Experimental study of the effect of nose temperature on the disturbance waves in hypersonic boundary layer of blunted cone

The transition of the boundary layer from laminar to turbulent flow significantly impacts the flight stability and safety of aircraft. The aerodynamic heating of the nose of the hypersonic vehicle during flight increases the nose temperature, which affects the stability and transition characteristics of the boundary layer. In this paper, experiments were carried out using a Mach 6, 0° angle of attack conical model to explore the influence of the nose temperature and bluntness on the stability of the conical boundary layer. The wall temperature ratio (the ratio of the nose temperature to the total incoming temperature) T_w/T₀ varies between 0.6 and 1.3, while the nose bluntness R ranges from 0 to 5 mm. Measurements of boundary layer transition and unstable wave were carried out utilizing infrared thermal imaging and high frequency pulsating pressure sensor (PCB). The experimental results show that changing the nose temperature and bluntness affects boundary layer stability. For a sharp cone (R < 50 μm), the nose heating promotes the development of the second mode wave. However, for R = 0.5 mm and 2 mm cones, increasing T_w/T₀ from 0.6 to 1.1 inhibits the development of the second mode wave, while a further increase to 1.3 encourages it. For R = 5 mm cones, nose heating stabilizes the second mode wave.