Investigation of heat transfer in a return-flow impingement cooling scheme considering micro-ribs and target surface shape

As a critical piece of equipment for energy applications, gas turbines face challenges from the extreme high-temperature environments at their turbine blade leading edges. Although return-flow impingement cooling is an advanced and highly efficient technology, studies on the effects of micro-rib and target-surface shape on heat transfer characteristics remain scarce. An investigation is conducted into the effects of micro-rib layout, micro-rib height, and target surface shape on heat transfer characteristics. The results reveal that the asymmetric micro-rib layout deteriorates heat transfer on the target surface, whereas the symmetric micro-rib layout enhances it. The micro-rib layout further affects the heat transfer performance of the target surface through its regulation of PV (primary vortex) development within the impingement cavity. The symmetric micro-rib layout enhances target-surface heat transfer, yielding a 3.2% increase in normalized Nu relative to the smooth surface, while greater micro-rib height further improves heat transfer for all layout schemes. Target surface shape governs the evolution of PV and SCRV (secondary counter-rotating vortex), thereby modifying the Nu distribution. The double-swirl structure exhibits superior heat transfer performance and more favorable pressure loss characteristics, and its TPF (thermal performance factor) reaches 2.87. However, the distorted vortex structures over the actual turbine leading edge target surface lead to deteriorated heat transfer and an asymmetric Nu distribution, resulting in TPF of only 2.07.