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

  1. Oct 11, 2012 #1
    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
  2. jcsd
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