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Old   March 23, 2013, 02:38
Default Stagnation pressure
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Anonymous 92
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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?
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Old   March 23, 2013, 10:18
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Vangelis Skaperdas
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what value do you get?
higher or lower than expected?

Why the pressure coefficient is greater than one
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Old   March 23, 2013, 13:49
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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.
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Old   March 26, 2013, 03:41
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Vangelis Skaperdas
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Try expressing this value as static pressure coefficient.
This value should equal 1 at stagnation point.
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Old   March 26, 2013, 07:00
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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?
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Old   March 26, 2013, 07:14
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Vangelis Skaperdas
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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
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Old   March 26, 2013, 08:15
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Ah, right. Still, thanks.
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Old   March 27, 2013, 15:35
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Quote:
Originally Posted by jackwabbit View Post
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
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Old   March 30, 2013, 02:09
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Oh, yes. Can't believe I missed that. Thanks! Changed, and it's fine, now.
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