wallGradU components
Hi all
when I use "wallGradU" command for a curved wall (like a cylinder or sphere), i have 3 components for wallGradU in paraview. what are them? are ( dUx/dx , dUy/dy , dUz/dz )? if x, y, z been cartesian system.... or if, for the curved wall, we assume normal spatial component to "n" and tangential components to "t1" and "t2" , then 3 components of wallGradU are (dUn/dn , dUt1/dt1 , dUt2/dt2 ) ??? Thanks all Amin 
Hi Amin,
I think the three components of wallGradU are (Ux/Δ , Uy/Δ , Uz/Δ). where Δ: distance between cell center and the wall U = (Ux, Uy, Uz) The vector wallGradU is the approximation of dU/dn (n: wall normal direction). Hope that helps, Fumiya 
Hello Friends
fumiya, how can you find the location af separation point at a curvactured wall with this component? 
Separation point is where the second derivative becomes zero, there is no way you can find it with first derivative

I have misunderstood the utility "wallGradU" and the "snGrad()" function used in it.
In the utility "wallGradU", the wall normal gradient is calculated using the "snGrad()" function and this function discretizes the normal gradient using the following first order approximation: In fvPatchField.C Code:
00176 // Return gradient at boundary where faceI: label of the face on which we calculate the normal gradient cellI: label of the cell adjacent to the faceI Cf: position vector of face center Cn: position vector of cell center As you can see, the surface normal gradient calculated by wallGradU does not apply any nonorthogonality or skewness corrections. Hope that helps, Fumiya 
thanks all
Mahdi, as i know separation occurs when the first derivation of velocity near the wall becomes zero. Fumiya, is there any way to determine separation point with wallGradU on cylinder? or even with other methods? 
Hi Amin,
I think it depends on your simulations:
In the case of 1 and 2: You can use the wallGradU to find the positions where wall normal gradient of velocity is zero. In the case of 3: You can use the wallShearStress utility to find the positions where the wall shear stress vanishes. Correct the mistakes, if any, in my post. Fumiya 
Quote:
So I believe third method Fumiya mentioned would be the best and most reliable 
Hi Fumiya & Mahdi
Thank you. your comments was so usefull. Regards Amin 
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