Experimental Study of Laminar Turbulent Boundary Layer Transition Influenced by Anisotropic Free Stream Turbulence

Abstract

The purpose of this study is to clarify the boundary layer transition process influenced by anisotropic and low-level free stream turbulence generated by a turbulence grid mounted upstream from a contraction. Flow visualization experiments in the boundary layer revealed the appearance of wave packets with streamwise wave numbers that transform into ‘A’ shaped structures and immediately break down into turbulent spots. The wave packets were mapped out around the upper branch of the neutral curve in a linear stability diagram, suggesting the modal disturbance is dominant and triggers transition to turbulence in the boundary layer subject to relatively low-level free stream turbulence on the boundary layer scale.