Investigation of Methods for Re-Establishment of a Laminar Boundary Layer from Turbulent Flow

By means of area suction, laminar flow was reestablished in tripped turbulent boundary layers for a unit Reynolds number range from 0.4 to 1.0 million per foot in incompressible flow. The removal of about 1.5 times the turbulent boundary layer thickness is adequate to restart a maintainable laminar boundary layer. Hot wire observations show that the restarted laminar boundary layer is generally a composite layer with laminar velocity fluctuations from the wall out to about one boundary layer thickness and weak turbulent velocity fluctuations in the outer portion.