LINEAR-STABILITY ANALYSIS IN TRANSONIC DIFFUSER FLOWS

The purpose of this paper is to give the first results of a linear sta bility analysis which has been applied to the problem of shock oscilla tions in a transonic diffuser flow. The mean flow is calculated with a numerical code solving the averaged Navier-Stokes equations, but the proposed stability approach is limited to the core region where the vi scous effects can be neglected. In order to validate the present appro ach, the results are compared with Sajben's experimental results and t hose numerically obtained by Lieu and Coakley. It is the first time th at these published results are compared with a simple linear stability analysis. As demonstrated below, the shock motion spectra have been c orrectly reproduced and the frequencies of 200 Hz and 300 Hz have been clearly obtained for the diffuser lengths of l/h = 13 and l/h = 8.6 r espectively. As far as stability of the mean flow is concerned, the te mporal amplification rate is always negative, the mean flow is therefo re linearly stable. Finally, the amplitude and phase of the fluctuatin g pressure have been compared. The phase for example is in very good a greement with the experimental results. This can prove that at least i n some cases, self-sustained shock oscillations can be explained and p redicted with an inviscid linear stability analysis. (C) Elsevier, Par is.