Journal
JOURNAL OF FLUID MECHANICS
Volume 935, Issue -, Pages -Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2021.1137
Keywords
high-speed flow; boundary layer separation; hypersonic flow
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Funding
- Hong Kong Research Grants Council [15206519, 25203721]
- National Natural Science Foundation of China [12102377]
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This study investigates the hypersonic laminar flow over a canonical 25 degrees-55 degrees double cone using computational fluid dynamics and global stability analysis. The results show that secondary separation occurs beyond a critical Reynolds number and the flow stability is influenced by multiple factors.
Hypersonic laminar flow over a canonical 25 degrees-55 degrees double cone is studied using computational fluid dynamics and global stability analysis (GSA) with a free-stream Mach number of 11.5 and various unit Reynolds numbers. Axisymmetric simulations reveal that secondary separation occurs beneath the primary separation bubble beyond a critical Reynolds number. The numerical results agree well with existing experiments and the triple-deck theory with the axisymmetric effect on the incoming boundary layer treated by the Mangler transformation. The GSA identifies a three-dimensional global instability that is azimuthally periodic immediately prior to the emergence of secondary separation. The criterion of the onset of global instability in terms of a scaled deflection angle established for supersonic compression corner flows (Hao et al., J. Fluid Mech., vol. 919, 2021, A4) can be directly applied to double-cone flows. As the Reynolds number is further increased, the flow is strongly destabilized with the coexistence of multiple stationary and low-frequency oscillating unstable modes. Direct numerical simulations confirm that the supercritical double-cone flow is intrinsically three-dimensional, unsteady and exhibits strong azimuthal variations in the peak heating.
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