Experimental optimization of novel B-shaped and C-shaped holes on flat plate and linear cascade models

This study experimentally optimized B-shaped and C-shaped holes on the flat plate and linear cascade models to maximize cooling effectiveness. Adiabatic cooling effectiveness was measured via Pressure-Sensitive Paint experiments, and Response Surface Methodology was used for cooling effectiveness prediction. Additionally, Particle Image Velocimetry experiments were conducted to analyze the flow field. Film holes were arranged on the flat plate and at four streamwise positions of the vane, with a 45° injection angle and no compound angle. Blowing ratios ranged from 0.5 to 2.5 at a density ratio of 1.5. The mainstream Reynolds number based on hole diameter was 10⁴ for flat plate experiments, and 10⁶ based on chord length for cascade experiments. Optimization results further demonstrate the cooling potential of both curved expansion holes. B-shaped holes achieved a maximum effectiveness improvement of 29.6%, while C-shaped holes reached 46.7%. Optimized B-shaped and C-shaped holes suppressed coolant lift-off and achieved full film coverage. The enhanced performance is primarily attributed to the increased spanwise outlet width, which induces jet bifurcation and significantly strengthens lateral coolant spreading via intensified anti-counter-rotating vortex pairs. Optimization effectiveness was highest on the suction side, followed by the flat plate, and lowest on the pressure side. The influence of structural parameters on cooling effectiveness is independent of wall curvature, enabling the application of flat plate optimization results to the vane.