Streamwise evolution of turbulent flow and heat transfer over channel surfaces with V ribs and V-rib-dimple compound turbulators

Scale-Adaptive Simulations (SAS) were carried out to investigate streamwise evolution of turbulent flow and heat transfer over channel surfaces with V ribs and V-rib-dimple compound turbulators. The compound turbulators periodically consist of 45 V-shaped ribs and spherical dimples of varied sizes placed on the channel wall between the V-ribs. Three sets of dimple sizes are investigated with the same depth-printed diameter ratio of hd/d = 0.2. The aspect ratio of the rectangular channel is W/H = 4, and the rib pitch-to-height ratio is P/e = 10. The greatest global heat transfer enhancement and overall thermal performance is achieved by the V-rib-dimple case with the printed dimple diameter-rib pitch ratio of d/P = 0.167. Obvious streamwise development characteristics of the turbulent flow structure and heat transfer enhancement are observed in the V-rib and V-rib-dimple channels, and the key findings are as follows. (1) For the V-rib-dimple cases, the global heat transfer enhancement by the presence of dimples significantly depends on the channel length. In terms of heat transfer, the V-rib dimple cases outperform the V-rib case when L/Dh > 5.1 and gain more improvement at larger L/Dh. (2) There is an obvious streamwise evolution of the heat transfer in the V-rib and V-rib-dimple channels. The regional Nusselt number ratios first increase to reach the peak value, then decrease, and finally settle at the fully developed value. Introducing dimples can expand the range of increasing regional heat transfer by over 45%, yielding up to 23.2% higher regional heat transfer for the V-rib-dimple cases in the fully developed region. (3) The near-wall advective transport dominants the local heat transfer for the V-rib case, but it is gradually attenuated as the boundary layer grows thicker, causing the local heat transfer to decrease downstream of the channel. While for the V-rib-dimple cases, the presence of dimples greatly enhances the near-wall turbulent transport, helping keep the high local heat transfer downstream. (4) The presence of dimples between V-ribs reduces the shear stress magnitude on the sidewall, especially in upstream regions, which can result in the lower total flow friction for short channels.

Automated summary

The study investigates the turbulent flow and heat transfer over channel surfaces with V ribs and V-rib-dimple compound turbulators using Scale-Adaptive Simulations (SAS). The presence of dimples significantly enhances heat transfer and depends on the channel length. The introduction of dimples expands the range of increasing regional heat transfer and reduces shear stress on the sidewall.