For the ice protection of the engine air induction part manufactured with low thermal conductivity composite material, the combined heating method using interior impingement and exterior air film has certain advantages. To study the influence of the external jet air film on the impingement characteristics of droplets, the numerical simulation method of three dimensional water droplet impingement based on Eulerian method was developed and verified by experimental data from references. The droplets impingement characteristics under three different blowing ratios and two different velocities were then investigated based on the configuration of 3D cylinder with two parallel jet holes. Some effects of the jet air film on the droplet movement have been observed on different positions of the surface, including blowing off effect and diffusion effect, which means that the forward jet film will prevent the droplet from impacting on the surface and diffuse it from inner section to outer sections in span wise direction to decrease the local impingement coefficient. However, incoming air separation point on the surface will be also advanced due to the jet vortex behind the hole, which will increase the local impingement coefficient. Besides that, the increase in flow velocity will improve the momentum of droplets to weaken the effects of the blowing ratio to the distribution of local droplet impingement coefficient. This study about the effects of the jet film on the droplets impingement characteristics provides some reference to the design of ice protection system with exterior hot air film.
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