# Homework Help: Flow Over Circular Cylinder

1. Oct 11, 2005

### jjiimmyy101

Probably a simple question, but I could use some clarification please.

When we have flow over a simple geometric shape (i.e. a circular cylinder) why does the separation point move further downstream as Reynolds number increases?

Does it have anything to do with pressure difference (I think it does) but what?

2. Jan 31, 2012

### savyasachi

Well, its a good question

We have Reynolds Number, Re = (density x velocity x length)/dynamic viscosty

Seperation occurs due to boundary layer phenomena. and boundary layer is directly proportional to friction (viscosity). i.e., if viscosity rises boundary layer also rises.
lets move to our problem, Increasing Re moves seperation point away from the body.
assume its incomressible flow (density constant), and length remains constant. Now the only variables are velocity and dynamic viscosity. At higher speeds, boundary layer effects are less over the body, since viscocty has no effect on the body at high speeds.

@boundary layer theory by schichting for reference