We establish magnetic diffusion vanishing limit of the nonlinear pipe Magnetohy- drodynamic flow by the mathematical validity of the Prandtl boundary layer theory with fixed viscosity. The convergence is verified unde...We establish magnetic diffusion vanishing limit of the nonlinear pipe Magnetohy- drodynamic flow by the mathematical validity of the Prandtl boundary layer theory with fixed viscosity. The convergence is verified under various Sobolev norms, including the L∞（L2） and L∞（H1） norm.展开更多
The equation arising from Prandtl boundary layer theory (e)u/(e)t-(e)/(e)x1(a(u,x,t)(e)u/(e)xi)-fi(x)Diu+c(x,t)u=g(x,t)is considered.The existence of the entropy solution can be proved by BV estimate method.The intere...The equation arising from Prandtl boundary layer theory (e)u/(e)t-(e)/(e)x1(a(u,x,t)(e)u/(e)xi)-fi(x)Diu+c(x,t)u=g(x,t)is considered.The existence of the entropy solution can be proved by BV estimate method.The interesting problem is that,since a(·,x,t) may be degenerate on the boundary,the usual boundary value condition may be overdetermined.Accordingly,only dependent on a partial boundary value condition,the stability of solutions can be expected.This expectation is turned to reality by Kru(z)kov's bi-variables method,a reasonable partial boundary value condition matching up with the equation is found first time.Moreover,if axi(·,x,t)|x∈(e)Ω=a(·,x,t)|x∈(e)Ω=0 and fi(x)|x∈(e)Ω=0,the stability can be proved even without any boundary value condition.展开更多
By treating eddy viscosity and eddy diffusivity as optimal control parameters, a new method is developed to determine the eddy viscosity, eddy diffusivity and turbulent Prandtl number from first principles without app...By treating eddy viscosity and eddy diffusivity as optimal control parameters, a new method is developed to determine the eddy viscosity, eddy diffusivity and turbulent Prandtl number from first principles without appealing to adjustable empirical constants. The resultant turbulent Prandtl number is compatible with experimental data. This method enables us to estimate the error of Boussinesq’s eddy viscosity (and diffusivity) model and compare various methods of determining eddy transport coefficients.展开更多
The author surveys a few examples of boundary layers for which the Prandtl boundary layer theory can be rigorously validated.All of them are associated with the incompressible Navier-Stokes equations for Newtonian flu...The author surveys a few examples of boundary layers for which the Prandtl boundary layer theory can be rigorously validated.All of them are associated with the incompressible Navier-Stokes equations for Newtonian fluids equipped with various Dirichlet boundary conditions(specified velocity).These examples include a family of(nonlinear 3D) plane parallel flows,a family of(nonlinear) parallel pipe flows,as well as flows with uniform injection and suction at the boundary.We also identify a key ingredient in establishing the validity of the Prandtl type theory,i.e.,a spectral constraint on the approximate solution to the Navier-Stokes system constructed by combining the inviscid solution and the solution to the Prandtl type system.This is an additional difficulty besides the wellknown issue related to the well-posedness of the Prandtl type system.It seems that the main obstruction to the verification of the spectral constraint condition is the possible separation of boundary layers.A common theme of these examples is the inhibition of separation of boundary layers either via suppressing the velocity normal to the boundary or by injection and suction at the boundary so that the spectral constraint can be verified.A meta theorem is then presented which covers all the cases considered here.展开更多
基金supported by Natural Science fund of Henan Province(162300410084)the Key Research Fund of Henan Province(16A110019)+1 种基金BSFC(1132006)CIT&TCD(20130312)
文摘We establish magnetic diffusion vanishing limit of the nonlinear pipe Magnetohy- drodynamic flow by the mathematical validity of the Prandtl boundary layer theory with fixed viscosity. The convergence is verified under various Sobolev norms, including the L∞（L2） and L∞（H1） norm.
基金The paper is supported by Natural Science Foundation of Fujian province(2019J01858)supported by SF of Xiamen University of Technology,China.The author would like to think reviewers for their good comments.
文摘The equation arising from Prandtl boundary layer theory (e)u/(e)t-(e)/(e)x1(a(u,x,t)(e)u/(e)xi)-fi(x)Diu+c(x,t)u=g(x,t)is considered.The existence of the entropy solution can be proved by BV estimate method.The interesting problem is that,since a(·,x,t) may be degenerate on the boundary,the usual boundary value condition may be overdetermined.Accordingly,only dependent on a partial boundary value condition,the stability of solutions can be expected.This expectation is turned to reality by Kru(z)kov's bi-variables method,a reasonable partial boundary value condition matching up with the equation is found first time.Moreover,if axi(·,x,t)|x∈(e)Ω=a(·,x,t)|x∈(e)Ω=0 and fi(x)|x∈(e)Ω=0,the stability can be proved even without any boundary value condition.
基金Project supported by the National Basic Research Program "Non-linear Science" the National Natural Science Foundation of China
文摘By treating eddy viscosity and eddy diffusivity as optimal control parameters, a new method is developed to determine the eddy viscosity, eddy diffusivity and turbulent Prandtl number from first principles without appealing to adjustable empirical constants. The resultant turbulent Prandtl number is compatible with experimental data. This method enables us to estimate the error of Boussinesq’s eddy viscosity (and diffusivity) model and compare various methods of determining eddy transport coefficients.
基金Project supported by the National Science Foundation,the 111 Project from the Ministry of Education of China at Fudan University and the COFRS award from Florida State University
文摘The author surveys a few examples of boundary layers for which the Prandtl boundary layer theory can be rigorously validated.All of them are associated with the incompressible Navier-Stokes equations for Newtonian fluids equipped with various Dirichlet boundary conditions(specified velocity).These examples include a family of(nonlinear 3D) plane parallel flows,a family of(nonlinear) parallel pipe flows,as well as flows with uniform injection and suction at the boundary.We also identify a key ingredient in establishing the validity of the Prandtl type theory,i.e.,a spectral constraint on the approximate solution to the Navier-Stokes system constructed by combining the inviscid solution and the solution to the Prandtl type system.This is an additional difficulty besides the wellknown issue related to the well-posedness of the Prandtl type system.It seems that the main obstruction to the verification of the spectral constraint condition is the possible separation of boundary layers.A common theme of these examples is the inhibition of separation of boundary layers either via suppressing the velocity normal to the boundary or by injection and suction at the boundary so that the spectral constraint can be verified.A meta theorem is then presented which covers all the cases considered here.
