Basic experiments on transition in three-dimensional boundary layers dominated by crossflow instability

Abstract

The objective of this review is to summarize the results of basic experiments on the transition process in three-dimensional boundary layers governed by crossflow instability and to inform on the present state of knowledge. In particular, the intent is to give a detailed description of the essential physical features rather than a complete survey on all the experiments known so far. For convenience, emphasis is placed on the experiments carried out at DLR in Göttingen, however, essential contributions of other experiments which complete the physical understanding of the problem or lead to different conclusions are also discussed. The DLR experiments were specifically designed to study the transition process dominated by crossflow instability and to create the database for theoretical and numerical analyses of the disturbance development up to the final breakdown of laminar flow and for transition prediction. These analyses should take into account the physics of transition in a more comprehensive manner than the e N-method allows. It will be shown why, in contrast to transition dominated by Tollmien–Schlichting instability, details of the upstream conditions and the related nonlinear development cannot be ignored. The possibilities for their inclusion are discussed. In this regard, it is of special interest to verify that modern stability analyses enable the quantitative description of the linear and nonlinear disturbance development. High emphasis is placed on comparisons between experiment and nonlinear PSE and DNS approaches.