CFDPost: Calculation of pressure difference between two faces

danishrehman · September 7, 2014, 21:42

Hey helping people, I am in dire need...
I have a body (attached) with small thickness i.e. 5mm. After analysis, I want to see the net pressure (i.e. Upper surface-Lower Surface) but apparently I cant do it anyhow after so much of time spending. Images that are attached are two contours. One for upper surface and one for lower surface, I want to generate a net Pressure contour... Is it possible in post? Since mesh is unstructured, I really cant post process it on my own in MATLAB which in case of structured would have been easier. So suggestions please.

Thanking you in anticipation.

oj.bulmer · September 9, 2014, 10:29

How about calculating the area average pressure on both the surfaces and then subtracting as you want? You have to create an expression for this and then just evaluate it.

Be aware that contours can only be obtained for variables available to CFD-Post at every point. Net pressure as you define will only have one global value, and hence can not be plotted on contour plot.

danishrehman · September 9, 2014, 15:48

Thankyou so much oj.bulmer,

You have provided me a nice path to follow. Following your idea lead me some more questions, so thought to spill them out...

The aim of my study is to perform structural analysis based on wind loads on this structure. I have done all the CFD simulations using non-dimensional model. Now all the net average forces/ net pressure on the surfaces that I would calculate from non dimensional results would not be representative of full scale, therefore I wont be able to apply them. However pressure coefficient is a dimensionless parameter and I was wondering if I define Cp as a variable and then do areaAve(Cp)@'mysurfaces'. Later multiply it with dynamic pressure of full scale values i.e. (0.5*dens*U_ref^2), I should be able to end up with full scale average pressure on the surfaces that I can use to do my structural analysis.

Is it a right approach? Or I should perform one full scale CFD analysis as well and then calculate average net pressures on the surfaces?

Thanks again for the time.

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September 9, 2014, 10:29		#2
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 20	How about calculating the area average pressure on both the surfaces and then subtracting as you want? You have to create an expression for this and then just evaluate it. Be aware that contours can only be obtained for variables available to CFD-Post at every point. Net pressure as you define will only have one global value, and hence can not be plotted on contour plot.

September 9, 2014, 15:48		#3
danishrehman New Member Danish Join Date: Jan 2012 Posts: 4 Rep Power: 14	Thankyou so much oj.bulmer, You have provided me a nice path to follow. Following your idea lead me some more questions, so thought to spill them out... The aim of my study is to perform structural analysis based on wind loads on this structure. I have done all the CFD simulations using non-dimensional model. Now all the net average forces/ net pressure on the surfaces that I would calculate from non dimensional results would not be representative of full scale, therefore I wont be able to apply them. However pressure coefficient is a dimensionless parameter and I was wondering if I define Cp as a variable and then do areaAve(Cp)@'mysurfaces'. Later multiply it with dynamic pressure of full scale values i.e. (0.5densU_ref^2), I should be able to end up with full scale average pressure on the surfaces that I can use to do my structural analysis. Is it a right approach? Or I should perform one full scale CFD analysis as well and then calculate average net pressures on the surfaces? Thanks again for the time.