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Sign Convention of the Total Pressure

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Old   June 6, 2006, 09:35
Default Sign Convention of the Total Pressure
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Cuong Nguyen
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I have a model of fluid flowing through a square cylinder. My interest is total pressure on the surfaces of the cylinder but I am confussing about the sign convention of the pressure.

If anyone knows the sign convention of the total pressure in CFX, please give me some advices.

Thank you very much for your help!

NKC
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Old   June 6, 2006, 09:46
Default Re: Sign Convention of the Total Pressure
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Robin
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The pressure is relative to the Reference Pressure you specified in your Domain.
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Old   June 6, 2006, 20:35
Default Re: Sign Convention of the Total Pressure
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Cuong Nguyen
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Hi Robin,

Value of the pressure is ralatived to the Reference Pressure as you mentioned. But my question is about the direction of the pressure (we may get positive or negative value of pressure at a point on the surface of model), I am wondering that if the pressure is positive then the direction is going inward or outward of the surface or is there any other convention for that.

Can you give me any suggestion for that?

Thank you very much!

NKC

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Old   June 7, 2006, 16:31
Default Re: Sign Convention of the Total Pressure
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Robin
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Hi Cuong,

There is no such thing as negative pressure, even on your surface. Pressure is always positive. The force due to pressure may be negative in a particular direction, however. Force due to pressure is always normal to the surface, but there may be a tangential component due to viscous stresses.

Regards, Robin
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