[sanjaypatle]

I have only inlet boundary expressions which are time dependent and other boundaries are open, sidewalls, bottom wall and outlet, then how write expression for outlet pressure? Please keep it mind that pressure at outlet will not be zero.

[sanjaypatle]

I used Ansys-cfx tool

[Opaque]

Originally Posted by sanjaypatle

I have only inlet boundary expressions which are time dependent and other boundaries are open, sidewalls, bottom wall and outlet, then how write expression for outlet pressure? Please keep it mind that pressure at outlet will not be zero.

I imagine you know the variation you would like to see -> it is a BC.

Have you done the free surface modeling tutorial?

[sanjaypatle]

Yes I did surface flow simulation (steady case) using Ansys-cfx

[ghorrocks]

Doesn't that tutorial example show you how to implement a boundary condition by CEL?77

[sanjaypatle]

I know how to write CEL expression. But I don't have velocity and depth data for outlet boundary and other boundaries are set. I want outlet pressure and water volume fraction for outlet for transient multiphase open channel flow.
Inlet boundary expressions are, massflowrate and AVFinlet, WVFinlet.

[sanjaypatle]

Here AVFinlet means air volume fraction at inlet and Wvfinlet means water volume fraction at inlet. I am doing multiphase transient simulation in open channel for fast flowing floods. I have inlet boundaries only, then I how set outlet boundary in ansys-cfx.
I define user function and expression at inlet for mass flow rate and pressure(time dependent). I need values for outlet only, how set it without velocity and depth .

[ghorrocks]

You have to know something at the exit boundary so you can define a boundary condition. If you do not know anything at your proposed boundary you cannot use it and must move it to another location where you do know the conditions.

Maybe you should add a basin to collect the flow and you can put a boundary on that.

[sanjaypatle]

It is mandatory Boundary (Outlet) and our case of unsteady flow. So I am looking for wright approach to simulate this open channel multiphase transient flow problem.

[Opaque]

Originally Posted by sanjaypatle

It is mandatory Boundary (Outlet) and our case of unsteady flow. So I am looking for wright approach to simulate this open channel multiphase transient flow problem.

Your model is part of a larger system, correct? If the open channel connects to other parts upstream and downstream, you must know something about those parts.

In the simple cases of open channel flow I did 30+ years ago, I recall I always had the depth (pressure either static or total).

You cannot try to model something w/o knowing the states upstream and downstream.

[sanjaypatle]

Ok..I will try