Atmospheric air at 60°F flows over a flat plate at 300 ft/sec. At x = 20 ft, estimate:

(a) The local skin friction coefficient

(b) The wall shear

(c) The viscous wall-layer thickness

(d) The boundary-layer thickness

Question

Atmospheric air at 60°F flows over a flat plate at 300 ft/sec. At x = 20 ft, estimate:

(a) The local skin friction coefficient

(b) The wall shear

(c) The viscous wall-layer thickness

(d) The boundary-layer thickness

Accepted Answer

a) Use Eq. 8.6.40: [latex]c_{f}=\frac{0.455}{\left[\ln \left(0.06 \frac{300 imes 20}{1.58 imes 10^{-4}} ight) ight]^{2}}=\underline{0.00212}[/latex].

[latex]c_{f}=\frac{0.455}{\left(\ln 0.06 Re _{x} ight)^{2}}[/latex] (8.6.40)

b) [latex] au_{0}=\frac{1}{2} ho U_{\infty}^{2} c_{f}=\frac{1}{2} imes 0.0024 imes 300^{2} imes 0.00212=\underline{0.229 psf }[/latex].

[latex]u_{ au}=\sqrt{\frac{0.229}{0.0024}}=9.77 fps[/latex].

c) [latex]\delta_{v}=\frac{5 v}{u_{ au}}=\frac{5 imes 1.58 imes 10^{-4}}{9.77}=\underline{8.09 imes 10^{-5} ft }[/latex].

d) [latex]\frac{300}{9.77}=2.44 \ln \frac{9.77 \delta}{1.58 imes 10^{-4}}+7.4 . \quad herefore \underline{\delta=0.228 ft }[/latex].

Question 8.124: Atmospheric air at 60°F flows over a flat plate at 300 ft/se...