In the present paper,extremely unsteady shock wave buffet induced by strong shock wave/boundary-layer interactions (SWBLI) on the upper surface of an OAT15A supercritical airfoil at Mach number of 0.73 and angle of attack of 3.5 degrees is first numerically simulated by IDDES,one of the most advanced RANS/LES hybrid methods.The results imply that conventional URANS methods are unable to effectively predict the buffet phenomenon on the wing surface;IDDES,which involves more flow physics,predicted buffet phenomenon.Some complex flow phenomena are predicted and demonstrated,such as periodical oscillations of shock wave in the streamwise direction,strong shear layer detached from the shock wave due to SWBLI and plenty of small scale structures broken down by the shear layer instability and in the wake.The root mean square (RMS) of fluctuating pressure coefficients and streamwise range of shock wave oscillation reasonably agree with experimental data.Then,two vortex generators (VG) both with an inclination angle of 30 degrees to the main flow directions are mounted in front of the shock wave region on the upper surface to suppress shock wave buffet.The results show that shock wave buffet can be significantly suppressed by VGs,the RMS level of pressure in the buffet region is effectively reduced,and averaged shock wave position is obviously pushed downstream,resulting in increased total lift.
IDDES method was applied to investigate the highly unsteady flow in a subsonic compressor stator with very large hub clearance and high incidence angle.The blade loading variation frequency was found close to the rotating instability(RI)frequency f RI&333 Hz observed in the experiment.Detailed analysis of the flow physics shows that the loading variation is caused by the periodic swing of the large scale separated flow on the blade suction side surface.The breakdown of the leakage vortex has no significant dominant frequencies,thus cannot be the cause of RI in this compressor stator as normally believed.Furthermore,the vortex shedding and vortex breakdown due to shear layer instability at the outer edge of the blade suction surface separation region excite high frequency unsteadiness that can form the sources of noise.
The crossflow instability of a three-dimensional boundary layer is a main factor affecting the transition around the swept-wing.The three-dimensional boundary layer flow affected by the saturated crossflow vortex is very sensitive to the high frequency disturbances,which foreshadows that the swept wing flow transition will happen.The primary instability of the compressible flow over a swept wing is investigated with nonlinear parabolized stability equations (NPSE).The Floquet theory is then applied to the analysis of the influence of localized steady suction on the secondary instability of crossflow vortex.The results show that suction can significantly suppress the growth of the crossflow mode as well as the secondary instability modes.
