Balakrishna, N and Mathew, J and Samanta, A (2022) ON LATE STAGES OF TRANSITION IN ROUND JETS. In: 12th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2022, 19 - 22 July 2022, Osaka, Virtual.
Full text not available from this repository.Abstract
The bounding shear layer present near the nozzle exit of low-speed round jets undergoes Kelvin-Helmholtz instability that rolls up into vortex rings. These rings experience azimuthal instability and the ensuing nonlinear evolution sees the formation of secondary structures and the ejection of hairpin vortices into the wake of the ring. The importance of hairpin vortices in the laminar-turbulent transition process of round jets has received little attention, and this is a preliminary work in that direction. Using Direct Numerical Simulations (DNS), we study the evolution of an isolated hairpin vortex, modelled as a semi-ellipse with a Gaussian vorticity distribution in its core. The evolution is also explored in the presence of a uniformly convecting stream and a uniformly sheared background flow. The tip of the hairpin vortex moves up due to self-induction, while its legs approach each other upstream of the tip. This leads to a viscous vortex reconnection process leading to the pinch-off of ring-like vortices. Such reconnections of hairpin vortices, considered here, are qualitatively similar to those observed in other configurations, like antiparallel line vortices. As the Reynolds number increases, the time to reconnect decreases, while it occurs for increasingly smaller times. The presence of a uniformly convecting background flow has no effect on the reconnection process, while a uniform shear either accelerates or decelerates the process, depending upon the sense of this shear. This study shows hairpin vortex reconnection to be an important mechanism in the formation of small scales in the wake of vortex rings during a round jet transition. © 2022 12th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2022. All rights reserved.
| Item Type: | Conference Paper |
|---|---|
| Publication: | 12th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2022 |
| Publisher: | International Symposium on Turbulence and Shear Flow Phenomena, TSFP |
| Additional Information: | The copyright for this article belongs to International Symposium on Turbulence and Shear Flow Phenomena, TSFP |
| Keywords: | Reynolds number; Shear flow; Turbulence; Vortex flow, Background flow; Hairpin vortices; Kelvin- helmholtz instabilities; Late stage; Low speed; Nozzle exits; Round jets; Shear layer; Vortex reconnection; Vortex rings, Wakes |
| Department/Centre: | Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering) |
| Date Deposited: | 22 Jan 2023 06:28 |
| Last Modified: | 22 Jan 2023 06:28 |
| URI: | https://eprints.iisc.ac.in/id/eprint/79223 |
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