Numerical study of heat transfer and flow structure over channel surfaces featuring miniature V rib-dimples with various configurations

Abstract

In order to enhance the heat transfer performance of the internal cooling for gas turbine blades, miniature V rib-dimple hybrid structures on cooling channel surfaces were studied numerically at Re = 50,500, and the effects of parameters of rib heights, dimple depths, rib pitches and rib-to-dimple pitches were detailly investigated on the turbulent flow structure, pressure loss and heat transfer characteristics. The Abe Kondoh Nagano (AKN) k−ε turbulence model was utilized for the numerical simulation work. The results showed that as the rib height and dimple depth increase, the globally averaged heat transfer augmentation increases significantly at first, and then becomes stable. And the maximum heat transfer enhancement is reached when the rib height-to-channel hydraulic diameter ratio is 0.075 and the dimple depth-to-diameter ratio is 0.2. Besides, the more densely fabricated hybrid structures induce higher heat transfer, while a relatively larger spacing between the rib and the downstream dimple also obtains higher heat transfer. Within the parameters of this study, the total heat transfer enhancement of the hybrid structures can be up to 95.3% and 43.2% respectively higher than that of the dimple-only and the rib-only structures. The optimal hybrid structure with the overall thermal performance factor of 1.73, with e/Dh=0.075, δ/d = 0.2, P1/e = 7.2 and L/P1 = 0.83, has a total Nusselt number ratio of 3.9 and a friction ratio of 11.6. It is evident that with the miniature V rib-dimple hybrid structure, the turbulent kinetic energy of the flow passing over the V ribs is enhanced, thereby reducing the recirculation zone in the front of the dimples. Additionally, the vortex flow induced by the V rib strongly interacts with the downstream dimpled wall which significantly augments the overall momentum and heat transport of the near-wall flow field, and contributes to enhanced and more uniformly distributed heat transfer on the channel surface.