Effect of multi-hole film interactions on thermal protection and drag reduction performances under supersonic condition

Hydrocarbon-fueled scramjet engines face significant challenges related to aerodynamic frictional drag and thermal protection due to high-speed incoming flow and high-intensity combustion heat release. Multi-hole discrete film injection using gaseous hydrocarbon fuel can effectively reduce frictional drag while enhancing film cooling performance. Numerical simulations based on the Reynolds-Averaged Navier-Stokes method have been conducted to investigate the effect of multi-hole film interactions on thermal protection and drag reduction performances under supersonic condition in a supersonic combustor. The results indicate that multi-hole discrete film jets achieve better cooling efficiency and broader cooling coverage under supersonic incoming flow conditions compared with subsonic incoming flow at the same blowing ratio. Under subsonic condition, the small velocity difference between the multi-hole discrete film jets and the main flow exacerbates the penetration of the transverse jet into the main flow, leading to a decrease in cooling efficiency. Smaller lateral hole spacing (P/D) is better for combustion drag reduction and thermal protection performances under supersonic conditions, as it enables neighboring jets to form anti-kidney-type vortex pair structures and creates a cracking heat absorption region. Furthermore, the axial hole spacing (S/D) in aligned multi-hole discrete film jets significantly enhances thermal protection performance by regulating the chemical reaction of hydrocarbon fuel and extending the cracking reaction region. Secondary hydrocarbon-fueled film injection extends the cracking reaction region and delays the onset of the combustion heat release zone, thereby expanding the effective cooling region. Moreover, an optimization analysis of the cross multi-hole discrete film jet structure shows that cooling coverage increases to 73.5 % at S/D = 10 and P/D = 2, while the hydrocarbon fuel combustion resistance is reduced by 33.2 %.