Find the drag over a flat plate with laminar and turbulent boundary layers

1. Oct 11, 2012

strine07

1. The problem statement, all variables and given/known data
Consider a flat plate moving at V = 105 ft/s in an atmosphere with P = 2100 psf and T =
75F, with a viscosity of vis = 3.7373e-7 slug/ft-s. The plate has a 2 foot chord and a 3.5
foot span.
a. Find the drag on the plate for:
i. A boundary layer that is laminar over the entire plate
ii. A boundary layer that is turbulent over the entire plate
b. How thick is the boundary layer at the trailing edge of the plate for the same two
cases? (laminar over entire plate; turbulent over entire plate).
c. If boundary layer transition occurs at Retr = 420,000, how much of the flow over
the plate is laminar?

2. Relevant equations
shear stress= vis(dV/dy) @ the wall (y=0)
Retr= (rho)(V)(xtr)/vis
Boundary thickness (lam)= (5.2x)/(sqrt(Rex))
Boundary thickness (turb)= (.37x)/(Rex^0.2)
3. The attempt at a solution
I'm mostly having trouble with finding the drag on the plate I know it's two times the shear stress (for both sides of the plate) but don't know how to find dV/dy