Mechanical and Civil Engineering Seminar: PhD Thesis Defense

Abstract:

Accurate prediction of boundary-layer transition is critical for designing hypersonic thermal protection systems. However, direct numerical simulations (DNS) are impractical for many realistic scenarios, making hypersonic wind tunnel testing essential to the design and further study of such systems. These facilities, though, can face challenges due to significant acoustic noise that primarily originates from the turbulent boundary layers (TBLs) on the tunnel walls.

Motivated by these issues, this thesis investigates acoustic radiation from hypersonic TBLs using resolvent analysis. First, a model capturing the effects of streamwise development on acoustic radiation is developed and employed to study these effects across a range of Mach numbers, Reynolds numbers, and wall-to-recovery temperature ratios. Next, by decomposing the forcing, it is demonstrated that solenoidal forcing is the primary driver of acoustic radiation within the linear formulation. This insight is then applied to estimate freestream statistics using power-spectral density information obtained from a limited number of near-wall measurement planes. Finally, the thesis concludes with an investigation into the optimal linear basis for representing the statistics, with comparisons made to the resolvent basis.