Heat transfer evaluation of return-flow impingement cooling considering inclined sidewall and conical return hole

Impingement cooling techniques are extensively utilized on the turbine blade leading edge to mitigate thermal load. This study is an extend of an anti-crossflow return-flow impingement cooling scheme. In this study, the effects of inclined sidewalls and return holes are numerically studied with jet Reynolds number varying from 5,000 to 15,000. Three sidewall schemes (vertical, inward inclined, and outward inclined) and two return hole shapes (constant cross section and conical cross section) are investigated and compared. Numerical results show that by inclining the sidewalls, the interaction and scrape effects from return flow on the sidewalls are changed, causing heat transfer performance and pressure loss vary. To be specific, as the sidewalls are inclined inwards/outwards, the heat transfer is enhanced/weakened accordingly, making a maximum increase by 12.9% and maximum decrease by 14.3% compared to the origin design. The introduction of conical return holes contributes to improving upwards velocity of return flow and subsequently enhancing scraping effects on sidewalls. For case with vertical sidewalls, inward-inclined sidewalls, and outward-inclined sidewalls, the area-averaged Nusselt number is maximum increased by 47.2%, 61.9% and 25.7% with the application of conical return holes.