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Homework Help: Fluid Mechanics Problem

  1. Jul 5, 2015 #1
    1. The problem statement, all variables and given/known data
    A seaplane flies at 100 mph through air at 45 *F. At what distance from the leading edge of the underside of the fuselage does the boundary layer transition to turbulence?

    2. Relevant equations
    Re = pvL/u
    Re is Reynolds number
    p (rho) is the density
    V is the characteristic velocity
    L is the characteristic length
    u (mu) is the viscosity

    3. The attempt at a solution
    For turbulent flow (as said by my prof and the book), Re > 500000. So to find out when it transitions to turbulence, set Re to 500000 and solve for the characteric length L.

    Solving for L, L = (Re)(u)/(p)(v)

    From the appendix, the viscosity of air at 45*F is u = 3.66 x 10^-7 (lbf) (s) /ft^2 and p =. 00245 slug/ft^3. V is 100 mph which becomes 146.666 ft/s. Plugging these in, and Re = 500000, I get am answer of .511 ft.

    The book, however, says the answer is. 295 ft. Can anyone help me out? I believe the calculation is correct as I ran it several times, but is there something I'm doing wrong or an assumption I'm missing? Thanks
  2. jcsd
  3. Jul 6, 2015 #2
    Please show us the calculation, including the manipulation of the units.

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