Experimental study on instability and transition over hypersonic boundary layer on a straight cone

The instability and transition of a cone model with a nose radius of 2 mm and a half cone angle of 7° were studied using infrared thermography and a high-frequency pressure sensor （PCB） at Ma = 6. The experimental results show the presence of a stationary crossflow streaks, low and high frequency unstable waves in the three-dimensional boundary layer of the straight cone in the flow field of a conventional hypersonic wind tunnel. Under nonzero angle of attack, low-frequency （15−50 kHz） and high-frequency （210−340 kHz） unstable waves exist at the same time, and the boundary layer transition is more likely to occur. With the increase of the angle of attack, the streaks become clearer, the transition front of the model moves toward the windward side, and the amplitude of low-frequency and high-frequency unstable waves increases and the band ranges enlarge. The amplitude of the unstable waves increases and the frequency band widens, and the low-frequency unstable waves appear earlier than the high-frequency unstable waves. At the same angle of attack, with the increase of unit Reynolds number, high-frequency and low-frequency unstable waves and stationary crossflow streaks appear earlier and grow to saturation, accompanied by the increase of the amplitude and bandwidth of the unstable waves. In addition, the low frequency unstable waves appear earlier than the high-frequency unstable waves.