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-   -   Stagnation pressure (http://www.cfd-online.com/Forums/star-ccm/115074-stagnation-pressure.html)

jackwabbit March 23, 2013 02:38

Stagnation pressure
 
In my simulation of the flow around the Ahmed body to determine drag coefficient, at the front face, I am not getting the expected value of stagnation pressure. Any idea what could be the issue involved?

vangelis March 23, 2013 10:18

what value do you get?
higher or lower than expected?

http://www.cfd-online.com/Forums/ope...-than-one.html

jackwabbit March 23, 2013 13:49

The pressure works out to be 1000 Pa higher than the expected value. What would you recommend for this case specifically since the Ahmed body analysis has been done over so many times. And yes, I'll read on that.

vangelis March 26, 2013 03:41

Try expressing this value as static pressure coefficient.
This value should equal 1 at stagnation point.

jackwabbit March 26, 2013 07:00

I did. But I got a value close to 2 where it was supposed to 1.
My physical conditions with respect to pressure are

Initial conditions
Pressure - 101325 Pa
Reference values
Pressure - 101325 Pa
Force coefficient report
Reference pressure - 101325 Pa

My inlet and outlet conditions are Velocity Inlet and Flow split outlet, respectively.

I'm sorry but I'm still in the learning stages. Could you please help me out?

vangelis March 26, 2013 07:14

I am not familiar with StarCCM+ unfortunately.
My only guess would be to use another BC type for outlet
like Pressure Outlet instead of Flow Split

I am sure someone more familiar with Star can guide you

good luck

Vangelis

jackwabbit March 26, 2013 08:15

Ah, right. Still, thanks.

rwryne March 27, 2013 15:35

Quote:

Originally Posted by jackwabbit (Post 416437)
I did. But I got a value close to 2 where it was supposed to 1.
My physical conditions with respect to pressure are

Initial conditions
Pressure - 101325 Pa
Reference values
Pressure - 101325 Pa
Force coefficient report
Reference pressure - 101325 Pa

My inlet and outlet conditions are Velocity Inlet and Flow split outlet, respectively.

I'm sorry but I'm still in the learning stages. Could you please help me out?

Just to be clear, you realize that Initial Conditions and Boundary conditions use the reference pressure right? i.e. they are gauge pressures.

So when you set 101325 as your initial condition, you are setting the absolute pressure to 202650. Any pressure other than a "reference pressure" is understood to be <typed in value> + Reference Pressure

jackwabbit March 30, 2013 02:09

Oh, yes. Can't believe I missed that. Thanks! Changed, and it's fine, now.


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