Enhancement of film cooling effectiveness fed by internal crossflow using inlet expansion standard shaped hole

Abstract

Recent efforts have highlighted asymmetric and deteriorated coolant distribution behind crossflow-fed shaped holes, primarily due to in-hole vortical structures. In this study, inlet-expansion standard-shaped hole (IESSH) is proposed and investigated using large eddy simulation at channel-to-mainstream velocity ratio of ${\mathrm{VR}}_{\mathrm{ch}}$ = 0.3–––0.7, coolant-to-mainstream velocity ratio of ${\mathrm{VR}}_c$ = 0.4–––1.2, and corresponding inlet velocity (channel-to-coolant) ratio of ${\mathrm{VR}}_{\mathrm{in}}$ = 0.15–––1.75. Results show significant performance improvements for inlet-expansion at the windward, leeward, and forward hole edges. While the standard shaped hole serves as the baseline with degraded and biased coolant distribution, the IESSH design demonstrates symmetric coolant spreading and higher effectiveness. Specifically, the IESSH design exhibits wider and stronger vorticity at the entrance, enhancing coolant ingestion from both top and bottom channel flows, particularly at lower inlet velocities. Higher ${\mathrm{VR}}_{\mathrm{in}}$ values lead to lower discharge coefficients, resulting in insufficient coolant and reduced effectiveness, whereas lower ${\mathrm{VR}}_{\mathrm{in}}$ values feature higher discharge coefficients, improving coolant distribution. Notably, the IESSH design consistently shows higher discharge coefficients and cooling effectiveness, especially in transition and mixing regimes (${\mathrm{VR}}_{\mathrm{in}}$ > 0.45). An operating range of 0.4 < ${\mathrm{VR}}_{\mathrm{in}}$ < 1.5 is recommended for efficient performance, where the IESSH leverages enhanced coolant momentum. Very low ${\mathrm{VR}}_{\mathrm{in}}$ (${\mathrm{VR}}_{\mathrm{in}}$ < 0.25) values can lead to inefficiencies due to higher momentum and coolant lift-off. The findings provide valuable insights into the relationship between hole-inlet geometrical configurations and flow conditions, promoting advancements in cooling technology.