Shock boundary-layer interaction on transonic airfoils for laminar and turbulent flow

Abstract

This article deals with the interaction between shocks and the boundary layer in a transonic airfoil flow. Here, examining comparatively the shock boundary-layer interaction in a laminar boundary layer as well as in a fully turbulent one was the main focus of interest. The experimental investigations were carried out in the transonic wind tunnel of the Technical University of Berlin. Apart from conventional time-averaging measuring techniques such as schlieren photography, Laser-2-Focus anemometry, pressure measurement, and visualization, two unsteady measuring techniques were used for investigating the dynamic effects associated with the shock boundary-layer interference. The first unsteady measuring technique concerns a new type of highly sensitive piezoreceivers and in the second technique a piezofoil array was mounted on the airfoil model. The conventional techniques already show decisive differences in the whole flowfield for the cases mentioned. At the same freestream Mach number, the position of the shock is always located further downstream for free transition. These phenomena mainly result from the development of local flow separation regions, which, on their part and with regard to their expansion and structure, strongly depend on the type of the boundary-layer flow. The unsteady measuring techniques were used to detect details in the separation regions and to determine the position of transition in the case of laminar flow. These two phenomena have a decisive influence on the global flowfield as well as on the shock boundary-layer interaction.