Flow transition to turbulence and induced acoustics at Mach 6

Abstract

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, momentumthickness-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 pretty 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.Flow transition to turbulence and induced acoustics at Mach 6

LSTM Reconstruction of Turbulent Pressure Fluctuation Signals

“…The data used in the present study were obtained from the direct numerical simulations (DNS) in [25]. They concern a flow over a flat plate at Mach 6 subjected to von Kármán atmospheric perturbations at the inlet, with a turbulence intensity for the freestream velocity equal to 1%.…”

Wavelet analysis of high-speed transition and turbulence over a flat surface

“…The data used in the present study were obtained from the Direct Numerical Simulations (DNS) of Drikakis et al 13 They concern a hypersonic flow over a flat plate at Mach 6, subjected to von Kármán atmospheric perturbations at the inlet, with a turbulence intensity of the freestream velocity equal to 1%. A detailed description of the method used in the DNS can be found in the study by Kokkinakis et al 22 and the flow parameters in the paper by Drikakis et al 13 . A reference length of x l = 2 mm, calculated as the distance from the leading edge of the plate, has been used to non-dimensionalize the data.…”

“…The DNS aimed to capture the smallest possible tur-bulent scales and their associated acoustic loading near-wall effects. The simulations had captured both transition and fully turbulent flow regions, and further details on the results and flow physics analysis can be found in the reference study of Drikakis et al 13 .…”

“…The random nature of the hypersonic transition process explains its sensitivity to changes in the disturbance environment that can significantly change the transition process 7 . Most of the studies focused on single-mode or 'controlled' transition, but more recent studies considered multimode perturbations, which comprise many waves imitating the von Kármán atmospheric turbulence 8,9,13 .…”

“…This study uses wavelets to analyze recently-published, high-fidelity data from transitional and turbulent BL at Mach 6 13 . We present the coherent and incoherent parts of the flow and enstrophy spectra across the transition and turbulent regions.…”