Characteristics of the laminar boundary layer in the presence of elevated free-stream turbulence

The laminar boundary layer on a plate was studied in a low-speed wind tunnel, varying the flow turbulence from 0.3 to 25%. Quantitative estimates are obtained for the increase in boundary layer thickness and shear stresses at the wall and for the decrease in momentum thickness with increasing turbulence. It is shown that the depth of penetration of pulsations into the boundary layer is independent of turbulence and is defined solely by the Reynolds number. The disturbances observed in the boundary layer were greatest at a turbulence on the order of 4.5%. It is noted that the longitudinal scale of turbulence increases monotonically toward the external side of the boundary layer, while the spectral distribution is characterized by low frequencies (up to 300 Hz).