The stability of compressible swirling pipe flows with density stratification

Yadav, Navneet K and Samanta, Arnab (2017) The stability of compressible swirling pipe flows with density stratification. In: JOURNAL OF FLUID MECHANICS, 823 . pp. 689-715.

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Abstract

We investigate the spatial stability of compressible, viscous pipe flows with radius-dependent mean density profiles, subjected to solid body rotations. For a fixed Rossby number is an element of ( inverse of the rotational speed), as the Reynolds number Re is increased, the flow transitions from being stable to convectively unstable, usually leading to absolute instability. If flow compressibility is unimportant and Re is held constant, there appears to be a maximum Re below which the flow remains stable irrespective of any rotational speed, or a minimum azimuthal Reynolds number Re-theta (= Re/is an element of) is required for any occurrence of absolute instabilities. Once compressible forces are significant, the effect of pressure-density coupling is found to be more severe below a critical Re, where as rotational speeds are raised, a stable flow almost directly transitions to an absolutely unstable state. This happens at a critical Re-theta which reduces with increased flow Mach number, pointing to compressibility aiding in the instability at these lower Reynolds numbers. However, at higher Re, above the critical value, the traditional stabilizing role of compressibility is recovered if mean density stratification exists, where the gradients of density play an equally important role, more so at the higher azimuthal modes. A total disturbance energy-based formulation is used to obtain mechanistic understanding at these stability states, where we find the entropic energy perturbations to dominate as the primary instability mechanism, in sharp contrast to the energy due to axial shear, known to play a leading role in incompressible swirling flows.

Item Type:	Journal Article
Publication:	JOURNAL OF FLUID MECHANICS
Additional Information:	Copy right for this article belongs to the CAMBRIDGE UNIV PRESS, 32 AVENUE OF THE AMERICAS, NEW YORK, NY 10013-2473 USA
Department/Centre:	Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited:	29 Jul 2017 07:37
Last Modified:	29 Jul 2017 07:37
URI:	http://eprints.iisc.ac.in/id/eprint/57511

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