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Direct numerical simulation of grid-element turbulence and its effect on heat transfer

Event Type: 
Date and Time: 
Friday, May 18, 2018 - 16:30
Location: 
CTR Conference Room 103
Event Sponsor: 
Parviz Moin, Director of Center for Turbulence Research
Speaker(s): 
Dr. Immanuvel Paul
Fractal-grid-generated turbulence has gained considerable attention in the past decade owing to its novel unique characteristics including the nonequilibrium energy cascade present in the near field. This talk will present direct numerical simulation results of turbulence generated by a simplified fractal grid called a square grid-element.
                     
This talk consists of three parts. The first part focuses on the small-scale dynamics of grid-element turbulence. Specifically, the generating mechanisms and the dynamics of velocity gradient tensor, in the downstream of the grid-element, are studied. An attempt is made to establish the relationship between the small-scale dynamics and the energy cascade by exploring the vortex stretching term in detail. In the second part, a passive scalar is continually injected into the wakes of the grid-element and the scalar small-scale dynamics are analyzed. A nonzero lateral scalar gradient skewness is observed along the far-downstream homogeneous region despite the absence of mean gradients. Through a conditional statistical analysis, the source and mechanism of scalar anisotropy in heated grid-element turbulence are revealed. In the final part, the effect of grid-element turbulence on heat transfer is studied by placing heated cylinders in the wake of an insulated grid-element. The turbulence in the near-field of the grid-element is found to have some unique characteristics that cause unusual stagnation-point heat transfer increase. The probable reasons for this increase along with heat transfer mechanisms are explored.
 
Bio: 
Dr. Immanuvel Paul obtained his PhD from Imperial College London in May 2017. He has been working on fractal-grid-generated turbulence, fine-scale structure of fluid and scalar turbulence, numerical heat transfer, laminar and turbulent wakes, and immersed boundary methods. He is interested in studying the computational and physical aspects of particle-laden flows with heat transfer.