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In fluid statics pressure always acts normal to the wall . The explanation I have seen

https://www.physicsforums.com/threads/fluid-mechanics-and-perpendicular-force.733437/

Is that while a momentum change with the wall of a container/surface has both a tangential and perpendicular components, as a static fluid has completely random motion over many interactions the tangential components of the forces statistically cancel out leaving only the perpendicular components as a net force

In fluid dynamics under a curved flow the change of the organised momentum/ velocity vector of a fluid results in an inwards force radially towards the centre - Centripetal Force

I could be wrong but to me this appears that this force is again purely perpendicular to the surface but under very different conditions - Under fluid dynamics the tangential components are no longer statistically equal so the net forces do not cancel out but yet we are left with the same perpendicular force situation.

As a further example - if we were to reverse the direction flow (at same velocity/ mass flo rate ) we would still experience the same centripetal force in the same radial direction. It appears the original direction of the momentum is irrelevant to the action of this force.

Could someone please explain how this could be ?