Abstract
The effects of a cavity on hypersonic boundary layer instabilities are investigated experimentally. First- and second-mode wave amplitude evolution is determined using pressure sensors and high-resolution Schlieren technology. The results indicate that when a cavity is located downstream of the fast- and slow-mode synchronization points, it suppresses the second-mode wave and promotes first-mode wave growth. In contrast, when the cavity is located upstream of the synchronization point, the growth of the second-mode wave is promoted while that of the first-mode wave is suppressed. During disturbance evolution, nonlinear interactions are observed due to the phase-locked mechanism that relates the two unstable modes. The transition locations for various cases are confirmed using temperature-sensitive paint technology, and the influences of the cavity on the transition are explained from the perspective of unstable mode amplitude evolution.
Highlights
Turbulent flow is significantly different from laminar flow in terms of surface heating and frictional drag.1–3 boundary-layer transitions are a crucial factor for the design and safe operation of an advanced hypersonic aircraft.Compared to subsonic and moderate-supersonic flows, the transition mechanisms of hypersonic boundary layers are much more complex and much less understood
The results indicate that when a cavity is located downstream of the fast- and slow-mode synchronization points, it suppresses the second-mode wave and promotes first-mode wave growth
The transition locations for various cases are confirmed using temperature-sensitive paint technology, and the influences of the cavity on the transition are explained from the perspective of unstable mode amplitude evolution
Summary
Turbulent flow is significantly different from laminar flow in terms of surface heating and frictional drag. boundary-layer transitions are a crucial factor for the design and safe operation of an advanced hypersonic aircraft. Numerous studies have shown that the effect of the roughness on the second mode wave in the boundary layer is related to the relative position of the synchronization point.. Hao and Wen used direct numerical simulation (DNS) to study the effects of a cavity on hypersonic flat-plate boundary-layer instability. Tian et al. analyzed the effects of ultrasonic absorptive coating (UAC) on both the first and second modes of a 2D high-speed boundary layer using the linear stability theory (LST). They found that Mack mode stability is closely related to the UAC admittance phase, whereas the corresponding stabilization or destabilization effect is intensified by an increase in the admittance magnitude. Position on the transition, one cavity was filled with a rectangular block of the same size as the cavity prior to the flow tests
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