# Non-reflective boundary condition

I'm currently solving incompressible Navier-Stokes system of equations with periodic flow and high viscosity.

Is there any outlet boundary types that avoids the reflection of flow from the outlet back into the computational domain? (Neumann is not sufficient).

Update:

Left: $$u = C sin (\alpha y + \beta t) + u_0$$

Top: open

Bot: wall

Right: open

• Have a look at complex absorbing potentials. Sep 19 '21 at 22:53
• Can you write down your PDE? Sep 19 '21 at 23:02
• It crucially depends on what your PDE is. You probably want to state the model you're using for your flow. Sep 19 '21 at 23:06
• If you have periodic inlet it means that the (velocity) function is periodic in your domain, so it should be the same that you get in the outlet, doesn't it? Sep 20 '21 at 20:06
• I give up. You only provided half of the information requested. You don't say what "open boundary" is supposed to mean, you don't say what "wall" is supposed to mean mathematically, you don't show a picture, and you provide a boundary condition for the left boundary that only provides a scalar when the N-S equations require you to provide the full velocity vector. People here can't be expected to keep asking questions if you want to get an answer to your post. Sep 21 '21 at 4:17