# Radial and tangential velocities for Inviscid flow (fluid mechanics)

After I have an expression for the stream-function in a problem, I can differentiate to get the tangential and radial velocities because I need those to solve the problem. But I don't understand when the tangential velocity will be 0 and when the radial is 0. Can some on explain?

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Chestermiller
Mentor
After I have an expression for the stream-function in a problem, I can differentiate to get the tangential and radial velocities because I need those to solve the problem. But I don't understand when the tangential velocity will be 0 and when the radial is 0. Can some on explain?
Is this for flow past a cylinder or past a sphere?

Chet

I didn't realize there was a difference but cylinders for this question.

Chestermiller
Mentor
If you're referring to the radial and tangential velocity components at the surface of the cylinder, then the radial component has to be zero, since you can't have flow through the solid surface of the cylinder. For inviscid flow, the tangential component of the velocity does not have to be zero at a solid surface. The leading edge and the trailing edge of the cylinder are both stagnation points, so both components of velocity are zero at these points.

Chet

Thanks for clearing this up.