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-   -   transient boundary condition(Transient profile) (http://www.cfd-online.com/Forums/cfx/88915-transient-boundary-condition-transient-profile.html)

kmgraju May 30, 2011 11:58

transient boundary condition(Transient profile)
 
Dear friends

I have questions on transient boundary condition

"In some cases boundary conditions arise from measurements or mathematical functions".
My questions are :

1. Is it possible to calculate the mean value of the measurements or mathematical function at the inlet and middle of the fluid model?

2. If the inlet is transient ( example: pressure) , How to set up the outlet condition? (example : Mass flow rate). Will the outlet boundary condition (Mass flow rate) be a function or Number?

Thank you


Regards
Govind

ghorrocks May 30, 2011 20:20

Q1: Yes, this is possible
Q2: You set the boundary conditions to match what you are modelling.

kmgraju May 30, 2011 22:29

transient analysis
 
Quote:

Originally Posted by ghorrocks (Post 309835)
Q1: Yes, this is possible
Q2: You set the boundary conditions to match what you are modelling.

Dear friend

Thanks for your kind reply

Can you please explain how to calculate the average value (example: Pressure) at the inlet or middle of the fluid model.

2. For example, I set step pulse pressure at the inlet and I set a function at the outlet ( example sinusoidal Mass flow rate or sinusoidal velocity) , How will this match?

Thanks you


Regards

Govind

ghorrocks May 31, 2011 08:23

Use a CEL expression like areaAve(p)@inlet.

What do you mean by match? As it converges it will reduce the imbalances. If incompressible that means flow in equals flow out, regardless or pressure or flow rate.

kmgraju June 2, 2011 21:41

transient analysis
 
Quote:

Originally Posted by ghorrocks (Post 309942)
Use a CEL expression like areaAve(p)@inlet.

What do you mean by match? As it converges it will reduce the imbalances. If incompressible that means flow in equals flow out, regardless or pressure or flow rate.

Dear friend
My fluid flow is pulsatile flow. mean flow rate is 50ml/min. Density is 1040 kg/m^3 . The mass flow rate = density*flow rate. How do I give this pulsatile mass flow rate value at the outlet.

Thank you

Regards
Govind

ghorrocks June 2, 2011 23:17

Use a CEL expression like if or step, or a 1D interpolation function. Then use the function/expression in the boundary condition.

kmgraju June 3, 2011 00:22

transient analysis
 
Quote:

Originally Posted by ghorrocks (Post 310326)
Use a CEL expression like if or step, or a 1D interpolation function. Then use the function/expression in the boundary condition.

Dear friend

How do I know the flow rate expression/function at the outlet?. I know average flow rate is 50ml/min

Thank you
Govind

ghorrocks June 3, 2011 07:10

Is this an external input, that is you specify the flow rate; or is this an output of the simulation?


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