Influence mechanism of wall cooling on boundary layer characteristics in high-loaded low pressure turbine cascade

The complex thermal environment of high-loaded low-pressure turbines poses significant challenges to accurate boundary-layer prediction, particularly under low-Reynolds-number operating conditions where laminar separation bubbles (LSBs) are prevalent. Most previous studies neglect wall heat-transfer effects and therefore deviate from realistic engine conditions. In the present work, large eddy simulation (LES) is employed to investigate the influence of wall cooling on boundary-layer transition and loss generation in a highly loaded low-pressure turbine cascade at Reynolds numbers of 50,000 and 100,000. The results show that wall cooling significantly shortens the laminar separation bubble and promotes earlier transition. Rather than attributing this behavior solely to changes in fluid viscosity, the transition enhancement is interpreted using the momentum-thickness Reynolds number at separation, R e θ , s .Wall cooling increases R e θ , s , thereby shifting the separated shear layer toward a more unstable regime. Spectral analysis of pressure fluctuations reveals dominant frequencies whose corresponding Strouhal numbers fall within and slightly extend the range reported in the literature reported for Kelvin–Helmholtz instability in separation-induced transition. This confirms that Kelvin–Helmholtz instability governs the initial breakdown of the separated shear layer under both adiabatic and cooled conditions. Furthermore, wall cooling suppresses vortex roll-up intensity and turbulent fluctuations, leading to substantial reductions in profile loss, particularly at lower Reynolds numbers. These findings clarify the physical mechanism by which wall cooling influences separation-induced transition and loss generation in high-loaded turbine cascades, providing guidance for thermal management strategies in advanced turbine design. • Wall cooling increases the momentum-thickness Reynolds number at separation, leading to earlier shear-layer instability. • The laminar separation bubble length is reduced by up to 30.6% under cooled wall conditions. • Strouhal-number analysis confirms Kelvin–Helmholtz instability as the dominant transition mechanism. • Wall cooling suppresses vortex roll-up intensity and reduces profile loss by 24.6–36.1%.