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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Pressure Velocity Couplings

Posted 2010年12月28日 GMT-5 15:24 Computational Fluid Dynamics (CFD) Version 3.5a 2 Replies

Harish Ganapathy
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Hi,

While doing fluid flow modeling (CFD), in softwares like FLUENT which are based on the finite-volume method, we define Pressure-Velocity Couplings like SIMPLE, or PISO etc.

I do not find any information on this in COMSOL though. Can somebody help me out on this ?

Thanks,
Harish
2 Replies Last Post 2011年1月4日 GMT-5 20:05
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2010年12月29日 GMT-5 02:20
Hi

I do not know "fluent" but I'm not sure COMSOl is treating the equations in the same way.

Check the equations in COMSOL for the different physics and modes, and you will see how it's done.

If I remember well "finite volume" it's related to "rho" the density and how invariant you consider it, no ?

--
Good luck
Ivar
Hi I do not know "fluent" but I'm not sure COMSOl is treating the equations in the same way. Check the equations in COMSOL for the different physics and modes, and you will see how it's done. If I remember well "finite volume" it's related to "rho" the density and how invariant you consider it, no ? -- Good luck Ivar
Nathan Lane
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Posted: 1 decade ago 2011年1月4日 GMT-5 20:05

It is likely using a projection strategy very similar to the SIMPLE scheme. Solve the momentum equations with or without pressure (either implicit or explicit) to obtain a predicted velocity. Solve a pressure poisson equation to obtain a pressure correction that can be used to update velocity so that continuity is satisfied. What I would love to know is if they are solving pressure poisson, what, if any boundary conditions are used for this equation.

If you are using v3.5 you will probably see that COMSOL gives several options regarding choice of element. All of these options are now gone in v4.1 in favour of what is likely a stabilised P1P1 element (linear velocity and pressure approximation). Additional stabilisation for the convective terms looks like it is achieved by a streamline upwinding.

Here are a few references that could be a useful starting point if you are looking for more info on solving Incompressible Navier-Stokes with FEM.

(Brooks, Hughes 1982, related to upwinding) Streamline upwind/Petrov-Galerkin formulations for convection dominated flows with particular emphasis on the incompressible Navier-Stokes equations

(Langtangen et. al, 2002, related to NS solution strategies) Numerical Methods for Incompressible Flow

Anything by a guy called Tezduyar, which will probably relate to implementing upwinding strategies.

Anything about equal order elements/circumventing the LBB condition which will talk about additional stabilisation for elements that do not satisfy the LBB condition.
It is likely using a projection strategy very similar to the SIMPLE scheme. Solve the momentum equations with or without pressure (either implicit or explicit) to obtain a predicted velocity. Solve a pressure poisson equation to obtain a pressure correction that can be used to update velocity so that continuity is satisfied. What I would love to know is if they are solving pressure poisson, what, if any boundary conditions are used for this equation. If you are using v3.5 you will probably see that COMSOL gives several options regarding choice of element. All of these options are now gone in v4.1 in favour of what is likely a stabilised P1P1 element (linear velocity and pressure approximation). Additional stabilisation for the convective terms looks like it is achieved by a streamline upwinding. Here are a few references that could be a useful starting point if you are looking for more info on solving Incompressible Navier-Stokes with FEM. (Brooks, Hughes 1982, related to upwinding) Streamline upwind/Petrov-Galerkin formulations for convection dominated flows with particular emphasis on the incompressible Navier-Stokes equations (Langtangen et. al, 2002, related to NS solution strategies) Numerical Methods for Incompressible Flow Anything by a guy called Tezduyar, which will probably relate to implementing upwinding strategies. Anything about equal order elements/circumventing the LBB condition which will talk about additional stabilisation for elements that do not satisfy the LBB condition.

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