Transitions in a soft-walled channel

Kumaran, V and Srinivas, SS (2017) Transitions in a soft-walled channel. In: 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017, 6 - 9 July 2017, chicago.

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Abstract

In a soft-walled channel, there is a dynamical instability due to the coupling between the fluid flow and the wall dynamics which leads to a transion to turbulence. The transition Reynolds number is lower than Re=1000 for a rigid channel if the wall elasticity is sufficiently small. The transition Reynolds number depends on the parameter where and are the fluid density and viscosity, G is the shear modulus of the wall material and h is the channel height. The characteristics of the flow after transition are studied using Particle Image Velocimetry (PIV) in a rectangular channel with walls made of polyacrylamide gel, in which one wall is fixed to a rigid substrate and the other wall is unconstrained. The channels have width about 1.3 cm, height (smallest dimension) about 0.6 mm and the length of the channel is about 14 cm. The channels are fabricated with soft polyacrylamide gel with shear modulus about 0.75 kPa. There is a soft-wall transition at a Reynolds number below 1200, where the flow is symmetric about the centerline, and the wall fluctuations are primarily tangential to the surface, and the velocity statistics are independent of downstream distance. As the Reynolds number is increased, there is a second wall-flutter transition at the top unrestrained surface alone, where the profiles of the mean and root-mean-square velocities are larger near the top surface. Downstream traveling waves, which decrease in amplitude, are observed at the top surface with fluctuations both normal and tangential to the surface. The von Karman plots of the near-wall velocity profiles indicate that there is no discernible viscous sub-layer for (yv∗) as low as 2, where y is the distance from the wall, v∗ is the friction velocity and is the kinematic viscosity. There is clear evidence of a logarithmic layer for soft-wall turbulence, but the von Karman constants are very different from those for the flow in a hard-walled channel. However, there is no evidence of a logarithmic layer after the wall-flutter transition as the Reynolds number is further increased.

Item Type:	Conference Paper
Publication:	10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017
Publisher:	International Symposium on Turbulence and Shear Flow Phenomena, TSFP10
Additional Information:	The copyright for this article belongs to International Symposium on Turbulence and Shear Flow Phenomena, TSFP10.
Keywords:	Channel flow; Elastic moduli; Flow of fluids; Flutter (aerodynamics); Reynolds number; Shear strain; Turbulence; Velocity; Velocity measurement; Viscosity, Downstream distances; Dynamical instabilities; Near-wall velocity profile; Particle image velocimetries; Rectangular channel; Root mean square velocity; Transition Reynolds number; Von Karman constant, Shear flow
Department/Centre:	Division of Mechanical Sciences > Chemical Engineering
Date Deposited:	22 Jul 2022 11:28
Last Modified:	22 Jul 2022 11:28
URI:	https://eprints.iisc.ac.in/id/eprint/74731

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