Experimental and numerical investigation of heat transfer and friction performance for turbine blade tip cap with combined pin-fin-dimple/protrusion structure

The blade-tip region of turbine blade exposes to gas with high temperature and high velocity. So the cooling in this area has significant influence on turbine blade safety. The U-shaped cooling channel with 180° turning bend is common in internal cooling of turbine blades, which improves the heat transfer coefficient. Special attention should be paid to the impingement cooling at bend area which is important to the cooling of the blade tip region. Dimples, protrusions and pins which are placed on the bend area are well recognized to enhance the heat transfer in the area. In this paper, the heat transfer and friction performance of the tip-cap are predicted numerically and experimentally. Pin-fin-dimple/protrusion is arranged as the heat transfer augmentation structure at the bend region. It is concluded that, the temperature of solid surface decreases obviously when dimple/protrusion or pin-fin-dimple/protrusion structure is arranged. The area-averaged Nu of impingement surface with pin-fin-dimple/protrusion increases by 31.2-127.3%, which implies that the heat transfer performance is prominently better than that on the smooth tip wall. The additional pressure penalty of pin-fin-dimple/protrusion is 16.2% at most. In summary, the arrangement of dimple/protrusion and pin-fin-dimple/protrusion on the blade-tip surface inside the blade can enhance the heat transfer with little increase of friction, indicating an efficient cooling structure.