Kumar, G and Sasidharan, V and Kumara, AG and Duvvuri, S (2024) A model for frequency scaling of flow oscillations in high-speed double cones. In: Journal of Fluid Mechanics, 988 .
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Abstract
Coherent small-amplitude unsteadiness of the shock wave and the separation region over a canonical double cone flow, termed in literature as oscillation-type unsteadiness, is experimentally studied at Mach 6. The double cone model is defined by three non-dimensional geometric parameters: fore- and aft-cone angles (and), and ratio of the conical slant lengths . Previous studies of oscillations have been qualitative in nature, and mostly restricted to a special case of the cone model with fixed and (referred to as the spike-cylinder model), where becomes the sole governing parameter. In the present effort we investigate the self-sustained flow oscillations in the - parameter space for fixed using high-speed schlieren visualisation. The experiments reveal two distinct subtypes of oscillations, characterised by the motion (or lack thereof) of the separation point on the fore-cone surface. The global time scale associated with flow oscillation is extracted using spectral proper orthogonal decomposition. The non-dimensional frequency (Strouhal number) of oscillation is seen to exhibit distinct scaling for the two oscillation subtypes. The relationship observed between the local flow properties, instability of the shear layer, and geometric constraints on the flow suggests that an aeroacoustic feedback mechanism sustains the oscillations. Based on this understanding, a simple model with no empiricism is developed for the Strouhal number. The model predictions are found to match well with experimental measurements. The model provides helpful physical insight into the nature of the self-sustained flow oscillations over a double cone at high speeds. © The Author(s), 2024. Published by Cambridge University Press.
| Item Type: | Journal Article |
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| Publication: | Journal of Fluid Mechanics |
| Publisher: | Cambridge University Press |
| Additional Information: | The copyright for this article belongs to the authors. |
| Keywords: | Cones; Cylinders (shapes); Oscillating cylinders; Oscillating flow; Shear flow, Double cones; Flow instabilities; Flow oscillations; Frequency-scaling; High Speed; High speed flows; Separation regions; Shear-flow instability; Shock-waves; Small amplitude, Strouhal number, frequency analysis; prediction; shear flow; shock wave |
| Department/Centre: | Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering) |
| Date Deposited: | 15 Sep 2024 05:42 |
| Last Modified: | 15 Sep 2024 05:42 |
| URI: | http://eprints.iisc.ac.in/id/eprint/86080 |
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