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-   -   Reg. CEL for user-defined boundary condition (http://www.cfd-online.com/Forums/cfx/121477-reg-cel-user-defined-boundary-condition.html)

nvarma July 29, 2013 16:09

Reg. CEL for user-defined boundary condition
 
Hello,

You don't have to read the entire explanation to answer the query. You can go to the Questions at the bottom.

So I have to model a one way valve as a part of a much larger simulation. I was trying to model this by specifying boundary condition which would turn the "interface" into a wall in case pressure difference across is -ve and turn it into an interface(allowing flow) if pressure difference across is +ve (valve open).

Since it is a transient simulation and takes a lot of time, I don't want to physically model the valve, but at the same time avoid backflows that might be unrealistic.

I did read through the manual carefully, but I might have skipped through a lot of pages(it's too long).

So here are my questions:

>> How can I access the Pressure on both sides of a "surface" in CFX through expressions: any link to the syntax would do?
>> What is the best(fastest) way to average and compare the pressure on both sides of a surface?
>>Is there a way to change an interface into a "wall" allowing no normal flow during the simulation, and back?

Thank you very much. Any suggestions or comments appreciated.

ghorrocks July 29, 2013 23:02

I would implement your valve using an interface with a define a conditional connection control to close and open it. I would use a function like areaAve(u velocity)@interface (assuming the flow is in the x direction at the valve) and if >0 then open it and if <0 then close it. Should be easy.

nvarma July 30, 2013 12:08

Thanks, I will try that.
But in the previous simulations, the flow profile varies across the cross section of the wall. i.e even though the average velocity is positive ,there are backflow at different parts, which is what I want to avoid.

ghorrocks July 30, 2013 20:06

I used the areaAve function. That means if the area average velocity over the valve is forward the entire thing will be open, otherwise it will be entirely closed. This approach cannot result in it being partially open.


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