Study of shock wave and boundary layer interactions in converging–diverging nozzles with varying inlet air humidity levels

Abstract This paper investigates the interaction between shock waves and boundary layers in half-nozzles under varying nozzle pressure ratios (NPR) and inlet air humidity. Three nozzle geometries (N1, N2, N3) with distinct expansion rates were tested experimentally and numerically under varying nozzle pressure ratios (NPR = 1.4, 1.6, 1.8) and relative humidity levels (30%, 50%, 70%). Experimental methods included high-speed Schlieren imaging (6000 fps) and high-frequency pressure transducers (> 10 kHz), while numerical simulations employed the Unsteady Reynolds-Averaged Navier–Stokes (URANS) method with the k-ω SST turbulence model. Results show that increasing NPR elevates oscillation frequencies, while higher humidity amplifies these frequencies. The URANS method predicted primary frequencies accurately but required hybrid URANS/LES approaches for broader spectral resolution.