# Homework Help: Fluid Mechanic Integration

1. Jul 19, 2010

### chronicals

1. The problem statement, all variables and given/known data
For turbulent flow in a smooth, circular tube with a radius R, the velocity profile varies according to the following expression at a Reynolds number of about 10^5.

Vx= Vxmax * [(R-r)/R)]^(1/7)

where r is the radial distance from the center and Vmax the maximum velocity at the center. Derive equation relating the average velocity ( bulk velocity ) Vav to Vmax for an incompressible fluid.
( Hint: The integration can be simplified by substitution z for R-r )

2. Relevant equations

3. The attempt at a solution
i don't know which equation i should integrate and how?

2. Jul 19, 2010

### hikaru1221

I guess the average speed is defined as $$<v>=\frac{Q}{A}$$ where Q is the volume of fluid passing through the cross section of area A in 1 second. How do you find Q?

3. Jul 19, 2010

### chronicals

i think working with volume rate is useless

4. Jul 19, 2010

### hikaru1221

Okay, why and what do you think of the solution?