Prediction de la transition sur des configurations tridimensionnelles en regime transsonique (French and English text)

The first objective of this thesis is to propose a tool for the prediction of the laminar-turbulent that will be reliable, efficient and easy to use in aerospace industry applications. Together with this objective, a study will also be conducted of how the stability of transonic flows is affected by the following physical aspects: full account of the three-dimensional nature of the mean flow, curvature of the surface along which the flow develops and non-parallel effects.; The proposed transition prediction method relies on the use of a database of stability characteristics of a model three-dimensional compressible boundary layer. A coupling method based on the physical parameters of the mean flow, such as local Mach number, Reynolds number and boundary layer shape factor, allows the extraction from the database of quantities such as the amplification rate for a given frequency or the maximum amplification frequency of the boundary layer studied. The stability characteristics of the model boundary are precomputed, using the compressible linear stability equations with the classical parallel flow assumption and without curvature effects.; Comparing the stability characteristics and n factors obtained from a mean flow calculated by a fully-three-dimensional approach with those that result from the use of a quasi-three-dimensional mean flow (conical flow assumption) shows the significative influence of transverse (or spanwise) pressure gradients on the stability of a three-dimensional flow. In the same way, the potentially strong influence of curvature and non-parallel effects (the latter calculated using the PSE approach), respectively stabilising and destabilising, on the amplification rate of streamwise instabilities was demonstrated. However, the inclusion of these effects does not lead to a more consistent value of the n factor at transition than is obtained by the classical theory, as demonstrated by correlating the calculated values of n with the location of transition determined in windtunnel tests on infinite swept wings with ONERA D and AFVD 82 profiles and Bombardier business aircraft wings.; The results obtained with the proposed automated stability analysis method have shown that it provides a qualitatively adequate representation of a transonic three-dimensional flow stability characteristics: dominant instability type, frequency of maximum amplification, amplification rate. Computation of the n factor was performed for the AS409 conical wing and two Bombardier business aircraft wings. For these cases, the automated method n factors are higher than those obtained by a complete eigenvalue calculation. This difference is probably largely due to the fact the model boundary layer used does not provide a completely appropriate representation of the crossflow velocity profiles. It is however within the range of variation of the n factor from one case to the other, when the full eigenvalue solution is used. Comparison of the calculated n factors and the experimentally observed location of transition on the Bombardier wings has revealed a spanwise variation of the critical n factor, with both the complete and automated calculation methods. To improve the prediction of transition, a relation between the n factor at transition and a local Reynolds number (varying along the span) is proposed.