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Old   May 5, 2010, 10:02
Default drag calculation help
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Hi, I have some code where I calculate the drag on an obstacle. In the code I calculate both the pressure drag and the viscous drag on a 2D structure mesh. I'm not certain I do this correct. Could someone confirm that this is correct?

I calculate the pressure drag by integrating the pressure over the left and right surfaces of the obstacle, for example

for(all nodes with right face exposed)
pressureDrag -= dy * pressure_to_right_of_node

for(all nodes with left face exposed)
pressureDrag += dy * pressure_to_left_of_node

The viscous drag is calculated by summing the force due to viscous effects over the top and bottom surfaces of the obstacle.

for(all nodes with top face exposed) {
float shearStress = mu * u[ijp1] / dy;
viscousDrag -= dx * ShearStress;
for(all nodes with bottom face exposed) {
float shearStress = mu * u[ijm1] / dy;
viscousDrag -= dx * ShearStress;

So basically for both types of drag I sum something over all the nodes directly outside the surface of the obstacle. Is this correct?

Thanks in advance for any help, it would be greatly appreciated.
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Old   May 9, 2010, 23:00
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any ideas? thank you
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