Seminars

Abstract

The effects of Mach number and shock strength on large-scale unsteadiness in shock/boundary-layer interaction (SBLI) were experimentally studied using a compression ramp with varying angles to modify shock strength and mean separation length-scales. Three cases were examined: (1) a 20-degree ramp in Mach 2 flow (weak interaction), (2) a 26.5-degree ramp in Mach 5 flow (weak interaction), and (3) a 28-degree ramp in Mach 5 flow (stronger interaction). Fast-response pressure-sensitive paint (PSP) and time-resolved particle image velocimetry (PIV) captured the surface pressure and velocity fields. PIV was conducted at 50 kHz for Mach 2 and 100 kHz for Mach 5, enabling analysis of turbulent structures in the boundary and shear layers. The PSP enabled spectral analysis of the unsteady pressure field, and revealed the presence of downstream Görtler-like vortices. Results showed two types of shock oscillation: (1) global unsteadiness and (2) local spanwise undulations. Coherence analysis indicated that shock oscillations are primarily linked to downstream flow, while global dynamics are influenced by the incoming flow, which is consistent with the literature. PIV measurements revealed that variations in boundary layer thickness affect separation size, supporting the momentum hypothesis, which suggests that separation bubble size is affected by the boundary layer’s resistance to the adverse pressure gradient. Contrary to the popular view that SBLI dynamics vary with separated flow length scales, the low-frequency unsteadiness mechanism appears to remain consistent across different Mach numbers and ramp conditions.