I have solved the flow around a 2D cylinder using the IncNavierStokesSolver. Attached, you will find an image of the flow field (flowfield.png). As you can observe, there is a recirculation bubble on the upper rear of the cylinder, along with a separation point at the lower rear.

I am looking to plot the wall shear stress as: sign(wss_x) * wss_mag. I’ve extracted the data using FieldConvert into a .csv file, which is also attached. I have a couple of questions regarding the postprocessing:

1) At the aft (0.5, 0), there’s an abrupt sign change in wss_x, which is not continuous. I believe this is related to how wall normals are defined in Nektar. To correct this, it seems necessary to multiply the wss_x values for the lower surface by -1. I am not sure about the (0.5, 0) itself.
Is there a way to account for this sign change during postprocessing in Nektar? Or would it be possible to apply a preprocessing step in Nekmesh?

2) The simulation was performed with NUMMODES="2" and TYPE="MODIFIED." The edges of each element are duplicated in the .csv file, but the values for these duplicated points are noticeably different (e.g., (-0.4998656761, 0.01158903919) – entries 4 and 5). I suspect this is again related to the normal definitions, as the norm_y values differ significantly. Is there a way to smooth this out, perhaps with a pre- or postprocessing technique?

Also, please note that the region between x = -4.35778714e-02 and 4.35778714e-02 on the upper and lower surfaces does not correspond to the cylinder, which explains the gap in the .csv file.

Thank you in advance for your help. I look forward to your suggestions.