A fast and easy-to-use linear stability analyser for wing transition predictions

Abstract

The use of stability analysers based on the linear stability theory and coupled with the en method in flowfield calculation procedures (Viscous/Inviscid Interactive methods, Navier-Stokes solvers) has been impeded by the fact that they require tremendous amounts of information, knowledge and interaction from the user. This paper proposes a systematic procedure in order to obtain a linear stability analyser suitable for integration in wing performance calculation procedures. The emphasis is put on the description of a database for (z) the rapid evaluation of the range in which the critical frequency should lie, (if) the efficient localisation of the points of inception of the instabilities, and, (Hi) to some extent, the crude evaluation of the n-factor growth. Integration of such a procedure into a linear stability analyser will result in improved efficiency and ease of utilisation. This systematic methodology is based on the matching of tabulated stability characteristics of a model (self-similar) boundary layer with the actual three-dimensional (non-similar) boundary layer growing on a wing. It has been found that for near-Blasius strearnwise velocity profiles, the model boundary layer equations chosen admit only a zerocrossflow-velocity solution. A technique to circumvent this difficulty is presented in this paper. The results obtained so far are promising. They show that it is possible to appropriately represent the stability characteristics of the compressible three-dimensional boundary layer of interest by those of a model boundary layer.