• Letter

Predominance of pressure transport in spatial energy budget for a mixing layer approaching absolute instability

A. B. Aadhishwaran and Sourabh S. Diwan
Phys. Rev. Fluids 6, L091901 – Published 13 September 2021

Abstract

In this Letter, we report the outcome of a spatial energy budget performed for the linear convective instability of the plane incompressible mixing layer within the inviscid framework. We find that as the critical condition for the onset of absolute instability is approached, the integrated pressure-transport term becomes increasingly more prominent as compared to the integrated production term, and the former dominates the energy budget completely at the critical condition. This implies that, near the threshold of absolute instability, the growth of disturbances is almost entirely due to the pressure-transport mechanism (rather than the more common production mechanism), which is a striking result. The part of the pressure-transport term that represents the work done by the fluctuating pressure forces is seen to be primarily responsible for the observed shift in the energy balance. The profiles of the energy terms reveal a strong coupling between velocity and pressure fluctuations at large cross-stream distances, and a region of negative production whose magnitude increases with increasing counterflow. These results can help us better understand the physical processes causing absolute instability in a mixing layer. In particular, the streamwise redistribution of disturbance energy by fluctuating pressure, which is “nonlocal” in character for incompressible flows, seems to play a key role in this respect.

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  • Received 16 March 2021
  • Accepted 25 August 2021

DOI:https://doi.org/10.1103/PhysRevFluids.6.L091901

©2021 American Physical Society

Physics Subject Headings (PhySH)

Fluid Dynamics

Authors & Affiliations

A. B. Aadhishwaran* and Sourabh S. Diwan

  • Department of Aerospace Engineering, Indian Institute of Science, Bengaluru 560012, India

  • *Present address: Department of Mathematics, Indian Institute of Technology Madras, Chennai 600036, India.
  • Corresponding author: sdiwan@iisc.ac.in

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Issue

Vol. 6, Iss. 9 — September 2021

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