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Old   June 30, 2016, 19:25
Default CFX Pressures
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Ferruccio Rossi
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Hi everybody,

I am studying pressure variation over an airfoil traveling at 100 m/s at 5,000 meters altitude. I went through the CFX modelling guide but I still can't understand the CFX pressures in detail. I hope you can answer the following questions:

I set my reference pressure at 54050 Pa, because it is the ambient pressure at 5,000 m altitude.

1. I have an outlet where I can specify either "Static pressure" or "Average Static Pressure". What's the difference between the two?
The outlet is far from the wing, so the pressure should be the same as the ambient pressure. So I set the static pressure at 0, because the reference pressure already accounts for it. Is this right?

2. At the inlet I can specify "Total Pressure" or "Static Pressure". I believe the inlet is like the outlet, because it is far from the body, so its pressure should be the same as the ambient pressure. But if input a static pressure, is this added to the reference pressure? And what happens if I input a total pressue? is it added to the reference pressure?

3. At the opening, I can select either "Opening pressure and Dirn" or "Static pressure and Dirn". What's the difference between the two, and how do they relate to the reference pressure?

4. What about the dynamic pressure created by the flow impacting the airfoil? Is it automatically calculated by CFX?

5. When I visualize the pressure load in CFX post, the dynamic pressure is obviously included, correct?


Thank you for your patience.
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Old   June 30, 2016, 20:52
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Glenn Horrocks
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Quote:
"Static pressure" or "Average Static Pressure"
Static pressure applies the specified pressure at all locations on the boundary. Average static pressure allows the pressure to vary over the boundary, but the average is made to be your specified value.

Q2: Yes, both a static and total pressure are relative to the reference pressure.

Q3: Opening pressure uses total pressure for forward flow and static pressure for reverse flow. Static pressure uses static pressure for both cases.

Q4, 5: Yes
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Old   July 1, 2016, 14:25
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Ferruccio Rossi
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thanks ghorrocks, your answer was very clear. The last thing I would like to know is:

if I set total pressure at the inlet, what does the total pressure accounts for? I guess it is the sum of static pressure and dynamic pressure? Am I correct?
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Old   July 2, 2016, 07:51
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Yes, that is right.

Total pressure inlet means that the static pressure plus the dynamic pressure equals the defined amount. Note that you are not really setting a single flow variable here, it is a mixture of pressure and velocity.
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cfx, pressure bc, pressure boundary, reference pressure, relative pressure

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