Experimental study for the effect of typical hole geometric deviation on film cooling effectiveness

• Defined and measured film-hole straightness & convergent-taper deviations. • Diameter/jet angle/taper/straightness deviations reduce cooling effectiveness by 13 %/24 %/60 %/30 %. • Holes manufacturing process should minimize jet angle and straightness deviations. The hole geometric deviations (including diameter deviations (△ D / D ref ), injection angle deviations (△ α ), taper angle deviations ( β ) and straightness deviations ( γ in and γ out )) were unavoidable in cylindrical hole manufacturing via Electrical Discharge Machining (EDM) and Additive Manufacturing Technology (AMT) processes. 210 holes by EDM and 270 holes by AMT were processed to obtain the true and reliable geometric deviation parameters. Through industrial CT scanning, the geometric structure features of each hole were obtained, and each geometric deviation size was obtained by the image contour recognition method. Pressure-sensitive paint (PSP) thermographic measurement was employed to investigate the influence degree and flow and heat transfer mechanism of each geometric deviation. Results establish control requirements for each geometric deviation to prevent cooling performance degradation: diameter deviations should be at least greater than 0; injection angle deviations should be avoided as much as possible; taper deviations tolerance could be relaxed and strategic toward diverging geometries ( β > 0) was better when manufacturing limitations exist; straightness deviations should be minimized as much as possible. At higher blowing ratios ( M ≥ 0.75), area-averaged film cooling effectiveness increased monotonically with diameter expansion (△ D / D ref = -5% to 25 %). However, △ D / D ref ≤ 10 % still caused more than 2.3 % effectiveness reduction at low blowing ratio ( M = 0.5). Injection angle deviations (△ α = −1.5 ° to 1.5 ° ) consistently degraded the film cooling effectiveness, with degradation magnitude increasing to deviation increasing. Single straightness deviations had a greater attenuation effect on cooling performance, among which outlet straightness deviations exhibited stronger degradation.