Example 4.1. Air at 20C and 0.5105 N/m (0.5 bar) flows over a flat plate with a velocity of 60 m/s. The length of the plate is 25 cm. Calculate the boundary-layer thickness at various locations along the plate. Solution From Appendix B the kinematic viscosity of air at 20 C and atmospheric pressure is vo = 15.11 x 10-6 m/s. Since the variation of the dynamic viscosity with pressure is negligible, the kinematic viscosity of air at 0.5105 N/m and 20 C can be found from the equation of state, i.e., v = Vo Po P = 2vo = 2 x 15.11 x 10-6 m2/s = 30.22 x 10-6 m/s. The thickness of the boundary layer can now be calculated from Eq. (4.34a): (30.22 x 10-6)x 8 = 5.0 = 3.55 x 10-3x m. 60 4.2 Plot the distribution of the velocity u in the boundary layer of Example 4.1 at a distance 15 cm from the leading edge of the plate.