ON THE PRACTICAL APPLICATION OF THE PSE APPROACH TO LINEAR-STABILITY ANALYSIS

The transition to turbulence of the laminar boundary layer plays an im portant role in airfoil design. The new PSE approach is more accurate and consistent than the classical Orr-Sommerfeld theory. The aim of th is paper is to prove that this approach can be routinely used in pract ical applications to study instabilities and to predict the onset of l aminar-turbulent transition. The main difficulty in its intensive use concerns the initialisation. However, systematic studies can be conduc ted and the results presented show that the non-parallel effects are n egligible for streamwise instabilities and strengthen n factor values for crossflow instabilities. In some intermediate cases, the PSE resul ts exhibit large crossflow amplification for low frequencies as well a s large streamwise amplification at higher frequencies, whereas only t he latter one is dominant according to the Orr-Sommerfeld theory. In t hese particular cases, the fluctuation spectra present two relative ma xima (with the PSE) and the instability type and the most amplified fr equencies can therefore be very different from those predicted by the Orr-Sommerfeld theory. (C) Elsevier, Paris.