Influence of Non-Uniform Surface Temperature Distributions on Hypersonic Boundary Layer

Recent Direct Numerical Simulations (DNS) have demonstrated that imposing spanwise non-uniform surface temperature distributions can passively control laminar-to-turbulent transition in hypersonic boundary layers by generating streamwise velocity streaks. This study experimentally investigates the potential of this control mechanism. To inform the experimental design, a combined numerical approach—using three-dimensional DNS and Linear Stability Theory (LST)—was applied to a Mach 5 boundary layer to study the control parameters. Based on these findings, a novel aerodynamic test rig was developed, featuring a specialized sub-surface heating system integrated into a waverider-based model. Guided by transient thermal modeling, the system achieved a spanwise periodic temperature difference of $\Delta T = 85$\,K. Experiments were conducted in the University of Manchester High Supersonic Tunnel at a freestream Mach number of 5 ($Re_\infty=4.8\times10^6$\,m$^{-1}$). Baseline spectral analysis identified a distinct peak centered at 170\,kHz. While uniform wall heating resulted in a general damping of this peak, the non-uniform heating configuration yielded a complex response. Comparison against the baseline revealed distinct spectral modulation, suggesting a modification of the instability mechanism that warrants further detailed characterization. Infrared thermography indicated a maintenance of lower heat flux levels in the downstream region compared to the uniform baseline. These results demonstrate the potential of spanwise surface heating to influence boundary layer stability and suggest a promising pathway for further investigation into spanwise temperature variation control.