Influence Mechanism of Asymmetric Nozzle Gas-blowing on the Flow Field in Turbine Blade Film Cooling Holes during Ultrashort Pulse Laser Machining

Ultrashort pulse laser machining is pivotal for fabricating aero-engine turbine blade film-cooling holes because of its superior performance; however, machining residues can block the laser, reduce efficiency, and promote recast layer formation, thereby deteriorating component performance. Gas-blowing aids residue removal, but traditional symmetric nozzles easily form reverse flow vortices at hole entrances in high-aspect-ratio micro-hole machining, leading to secondary residue accumulation and reduced machining efficiency. This study numerically simulates coaxial auxiliary gas-blowing flow fields of symmetric and asymmetric nozzles, investigating the effects of their structural parameters. The results show that the symmetric structure has a stable flow field but limited residue removal improvement, while the asymmetric structure achieves directional flow-field optimization. Opposite-direction angles form a "swirling jet", which suppresses reverse flow vortices, expands the high-velocity region and enhances the flow flushing capacity. Compared with the same-direction angle configuration, the opposite-direction configuration reduces stable entrance recirculation and improves axial flow penetration into the micro-hole. The optimal parameters are m = ۲ mm, n = ۲ mm, θ۱ = ۱۰°, and θ۲ = -۱۰°, (m is defined as the throat length, n as the divergent-section length, and θ۱ and θ۲ as the inclination angles of the two opposite sides of the asymmetric divergent section.) which achieves the maximum flow flushing capacity. Under this condition, the total pressure loss across the shock structure is reduced to ۳۶.۴۴%, indicating weaker shock-induced energy dissipation and improved momentum transport inside the micro-hole. This study provides theoretical support for the high-precision machining of high-aspect-ratio film-cooling holes.

کلیدواژه ها:

Ultrashort pulse laser machining ، Film cooling holes ، Asymmetric nozzles ، Supersonic gas-blowing ، Flow flushing capacity