Effects of ratio of static pressure on velocity characteristics and turbulence intensity of supersonic film cooling over a convex wall

Supersonic film cooling demonstrates superior heat reduction and drag-mitigation effects on a streamwise, convex curved wall. However, it remains essential to clarify how to rationally apply supersonic film cooling on supersonic aircraft. Therefore, schlieren and particle image velocimetry experiments on supersonic film cooling over a convex wall were conducted in a supersonic wind tunnel, combined with Proper Orthogonal Decomposition (POD) to analyze the influence of different ratios of static pressure on the flow. Through velocity profiles and fluctuations, the dynamic evolution process of the favorable pressure gradient effect on the flow over the convex wall was revealed, which can be divided into three stages: incubation stage (x/h ≤ 27), transition stage (27 < x/h ≤ 40), and dominant stage (x/h > 40). POD analysis indicated that within the range of x/h = 33.33–53.33, the cumulative energy contribution of the first 15 POD modes increased with increasing RSP; however, an opposite trend was observed in the range of x/h = 53.33–73.33. Turbulence analysis further identified a significant mechanistic shift during the flow process: within the film exit height (y/h < 1), the film significantly reduced negative Reynolds stress by suppressing the recirculation zone; whereas in the downstream region, as the flow transition completed, turbulent mixing became the dominant mechanism, leading to the reappearance of negative Reynolds stress. This work deepens the understanding of the flow mechanism of supersonic film cooling over a convex wall under varying static pressure ratios, providing a reference for the rational application of supersonic film cooling to achieve efficient heat reduction and drag mitigation during the flight of supersonic aircraft.