[cwl6750084]

I am calculating a fluid flow in a CD nozzle. Fluent computes a quantity "wall shear stress", which I assume is the black arrow in the attached figure. How do I compute the normal stress from Fluent? I do not see it anywhere in the dropdown manuals, neither seeing it in the Help/Manual. Does anyone have any ideas on this? I have been struggling with this for a week now.

Thanks for any comments on this.

[vinerm]

Actually, you know it and everybody knows it. The only difference is that the fluids community does not usually use the term normal stress to define it, we prefer to call it pressure.

[cwl6750084]

Thanks for your answer. Just want to make sure, I always thought that pressure is normal to the bulk flow direction, yet the normal stress must be perpendicular normal to the wall surface locally. Are the two the same?

[vinerm]

Pressure is always normal to each boundary. If there is an angle, then it implies shear stress.

[cwl6750084]

Thanks for that. So, if pressure given by Fluent (assuming the one at the node right next to the wall) is the normal stress (the red arrow in the original figure), which angle is the one you mentioned. (Sorry that I am not very good in mechanics.)

[vinerm]

A force vector acting on a solid object can always be resolved into normal and tangential components. It is possible that whole of the vector is normal to the wall or it has an angle other than 90. In the latter case, there will be some shear stress due to the tangential component, while the normal component would be called pressure.