[Paraview] How does Paraview calculate the velocity gradient

[HongchaoWang]

Hi,

 

How does Paraview calculate the velocity gradient if I use filter "gradient
of unstructured data set"? And what is the difference between using cell
data and point data as input?
 
 
For my case I am simulating an oscillatory flow inside a narrow channel, I
would like to obtain the velocity gradient in order to calculate the shear
stress across the channel. I applied the filter "gradient of unstructured
data set" and use cell data as input. The results are reasonable for most
region in the channel except for the velocity gradient in the first
near-wall cell. The value is about half the analytical solution. Why is
that?
 
 
Many thanks,
Wilson
 
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