Delayed transition in a plane channel flow with high contraction ratio

Raghuram, S and Ramesh, ON (2021) Delayed transition in a plane channel flow with high contraction ratio. In: Experiments in Fluids, 62 (7).

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Abstract

Abstract: Large delay in the onset of laminar�turbulent transition and the protraction of its extent in a channel flow are achieved by connecting it to a wind tunnel with very high effective area contraction ratio (c). Fully developed flow is established in the channel using a blower-based open-circuit wind tunnel, and 2D velocity field is measured using particle image velocimetry. The contractions are carefully designed with optimal parameters so as to have minimal non-uniformity at the exit, avoidance of boundary layer separation at the contraction inlet and exit and reduction in turbulence levels in the flow. This ultrahigh contraction ratio causes large reduction in the disturbance levels leading to delay in the onset of transition (at Re m= 2050 rather than the usual value of around 1500) and protraction of the extent of the transitional regime by around 4 times (� Re m= 3150 as opposed to the usual value of around 800). Here Rem=2umhν is the bulk Reynolds number, um is the bulk velocity, h the channel half height and ν the kinematic viscosity. This is confirmed by the values of the centerline turbulence intensity obtained around the onset of transition from current measurements, which are found to be lower than those from other studies in the literature with lower values of c. Graphic abstract: Figure not available: see fulltext. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

Item Type:	Journal Article
Publication:	Experiments in Fluids
Publisher:	Springer Science and Business Media Deutschland GmbH
Additional Information:	The copyright for this article belongs to Springer Science and Business Media Deutschland GmbH
Keywords:	Boundary layers; Channel flow; Reynolds number; Turbulence; Velocity; Velocity measurement; Wind tunnels, Boundary-layer separation; Disturbance level; Fully developed flows; Open circuit wind tunnels; Particle image velocimetries; Transitional regimes; Turbulence intensity; Turbulent transition, Atmospheric thermodynamics
Department/Centre:	Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited:	02 Aug 2021 08:49
Last Modified:	02 Aug 2021 08:49
URI:	http://eprints.iisc.ac.in/id/eprint/69002

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