how to calculate shear stress in a pump

Mohamed911 · January 8, 2020, 10:34

Hello everyone.

currently I'm simulating a pump design using CFX, I want to calculate shear stress in the fluid while passing through the pumps components.

I extracted the velocities (U,V and W) and used them to calculate shear stress

Tou (shear stress) = neu * (du/dy)

the problem is that I'm not sure if the method I used is correct or not

your suggestions please

best regards

ghorrocks · January 8, 2020, 17:42

This is only correct for Newtonian fluids. Also, CFX can output the velocity gradients directly, you don't need to calculate it. You might also need to consider the shear strain rate variables if that is relevant.

Opaque · January 8, 2020, 22:56

The variable "Wall Shear" is already computed and written to the results file for all the wall boundaries. There is no need to compute it separately, likely to make a mistake.

Mohamed911 · January 9, 2020, 07:02

I don't want to calculate wall shear, since I want to know the influence of SS on fluid's particles. i need SS values along the pump.

Mohamed911 · January 9, 2020, 07:05

Quote:

Originally Posted by ghorrocks

This is only correct for Newtonian fluids. Also, CFX can output the velocity gradients directly, you don't need to calculate it. You might also need to consider the shear strain rate variables if that is relevant.

I performed a simulation, and used streamlines as a reference to draw chart for velocity (U,V,W). the data used in chart was exported in a .csv file that I used later to calculate the SS

January 8, 2020, 10:34	how to calculate shear stress in a pump	#1
Mohamed911 Member Join Date: Dec 2019 Posts: 31 Rep Power: 6	Hello everyone. currently I'm simulating a pump design using CFX, I want to calculate shear stress in the fluid while passing through the pumps components. I extracted the velocities (U,V and W) and used them to calculate shear stress Tou (shear stress) = neu * (du/dy) the problem is that I'm not sure if the method I used is correct or not your suggestions please best regards

January 8, 2020, 17:42		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	This is only correct for Newtonian fluids. Also, CFX can output the velocity gradients directly, you don't need to calculate it. You might also need to consider the shear strain rate variables if that is relevant. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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January 8, 2020, 22:56		#3
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	The variable "Wall Shear" is already computed and written to the results file for all the wall boundaries. There is no need to compute it separately, likely to make a mistake.

January 9, 2020, 07:02		#4
Mohamed911 Member Join Date: Dec 2019 Posts: 31 Rep Power: 6	I don't want to calculate wall shear, since I want to know the influence of SS on fluid's particles. i need SS values along the pump.