COMSOL doing periodic boundary conditions in navier stokes

[jwq]

Please can anyone tell me how to set this up?

I know how to do the required settings in the Physics/Period Conditions.

However, to fully implement it, I'm also required to choose boundary conditions in the 2D incompressible navier stokes solver (e.g. wall, inlet, outflow, open boundary, stress etc). Which one shall i choose?

(According to Zimmerman's comsol textbook, it should be "Ouflow/pressure". However he's using comsol 3.2. I'm using 3.5, and this option is not available in mine. The nearest matches are "outlet/pressure" and "outlet/pressure, no viscous stress". Both of these of these require that i set a value for the pressure on each outlet boundary, which doesn't make sense to me. Setting outlet pressure values is not even mentioned in Zimmerman's book, so i assume in comsol 3.2 there's no need to in order to set up periodicity.)

 

[Aaron Bex]

The best approach for setting up periodicity in COMSOL 3.5 is to use the Outlet/Pressure, No Viscous Stress boundary condition. This boundary condition does require that you set a Pressure value on each outlet boundary, but it will not affect the periodicity. The Pressure values are typically set to be the same on all outlets, but the exact value is not important.

 

[oswaler]

I understand the frustration of trying to figure out the proper settings for a simulation. In regards to periodic boundary conditions in Navier-Stokes equations, it is important to first determine the type of flow you are trying to simulate. Is it laminar or turbulent? Steady or unsteady? These factors will affect the boundary conditions you need to choose.

In COMSOL, the "outlet/pressure" and "outlet/pressure, no viscous stress" options are both valid choices for periodic boundary conditions in Navier-Stokes equations. However, the difference between the two options lies in the type of flow being simulated. The "outlet/pressure" option is more suitable for steady-state, laminar flow while the "outlet/pressure, no viscous stress" option is better for unsteady or turbulent flow.

In terms of setting a value for outlet pressure, this is necessary for the solver to calculate the correct flow behavior. It may not have been mentioned in Zimmerman's book because it is assumed that the user understands the basic principles of fluid mechanics and knows how to determine appropriate outlet pressure values for their specific simulation.

I would recommend consulting the COMSOL documentation or reaching out to their technical support team for further guidance on setting up periodic boundary conditions in Navier-Stokes equations in version 3.5. They may have updated the options or have additional information on how to properly set up the simulation. Additionally, it may be helpful to review the physics behind periodic boundary conditions and how they affect the solution of the Navier-Stokes equations.