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Research Papers

# Large Eddy Simulation Investigation of Flow and Heat Transfer in a Channel With Dimples and Protrusions

[+] Author and Article Information
Mohammad A. Elyyan, Danesh K. Tafti

High Performance Computational Fluids-Thermal Sciences and Engineering Laboratory, Mechanical Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

J. Turbomach 130(4), 041016 (Aug 04, 2008) (9 pages) doi:10.1115/1.2812412 History: Received June 11, 2007; Revised June 23, 2007; Published August 04, 2008

## Abstract

Large eddy simulation calculations are conducted for flow in a channel with dimples and protrusions on opposite walls with both surfaces heated at three Reynolds numbers, $ReH=220$, 940, and 9300, ranging from laminar, weakly turbulent, to fully turbulent, respectively. Turbulence generated by the separated shear layer in the dimple and along the downstream rim of the dimple is primarily responsible for heat transfer augmentation on the dimple surface. On the other hand, augmentation on the protrusion surface is mostly driven by flow impingement and flow acceleration between protrusions, while the turbulence generated in the wake has a secondary effect. Heat transfer augmentation ratios of 0.99 at $ReH=220,2.9$ at $ReH=940$, and 2.5 at $ReH=9300$ are obtained. Both skin friction and form losses contribute to pressure drop in the channel. Form losses increase from 45% to 80% with increasing Reynolds number. Friction coefficient augmentation ratios of 1.67, 4.82, and 6.37 are obtained at $ReH=220$, 940, and 9300, respectively. Based on the geometry studied, it is found that dimples and protrusions may not be viable heat transfer augmentation surfaces when the flow is steady and laminar.

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## Figures

Figure 1

Geometry specifications

Figure 2

Figure 3

Instantaneous flow velocities

Figure 4

Instantaneous coherent vorticity isosurfaces (level=40) for flow at ReH=9300: (a) at protrusion side; (b) vortex shedding from the back of the protrusion

Figure 5

Instantaneous coherent vorticity isosurfaces (level=40) for flow at ReH=9300: (a) at dimple side; (b) vortex shedding and reattachment at downstream of dimple

Figure 6

Mean 3D velocity streamlines close to the protrusion surface with x-velocity contours very close to channel surface for ReH=220, 940, and 9300

Figure 7

Mean 3D velocity streamlines close to the dimple surface with x-velocity contours very close to channel surface for ReH=220, 940, and 9300

Figure 8

Mean T.K.E. distribution at different spanwise planes across the computational domain for flow at ReH=9300. See text for explanation of labels.

Figure 9

Normalized mean T.K.E. profile at different locations in the domain along the center of the domain, z=0, for ReH=940 and 9300

Figure 10

Mean Nu∕Nu0 distribution on dimple surface for experimental data at ReH=10,400 for channel with aligned dimple and protrusion, Mahmood (9) (reprinted by permission of the American Institute of Aeronautics and Astronautics, Inc.) and current study at ReH=9300. Flow direction is from top to bottom.

Figure 11

Mean Nusselt number augmentation on the protrusion surface for ReH=220, 940, and 9300

Figure 12

Mean Nusselt number augmentation on the dimple surface for ReH=220, 940, and 9300

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