cell-averaged gradients of flow variables inside each control volume;4).Based on the cell-averaged flow variables and their gradients,develop compact initial data reconstruction to get initial condition of flow distributions at the beginning of next time step.A compact gas-kinetic scheme(GKS)up to sixth-order accuracy in space and fourth-order in time has been constructed on 2D unstructured mesh.In this paper,the compact GKS up to fourth-order accuracy on three-dimensional tetrahedral mesh will be further constructed with the focus on the WENO-type initial compact data reconstruction.Nonlinear weights are designed to achieve high-order accuracy for the smooth Navier-Stokes solution and keep super robustness in 3D computation with strong shock interactions.The fourth-order compact GKS uses a large time step with a CFL number 0.6 in the simulations from subsonic to hypersonic flow.A series of test cases are used to validate the scheme.The high-order compact GKS can be used in 3D applications with complex geometry.展开更多
In this paper,a class of compact higher-order gas-kinetic schemes(GKS)with spectrallike resolution will be presented.Based on the high-order gas evolution model,both the flux function and conservative flow variables ...In this paper,a class of compact higher-order gas-kinetic schemes(GKS)with spectrallike resolution will be presented.Based on the high-order gas evolution model,both the flux function and conservative flow variables in GKS can be evaluated explicitly from the time-accurate gas distribution function at a cell interface.As a result,inside each control volume both the cell-averaged flow variables and their cell-averaged gradients can be updated within each time step.The flow variable update and slope update are coming from the same physical solution at the cell interface.This strategy needs time accurate solution at a cell interface,which cannot be achieved by the Riemann problem based flow solvers,even though they can also provide the interface flux functions and interface flow variables.Instead,in order to update the slopes in the Riemann-solver based schemes,such as HWENO,there are additional governing equations for slopes or equivalent degrees of freedom inside each cell.In GKS,only a single time accurate gas evolution model is needed at the cell interface for updating cell averaged flow variables through interface fluxes and updating the cell averaged slopes through the interface flow variables.Based on both cell averaged values and their slopes,compact 6th-order and 8th-order linear and nonlinear reconstructions can be developed.As analyzed in this paper,the local linear compact reconstruction without limiter can achieve a spectral-like resolution at large wavenumber than the well-established compact scheme of Lele with globally coupled flow variables and their derivatives.For nonlinear gas dynamic evolution,in order to avoid spurious oscillation in discontinuous region,the above compact linear reconstruction from the symmetric stencil can be divided into sub-stencils and apply a biased nonlinear WENO-Z reconstruction.Consequently discontinuous solutions can be captured through the 6th-order and 8th-order compact WENO-type nonlinear reconstruction.In GKS,the time evolution solution of the gas distribution function at a cell interface is based on an integral solution of the kinetic model equation,which covers a physical process from an initial non-equilibrium state to a final equilibrium one.Since the initial non-equilibrium state is obtained based on the nonlinear WENO-Z reconstruction,and the equilibrium state is basically constructed from the linear symmetric reconstruction,the GKS evolution models unifies the nonlinear and linear reconstructions in a gas relaxation process in the determination of a time-dependent gas distribution function.This property gives GKS great advantages in capturing both discontinuous shock waves and the linear aero-acoustic waves in a single computation due to its dynamical adaptation of non-equilibrium and equilibrium states in different flow regions.This dynamically adaptive model helps to solve a long lasting problem in the development of high-order schemes about the choices of the linear and nonlinear reconstructions.Compared with discontinuous Galerkin(DG)scheme,the current compact GKS uses the same local and compact stencil,achieves the 6th-order and 8th-order accuracy,uses a much larger time step with CFL number≥0.3,has the robustness as a 2nd-order scheme,and gets accurate solutions in both shock and smooth regions without introducing trouble cell and additional limiting process.The nonlinear reconstruction in the compact GKS is solely based on the WENO-Z technique.At the same time,the current scheme solves the Navier-Stokes equations automatically due to combined inviscid and viscous flux terms from a single time evolution gas distribution function at a cell interface.Due to the use of multi-stage multi-derivative(MSMD)time-stepping technique,for achieving a 4th-order time accuracy,the current scheme uses only two stages instead of four in the traditional Runge-Kutta method.As a result,the current GKS becomes much more efficient than the corresponding same order DG method.A variety of numerical tests are presented to validate the compact 6th and 8th-order GKS.The current scheme presents a state-of-art numerical solutions under a wide range of flow conditions,i.e.,strong shock discontinuity,shear instability,aero-acoustic wave propagation,and NS solutions.It promotes the development of high-order scheme to a new level of maturity.The success of the current scheme crucially depends on the high-order gas evolution model,which cannot be achieved by any other approach once the 1st-order Riemann flux function is still used in the development of high-order numerical algorithms.展开更多
The virome is the most abundant and highly variable microbial consortium in the gut.Because of difficulties in isolating and culturing gut viruses and the lack of reference genomes,the virome has remained a rela-tivel...The virome is the most abundant and highly variable microbial consortium in the gut.Because of difficulties in isolating and culturing gut viruses and the lack of reference genomes,the virome has remained a rela-tively elusive aspect of the human microbiome.In recent years,studies on the virome have accumulated growing evidence showing that the virome is diet-modulated and widely involved in regulating health.Here,we review the responses of the gut virome to dietary intake and the potential health implications,presenting changes in the gut viral community and preferences of viral members to particular diets.We further discuss how viral-bacterial interactions and phage lifestyle shifts shape the gut microbiota.We also discuss the specific functions conferred by diet on the gut virome and bacterial community in the context of horizontal gene transfer,as well as the import of new viral members along with the diet.Collating these studies will expand our understanding of the dietary regulation of the gut virome and inspire dietary in-terventions and health maintenance strategies targeting the gut microbiota.展开更多
基金the National Natural Science Foundation of China(No.12172316)Hong Kong research grant council 16208021 and 16301222CORE as a joint research centre for ocean research between QNLM and HKUST through the project QNLM20SC01-A and QNLM20SC01-E.
文摘A general framework for the development of high-order compact schemes has been proposed recently.The core steps of the schemes are composed of the following.1).Based on a kinetic model equation,from a generalized initial distribution of flow variables construct a time-accurate evolution solution of gas distribution function at a cell interface and obtain the corresponding flux function;2).Introduce the WENO-type weighting functions into the high-order time-derivative of the cell interface flux function in the multistage multi-derivative(MSMD)time stepping scheme to cope with the possible impingement of a shock wave on a cell interface within a time step,and update the cell-averaged conservative flow variables inside each control volume;3).Model the time evolution of the gas distribution function on both sides of a cell interface separately,take moments of the inner cell interface gas distribution function to get flow variables,and update the cell-averaged gradients of flow variables inside each control volume;4).Based on the cell-averaged flow variables and their gradients,develop compact initial data reconstruction to get initial condition of flow distributions at the beginning of next time step.A compact gas-kinetic scheme(GKS)up to sixth-order accuracy in space and fourth-order in time has been constructed on 2D unstructured mesh.In this paper,the compact GKS up to fourth-order accuracy on three-dimensional tetrahedral mesh will be further constructed with the focus on the WENO-type initial compact data reconstruction.Nonlinear weights are designed to achieve high-order accuracy for the smooth Navier-Stokes solution and keep super robustness in 3D computation with strong shock interactions.The fourth-order compact GKS uses a large time step with a CFL number 0.6 in the simulations from subsonic to hypersonic flow.A series of test cases are used to validate the scheme.The high-order compact GKS can be used in 3D applications with complex geometry.
基金The current research is supported by Hong Kong research grant council(16206617)and National Science Foundation of China(11772281,91852114,11701038).
文摘In this paper,a class of compact higher-order gas-kinetic schemes(GKS)with spectrallike resolution will be presented.Based on the high-order gas evolution model,both the flux function and conservative flow variables in GKS can be evaluated explicitly from the time-accurate gas distribution function at a cell interface.As a result,inside each control volume both the cell-averaged flow variables and their cell-averaged gradients can be updated within each time step.The flow variable update and slope update are coming from the same physical solution at the cell interface.This strategy needs time accurate solution at a cell interface,which cannot be achieved by the Riemann problem based flow solvers,even though they can also provide the interface flux functions and interface flow variables.Instead,in order to update the slopes in the Riemann-solver based schemes,such as HWENO,there are additional governing equations for slopes or equivalent degrees of freedom inside each cell.In GKS,only a single time accurate gas evolution model is needed at the cell interface for updating cell averaged flow variables through interface fluxes and updating the cell averaged slopes through the interface flow variables.Based on both cell averaged values and their slopes,compact 6th-order and 8th-order linear and nonlinear reconstructions can be developed.As analyzed in this paper,the local linear compact reconstruction without limiter can achieve a spectral-like resolution at large wavenumber than the well-established compact scheme of Lele with globally coupled flow variables and their derivatives.For nonlinear gas dynamic evolution,in order to avoid spurious oscillation in discontinuous region,the above compact linear reconstruction from the symmetric stencil can be divided into sub-stencils and apply a biased nonlinear WENO-Z reconstruction.Consequently discontinuous solutions can be captured through the 6th-order and 8th-order compact WENO-type nonlinear reconstruction.In GKS,the time evolution solution of the gas distribution function at a cell interface is based on an integral solution of the kinetic model equation,which covers a physical process from an initial non-equilibrium state to a final equilibrium one.Since the initial non-equilibrium state is obtained based on the nonlinear WENO-Z reconstruction,and the equilibrium state is basically constructed from the linear symmetric reconstruction,the GKS evolution models unifies the nonlinear and linear reconstructions in a gas relaxation process in the determination of a time-dependent gas distribution function.This property gives GKS great advantages in capturing both discontinuous shock waves and the linear aero-acoustic waves in a single computation due to its dynamical adaptation of non-equilibrium and equilibrium states in different flow regions.This dynamically adaptive model helps to solve a long lasting problem in the development of high-order schemes about the choices of the linear and nonlinear reconstructions.Compared with discontinuous Galerkin(DG)scheme,the current compact GKS uses the same local and compact stencil,achieves the 6th-order and 8th-order accuracy,uses a much larger time step with CFL number≥0.3,has the robustness as a 2nd-order scheme,and gets accurate solutions in both shock and smooth regions without introducing trouble cell and additional limiting process.The nonlinear reconstruction in the compact GKS is solely based on the WENO-Z technique.At the same time,the current scheme solves the Navier-Stokes equations automatically due to combined inviscid and viscous flux terms from a single time evolution gas distribution function at a cell interface.Due to the use of multi-stage multi-derivative(MSMD)time-stepping technique,for achieving a 4th-order time accuracy,the current scheme uses only two stages instead of four in the traditional Runge-Kutta method.As a result,the current GKS becomes much more efficient than the corresponding same order DG method.A variety of numerical tests are presented to validate the compact 6th and 8th-order GKS.The current scheme presents a state-of-art numerical solutions under a wide range of flow conditions,i.e.,strong shock discontinuity,shear instability,aero-acoustic wave propagation,and NS solutions.It promotes the development of high-order scheme to a new level of maturity.The success of the current scheme crucially depends on the high-order gas evolution model,which cannot be achieved by any other approach once the 1st-order Riemann flux function is still used in the development of high-order numerical algorithms.
基金This work was supported by the National Key Research and Development Program of China(2022YFA1304102)the National Natural Science Foundation of China(32070122,32370053,T2341010)+2 种基金the Chinese Universities Scientific Fund(2023RC022)Pinduoduo-Chinaa Agricultural University Research Fund(PC2023B02015)the 2115 Talent Development Program of China Agricultural University.
文摘The virome is the most abundant and highly variable microbial consortium in the gut.Because of difficulties in isolating and culturing gut viruses and the lack of reference genomes,the virome has remained a rela-tively elusive aspect of the human microbiome.In recent years,studies on the virome have accumulated growing evidence showing that the virome is diet-modulated and widely involved in regulating health.Here,we review the responses of the gut virome to dietary intake and the potential health implications,presenting changes in the gut viral community and preferences of viral members to particular diets.We further discuss how viral-bacterial interactions and phage lifestyle shifts shape the gut microbiota.We also discuss the specific functions conferred by diet on the gut virome and bacterial community in the context of horizontal gene transfer,as well as the import of new viral members along with the diet.Collating these studies will expand our understanding of the dietary regulation of the gut virome and inspire dietary in-terventions and health maintenance strategies targeting the gut microbiota.
