Computations of Flow and Heat Transfer in a Channel With Rows of Hemispherical Cavities

Abstract

Computations were performed to investigate the three-dimensional flow and heat transfer in a high aspect ratio channel in which one or two wall are lined with four rows of hemispherical cavities arranged in a staggered fashion with two Reynolds numbers (23,000 and 46,000). The focus is on understanding the flow induced by cavities and how that flow affects surface heat transfer. Computed results were compared with available experimental data.This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible NavierStokes), and energy closed by the low Reynolds number shear-stress transport k-oi turbulence model (wall functions were not used). Solutions were generated by a cell-centered finite-volume method that uses third-order accurate flux-difference splitting of Roe with limiters, multigrid acceleration of a diagonalized ADI scheme with local time stepping, and patched/overlapped structured grids.

Comparisons of flow structure above dimpled surfaces with different dimple depths in a channel

“…12 A computational simulation of flows over dimpled surfaces in a channel gives flow structures, flow streamlines, temperature distributions, and resulting surface heat transfer distributions for similar geometries and flow conditions. 13 Moon et al 14 give data that show that improvements in heat transfer intensification and pressure losses remain at approximately constant levels for different Reynolds numbers and channel heights. Mahmood et al 1 describe the mechanisms responsible for local and spatially-averaged heat transfer augmentations on flat channel surfaces with an array of dimples on one wall for one channel height equal to 50% of the dimple print diameter.…”

Ultra High Work, High Efficiency Turbines For UAVs

“…More recently heat transfer, and pressure drop measurements, and flow visualization 21,22,49 have been used to explore and document the physical flow mechanisms which result from flow over and in dimples. Flow visualization from Mahmood et al, 21 shows a system of three longitudinal vortex pairs being shed from a round dimple cavity in an array (channel Re =1250 and channel height to dimple depth 0.5), Figure 10.…”

Numerical predictions of augmented heat transfer of an internal blade tip-wall by hemispherical dimples

“…Lagrani et al [16] compared several types of heat transfer augmentation techniques and concluded that dimples exhibit better overall performance than pin-fins, rib turbulators and other surface roughnesses. During recent years, various dimples have received much attention for enhancing heat transfer in internal cooling passages of turbomachineries [17][18][19][20][21][22][23][24][25][26][27]. For example, Chyu et al [17] experimentally studied the heat transfer on staggered dimpled surfaces using the transient liquid crystal method.…”

“…They found that the rotation could augment the heat transfer on dimpled surfaces, especially on the trailing dimpled surface towards which the colder fluid core migrates due to the Coriolis forces. Besides the experimental measurements, numerical simulations are effective means to investigate the details of fluid flow and heat transfer characteristics resulting from dimpled surfaces [23][24][25][26][27]. For examples, Isave et al [24] conducted simulations of the flow structure on a single spherical dimple using a factorized finite-volume method.…”