Vortex dynamics and thermal enhancement mechanisms in a turbine blade U-bend channel with coupled coolant extraction and delta winglet generators

The thermal protection of turbine blade tips is critical for engine efficiency. This study numerically investigates the flow topology and coupled heat transfer mechanisms in a U-bend cooling channel equipped with top endwall film cooling holes and delta winglet vortex generators (DWVGs). Using the Renormalization Group k-ε turbulence model, the interaction between the curvature-induced secondary flow (Dean vortices) and the DWVG-induced longitudinal vortices is analyzed across Reynolds numbers from 105 to 5×105. Results reveal that the strategic arrangement of DWVGs fundamentally alters the near-wall flow structure. Specifically, an array of four DWVG rows effectively disrupts the formation of the corner separation spiral node, thereby suppressing low-momentum recirculation zones and thinning the thermal boundary layer. Furthermore, increasing the DWVG attack angle to 75° intensifies the downwash effect of the streamwise vortices, which counteracts the cross-stream migration of the coolant and enhances convective mixing. The optimal configuration yields a 21.89% improvement in the Thermal Performance Factor compared to the baseline, attributed to the synergistic effect of vortex-induced shear stress enhancement and effective coolant coverage.