Natural Transition in an Adverse Pressure Gradient Boundary Layer

Abstract

The paper is devoted to an experimental study of the natural transition process in boundary layers subjected to an adverse pressure gradient and low free stream turbulence intensity. The study was performed to obtain several goals. The first was to extend the available data-set of transitional boundary layers under adverse pressure gradient with detailed measurements of the streamwise and wall-normal velocity components (mean values and Reynolds stresses), velocity spectra, and measurements of the intermittency across the boundary layer and in the streamwise direction. The velocity spectra were used to verify the applicability of linear stability theory, (especially with respect to the parallel-flow assumption with fast boundary layer growth) and the possible effects of nonlinear interaction (because of the large amplification rates) on transition prediction. The measurements of the intermittency were used to verify available empirical relations, like Klebanoff’s (1956) and Narasimha’s (1957) intermittency distributions, which are often used in models for the flow in the transition region.