Computational investigation of dimple effects on heat transfer and friction factor in a lamilloy cooling structure

Good heat transfer performance with a moderate pressure drop penalty contributes to the gas turbine engine lifetime and guaranteeing engine efficiency. In this study, the dimple effects for a Lamilloy^® (Allison Advanced Development Corporation, Indiana, IN, USA) cooling structure on the heat transfer and friction factor are numerically investigated. The dimple is positioned directly under the jet impingement nozzle. The Reynolds number ranges from 10,000 to 70,000, the dimple normalized depth is between 0 and 0.3, and the dimple normalized diameter varies from 1 to 2.5. The results for the flow field, target surface heat transfer, pin fin surface heat transfer, friction factor, and solid domain outer-wall temperature are included. For comparison, a Lamilloy cooling structure without the dimple is considered as the baseline. The results show that the dimple significantly increases the local heat transfer due to flow reattachment and recirculation. With an increase in the normalized dimple depth, the heat transfer on the target surface is first augmented due to the increase of flow reattachment and recirculation, and then it is decreased due to the large toroidal vortex. However, an increase in the dimple depth results in reduction of the pin fin surface heat transfer. As the dimple diameter increases, the target surface heat transfer is also first augmented due to the increase in the flow reattachment and recirculation, and then it is decreased as the flow separation increases. The thermal performance indicates that the intensity of the heat transfer enhancement depends on the depth and diameter of the dimple.