Circular isolators demonstrate a promising prospect due to their superior performance compared to traditional rectangular isolators for a scramjet. In this study, we conduct high-resolution implicit large-eddy simulations of the flow in a backpressured circular duct at two typical inflow Mach numbers of 2.00 and 2.45. For this distinct shock train system, the leading shocks are shaped like hourglasses composed of nearly axisymmetric bifurcated normal shocks; the following shocks are significantly twisted, distorted, and observed to exhibit unsteady large-scale motions at the tail part of the shock train region. Through the azimuthal discrete Fourier transform and proper orthogonal decomposition, these large-scale motions are shown to be closely linked with the coherent helical structures, which are present in two typical forms: the canonical-form ones concentrated in the bulk flow and the two-layer ones occurring in both the bulk and near-wall flow. Moreover, quantitative analysis of correlation functions and power spectral density of wall pressure fluctuations show that the two-layer helical structures greatly contribute to the peaks of wall pressure fluctuation coefficients near the tails of shock trains.
Coherent Helical Structures Inherent to Unsteady Shock Trains in Circular Duct
AIAA Journal ; 1-14
2025-03-01
Article (Journal)
Electronic Resource
English
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