Streamwise vortex instability is one of the most potent mechanisms for the transition of the three-dimensional boundary layers.By using the global stability analysis methods,stability characteristics of the leeward vo...Streamwise vortex instability is one of the most potent mechanisms for the transition of the three-dimensional boundary layers.By using the global stability analysis methods,stability characteristics of the leeward vortex over a blunt cone with an angle of attack under a typical wind tunnel condition are studied and are compared to the case with a smaller wall temperature ratio(corresponding to a flight condition).The vortical structure features inward and outward vortices,similar to that in the flight con-dition.Unlike the flight condition,the outward vortices appear stronger than the inward vortices,resulting in stronger outer-mode instabilities.Although the inner mode is heavily stabilized compared to the flight condition,it can still radiate apparent acoustics.The acoustic sources are computed based on Lighthill's acoustic analogy,showing that the entropy term measuring the deviation from the isentropic relation is dominant.While Mack second mode is shown to most likely trigger the transition in the flight condition,it is absent in the wind tunnel condition,and a shear-layer mode turns out to be the most dangerous instead.Moreover,the instability frequencies and growth rates of the wind tunnel case are much smaller than those of the flight case,indicating that wall heating may stabilize the leeward vortices.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.92052301).
文摘Streamwise vortex instability is one of the most potent mechanisms for the transition of the three-dimensional boundary layers.By using the global stability analysis methods,stability characteristics of the leeward vortex over a blunt cone with an angle of attack under a typical wind tunnel condition are studied and are compared to the case with a smaller wall temperature ratio(corresponding to a flight condition).The vortical structure features inward and outward vortices,similar to that in the flight con-dition.Unlike the flight condition,the outward vortices appear stronger than the inward vortices,resulting in stronger outer-mode instabilities.Although the inner mode is heavily stabilized compared to the flight condition,it can still radiate apparent acoustics.The acoustic sources are computed based on Lighthill's acoustic analogy,showing that the entropy term measuring the deviation from the isentropic relation is dominant.While Mack second mode is shown to most likely trigger the transition in the flight condition,it is absent in the wind tunnel condition,and a shear-layer mode turns out to be the most dangerous instead.Moreover,the instability frequencies and growth rates of the wind tunnel case are much smaller than those of the flight case,indicating that wall heating may stabilize the leeward vortices.
