2021/12/19 by Hemanth Goparaju, Goparaju, Hemanth, Datta V. Gaitonde +1
Earth and Planetary Sciences · Engineering · #Aerodynamics and Acoustics in Jet Flows #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Fluid Dynamics and Turbulent Flows #Meteorological Phenomena and Simulations
paper · pdf · doi:10.48550/arxiv.2112.10049
openalex publication_date 2021/12/19 · openalex created_date 2022/05/05 · openalex updated_date 2026/07/28
The effects of entropic-instabilities on the laminar-turbulent transition dynamics of a blunted flat plate at Mach~4 are numerically investigated through linear and nonlinear approaches. Linear wavepacket analysis reveals amplifying oblique first-modes as well as planar and oblique entropy-layer disturbances. The receptivity of entropic-instabilities is found to be largest for actuation seeded in the entropy-layer; the corresponding linear evolution is characterized by an intensification in the wall-normal plane, coupled with streamwise tilting. The transition process that arises from entropy-layer wave interactions via the oblique breakdown mechanism is examined in detail. Oblique entropy-layer disturbances interact non-linearly with each other and induce streamwise streaks in the boundary-layer. These undergo further destabilization downstream, through a combination of lift-up and Orr-like mechanisms, leading to turbulence onset. Sinuous subharmonic oscillations induced by the entropic-disturbances are the dominant streak instabilities. Slanted hook-shaped structures are observed in the temperature perturbations, and are attributed to an Orr-like mechanism in the entropy-layer. Further, temperature perturbations amplify on the crests of the low-speed streaks in the entropy-layer and generate disturbances through triadic interactions. These disturbances aid in the transfer of perturbation energy into the boundary-layer, eventually leading to spanwise homogenization and near-wall streak generation. Towards the end of the breakdown region, spectral broadening accompanied by the appearance of an inertial sub-range in the boundary-layer indicates the approach of the flow towards turbulence.