Unsteady Bounday layer
 

I'm trying to solve a problem where I have impulsively started boundary flow past a circlar cylinder.

If we just consider the top half of the cylinder, then an ideal co-ordinate system is one where the x-coordinate represents the distance along the surface of the cylinder, and the y-coordinate is the distance from the cylinder.

Now, since this flow is unsteady, I expect that the thickness of the boundary layer changes with time. My question is, does the thickness increase or decrease with time?

This is a very new problem to me, but my intuition tells me that the boundary layer gets narrower as the flow progresses.

Is this right?