Disturbance Growth in an Unstable Three-Dimensional Boundary Layer

For the study of the transition process in three-dimensional boundary layers, extensive experimental work has been performed by Poll on a yawed circular cylinder [495], Arnal, Coustols and Juillen on a swept wing [496], and Saric and Yeates on a swept flat plate opposite to a bump on the tunnel wall [497]. In these investigations, the governing instability mechanisms have been examined and transition criteria have been established (Arnal, Habiballah and Coustols [498]) or validated and modified (Poll [495]). The theoretical treatment of this problem started by Stuart (in Gregory, Stuart and Walker [499]) is also advanced (e.g. [453, 496, 500, 501]) but its verification still suffers from a deficiency of theoretical and experimental details as well. The present experiment is part of a common theoretical and experimental effort spent for extending the basic description of the transition process in three-dimensional boundary layers. For both the theoretical and experimental work, the accelerated quasi two-dimensional flow past a swept flat plate was chosen in order to simplify the problem as far as possible. The investigations were carried out so far under conditions of natural transition in order to be able to detect the inherent instability features.