Nusselt Number Behavior on Deep Dimpled Surfaces Within a Channel

Abstract

Experimental results, measured on a dimpled test surface placed on one wall of a channel, are given for a ratio of air inlet stagnation temperature to surface temperature of approximately 0.94, and Reynolds numbers from 12,000 to 70,000. These data include friction factors, local Nusselt numbers, spatially-resolved local Nusselt numbers, and globally-averaged Nusselt numbers. The ratio of dimple depth to dimple print diameter δ/D is 0.3, and the ratio of channel height to dimple print diameter is 1.00. These results are compared to measurements from other investigations with different ratios of dimple depth to dimple print diameter δ/D to provide information on the influences of dimple depth. At all Reynolds numbers considered, local and spatially-resolved Nusselt number augmentations increase as dimple depth increases (and all other experimental and geometric parameters are held approximately constant). These are attributed to: (i) increases in the strengths and intensity of vortices and associated secondary flows ejected from the dimples, as well as (ii) increases in the magnitudes of three-dimensional turbulence production and turbulence transport. The effects of these phenomena are especially apparent in local Nusselt number ratio distributions measured just inside of the dimples, and just downstream of the downstream edges of the dimples.

CFD analysis on the lubrication behaviours of journal bearing with dimples

“…Because the negative valve, in fact, introducing dimple reduces the loading capacity of journal bearing. This is agreement with the conclusion from Ref [4], it may be the negative effect of dimple.…”

“…The lubrication behaviours in the journal/shaft bearing have key influence to its use. In the past, researchers paid more attentions to the study to improve the load capacity of bearing and thermal behaviour by experiment or computational fluid dynamic (CFD) [1] [2][3] [4].…”

“…A number of heat transfer studies from Russia utilize dimple. Heat transfer augmentations as high as 150 percent, compared to smooth surfaces, are reported with appreciable pressure losses [4].…”

Dimples and heat transfer efficiency

“…The minimum heat transfer was observed in the flow-recirculation region inside the dimple. Through experiments, Burgess et al 15 showed the influence of the dimple depth and the dimple imprint diameter on heat transfer, and found that the local and spatially-averaged Nusselt number augmentations increase with an increase in the dimple depth, for various Reynolds numbers from 12,000 to 70,000. Doo et al 16 conducted a parametric study on flows passing through a channel with newly designed surface shapes that comprised of a combination of dimple and riblet.…”

Synergistic integration of computational fluid dynamics and experimental fluid dynamics for ground effect aerodynamics studies

“…Dimples recessed into a flat plane are of interest due to the ability they have in mixing the boundary layer [15][16][17]. Previous numerical work has focused on the dimple flow structure along with some limited flow visualization experiments with which to make com parisons.…”