Mechanism of supersonic blowing flow field in ultra-fast laser drilling film cooling hole in turbine blade

Due to high precision and non-contact advantages， ultrafast laser drilling is widely applied in precision hole machining. During drilling process， assist gas is used to enhance machining quality and efficiency. Regarding the blowing flow field during ultrafast laser processing of film cooling holes in turbine blades， the impacts of parameters such as gas assisted methods， inlet pressure， and modified nozzles on the shock wave structure were investigated. The results indicate that： both coaxial and paraxial gas assistance have normal shock wave， coaxial also has shock diamonds， paraxial flow yields higher hole velocity， benefiting machining. Increasing inlet pressure strengthens shock wave， expands affected area， and raises peak Mach number. Larger nozzle diameters extend shock wave expansion， lower normal shock and diamond positions， and shrink the second normal shock and diamond scopes. When the nozzle is modified into an elliptical shape， the shock wave structure no longer distributes symmetrically. As the aspect ratio of the ellipse increases， the shock wave affected area expands， Ma=1.95 equivalent surface shift from inverted bell to conical， and shock diamonds vanish. Modified nozzles introduce swirling flow to weaken shocks， improving fluid mixing and hole velocity. The swirl nozzle with four vortex generators ejects metal residues better， enhancing drilling quality and efficiency. In comparison， variations in inlet pressure and nozzle diameter mainly influence the shock wave intensity and range， while the nozzle shape exerts the most prominent impact on the shock wave shape and structure.