Flow transition to turbulence and induced acoustics at Mach 6

Drikakis, Dimitris and Ritos, Konstantinos and Spottswood, S. Michael and Riley, Zachary B. (2021) Flow transition to turbulence and induced acoustics at Mach 6. Physics of Fluids, 33 (7). 076112. ISSN 1070-6631 (https://doi.org/10.1063/5.0054345)

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This paper presents the results of implicit large eddy simulation (iLES) and direct numerical simulation (DNS) for flow and acoustics for transitional and turbulent boundary layer over a flat plate at Mach 6. The DNS was about 50 times more refined grid-wise than iLES. Both DNS and iLES were performed using the same numerical schemes, initial and boundary conditions. We compare the different numerical approaches concerning the shape factor, momentum-thickness-based Reynolds number, heat flux on the wall, Reynolds stress, and near-wall acoustics. We perform pressure fluctuations spectral analysis and propose a predictive model. We show that iLES captures rather accurately the flow and acoustic characteristics in the turbulent region. Differences up to 5 dB occur between iLES and DNS in the transition region. iLES also shifts slightly further downstream the end of the transition and underpredicts the shear stress value peak. The iLES captures the near-wall acoustic spectrum roll-off accurately at low and medium frequencies. It underpredicts high frequencies' content due to grid constraints. Overall, iLES gives excellent results compared to the significantly more refined DNS. The results show that high-order numerical simulations can help adapt and validate semi-empirical models for the engineering design and acoustic loading on hypersonic structures.