# Homework Help: Fluid Dynamics

1. May 16, 2007

### CanoIsDbo

I am having a huge problem with understanding the derivation of velocity profiles for these type of problems. The one i am having the most difficulty is the flow of oil going down vertically along the surface of a glass rod. Where p=900 kg/m^3 and u=120 mPa's. How do I start this problem?

Last edited: May 16, 2007
2. May 20, 2007

### fluidman

here is the key

Start by writing Navier-stokes equations in cylindrical coordinates.And make reasonable assumptions to simplify the equations. Like, 1 The flow is steady and two dimensional in r-z plane. Here z is the coordinate pointing downwards.You can also chose it to be pointing upwards. In both cases you should pay attention to the signs in the equations. 2 The flow is driven by gravational forces. 3 The shear forces on interface of oil and air are negligible. 4 The flow is in only z direction. Thus the r and θ velocities component go to zero.
Now you need to do some integrations. Im leaving the rest to you...
Good luck!