Experimental and Theoretical Studies of the Three-Dimensional Boundary-Layer Transition

Abstract

The aim of the investigation, which consists of experiment, theory and numerical simulation, is to better understand, predict and finally control the transition to turbulence in boundary-layer flows. The origins of turbulent flow and the transition to turbulence are dominated by a sequence of instabilities, which leads to a three-dimensional breakdown of the laminar flows. When a laminar boundary layer is three-dimensional in the very first stable regime, it exhibits a transition behavior which is quite different to that of any twodimensional flow. Therefore, - apart from the practical importance in aerodynamics with emphasis on the design of energy-efficient airfoils - an investigation of such inherent three-dimensional phenomena is an extra challenging field in fluid mechanics. Physical modelling of these phenomena requires, in the first stage, the simplification of some three-dimensional complex flow configuration to such a flow that is accessible to direct comparison between experiment, theory and numerical simulation but one which preserves the inherent three-dimensional effects which first appear in swept-wing boundary-layer flows. In the following we summarize such experimental, theoretical and numerical investigations. Details are given in the literature cited.