Numerical study on flow and heat transfer characteristics of swirling jet on a dimpled surface with effusion holes at turbine blade leading edge

In this paper, a numerical study has been conducted on the effect of the offset of jet holes on the flow structure and heat transfer of swirling flow in a concave target chamber with various dimple structures and effusion holes at the turbine blade leading edge. The ratio of jet holes off the centerline distance to jet hole diameter (e/d) varies from 0 to 2.0, and the ratio of jet-to-target plate spacing to jet diameter (H/d) is 4. The effusion hole diameters of 0.5d are arranged in a staggered pattern relative to the jet holes. Four types of dimple structure with a large depth ratio (delta/D) of 0.25, including spherical dimples (SDs) and oval-trench dimples (OTDs) in an in-line and staggered arrangement, are considered. The heat transfer characteristic and pressure loss of the different leading-edge are evaluated and compared at a Reynolds number of 30,000 based on the jet hole diameter. The results show that the offset of the jet holes provides 15%-higher overall heat transfer performance and more uniform heat transfer of the target surface, while having little impact on the friction factor within the e/d range of 0-2.0. The introduction of the dimple structures on the target surface decreases the overall averaged Nusselt number but enhances the total heat transfer rate from the target chamber due to the clear increase of heat transfer areas, for which a maximum of a 24% improvement of the thermal-hydraulic performance is obtained for e/d = 2.0 with OTDs in a staggered arrangement. Under the same e/d, the OTD structure, especially with the staggered arrangement, is superior to the SD structure.