fluid dynamics - Is it possible to accelerate air to supersonic speeds? What would it look like?

The speed of sound is the rate that disturbances in air propagate through it.

Is it possible to have a wind that itself is moving at supersonic speeds relative to stationary winds around it?

Or perhaps a fluid flowing through a pipe at a speed greater than the speed of sound within it.

If so, what would it "look" like? What kind of phenomenon would occur?