364924 Turbulence in a Microchannel

Wednesday, November 19, 2014: 2:15 PM
M304 (Marriott Marquis Atlanta)
V. Kumaran, Department of Chemical Engineering, Indian Institute of Science, Bangalore, India

Experimental results are presented to show that the laminar-turbulent transition in a microchannel (of height about 100 microns) with a soft wall takes place at a Reynolds number about five times lower than that in a rigid microchannel. The transition mechanism is a dynamical instability due to the fluid-wall coupling, resulting in the spontaneous generation of velocity fluctuations in the fluid and oscillations of the soft wall. The destabilising mechanism is the transfer of energy from the mean flow to the fluctuations due to the shear work done at the interface. The velocity statistics in the turbulent flow are determined using time-resolved Particle Image Velocimetry measurements of the mean velocity and velocity fluctuations. The experiments show that the fluctuating velocity at the soft surface is non-zero, and the streamwise fluctuating velocity is much larger than the cross-stream fluctuating velocity, indicating that the wall fluctuations are primarily tangential to the interface. There is significant turbulent energy production at teh soft surface itself, in contrast to the flow past a rigid surface where the turbulent energy production takes place within the fluid. The efficiency of mixing is measured using a conductivity probe method, and it is found that the mixing time in the turbulent flow is five orders of magnitude lower than the diffusive mixing in a laminar flow.

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See more of this Session: Turbulent and Reactive Flows
See more of this Group/Topical: Engineering Sciences and Fundamentals