# Comsol-Shear stress with velocity profile

1. Nov 12, 2009

### baranii2000

Dear all,

I was trying to calculate the shear stress due to fluid flow inbetween two parallel plates from the velocity profile taken from the middle of the flow channel (along vertical axis 'y') using comsol. The solution i got is two times the analytical solution i have calculated. The analytical equation i have used here is
Tou=viscosity*(Umax/h)

where tou is shear stress, umax is the max velocity
h is half of the distance between plates.

The calculation with velocity profile from comsol is done by

Tou= viscosity*(du/dy)
du/dy, i calculated with excel from the u,y values in the velocity profile.

the velocity profile is parabolic and looks laminar.
is that i am doing something wrong?

Thanks

Arun

Last edited: Nov 12, 2009
2. Dec 13, 2009

### Brian_C

I think your analytical expression is wrong. For pressure driven flow, there should be a dimensionless parameter which depends on the pressure gradient. Look up Couette flow in any fluid dynamics textbook.