Sawant, Saurabh S, Theofilis, Vassilios 
ORCID: 0000-0002-7720-3434 and Levin, Deborah A
(2021)
Kinetic modelling of three-dimensional shock/laminar separation bubble
instabilities in hypersonic flows over a double wedge.
[Preprint]
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Abstract
Linear global instability of the three-dimensional (3-D), spanwise-homogeneous laminar separation bubble (LSB) induced by shock-wave/boundary-layer interaction (SBLI) in a Mach 7 flow of nitrogen over a $30^{\circ}-55^{\circ}$ double wedge is studied. At these conditions corresponding to a freestream unit Reynolds number, $Re_1=5.2\times 10^{4}$ m$^{-1}$, the flow exhibits rarefaction effects and comparable shock-thicknesses to the size of the boundary-layer at separation. This, in turn, requires the use of the high-fidelity Direct Simulation Monte Carlo (DSMC) method to accurately resolve unsteady flow features. We show for the first time that the LSB sustains self-excited, small-amplitude, 3-D perturbations that lead to spanwise-periodic flow structures not only in and downstream of the separated region, as seen in a multitude of experiments and numerical simulations, but also in the internal structure of the separation and detached shock layers. The spanwise-periodicity length and growth rate of the structures in the two zones are found to be identical. It is shown that the linear global instability leads to low-frequency unsteadiness of the triple point formed by the intersection of separation and detached shocks, corresponding to a Strouhal number of $St\sim0.02$. Linear superposition of the spanwise-homogeneous base flow and the leading 3-D flow eigenmode provides further evidence of the strong coupling between linear instability in the LSB and the shock layer.
| Item Type: | Preprint |
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| Additional Information: | 32 pages, 13 figures |
| Uncontrolled Keywords: | physics.flu-dyn, physics.flu-dyn |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 01 Feb 2021 07:57 |
| Last Modified: | 15 Mar 2024 11:46 |
| DOI: | 10.48550/arxiv.2101.08957 |
| Related URLs: | |
| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3115029 |
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