An airplane flies at a speed of 507 mph at an altitude of 10,000 ft. If the boundary layers on the wing surfaces behave as those on a flat plate,

(a) estimate the extent of laminar boundary layer flow along the wing. Assume a transitional Reynolds number of Rexcr=5 × 105. If the airplane maintains its 539 -mph speed but descends to sea-level elevation,
(b) estimate the extent of the laminar boundary layer flow.
(c) Will the portion of the wing covered by a laminar boundary layer increase or decrease compared with its value at 10,000 ft?

0.17 ft

0.13 ft

Explanation:

a) Obtain the values of density and kinematic viscosity from the table fro the height condition of 10000 ft, and use the transitional Reynolds number (convert the given velocity units, into the units of feet per second) to obtain the x_cr:  

x_cr =   μR_E/ρ*V

       = (2.01*10^-4)*(5*10^5)/587

       = 0.17 ft

b) Obtain the kinematic viscosity at the sea level height, and express the Reynolds number:  

R_E = V*x_cr/v

x_cr = R_E*v/V

       =5*10^5*1.57*10^-4/587

x_cr =0.13 ft

Due to temperature increase with the altitude decrease, the density will also decrease, which is the reason for the obtained difference in the result!  

note:

there maybe error calculation but answer is correct

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