Effect of weak swirling flow on film cooling performance

Experiments have been performed in a large circular pipe to study and obtain the film cooling effectivenesses with the presence of weak swirling flow in the mainstream. The swirling flow is generated by aflat vane swirler situated upstream. Cooling film is injected from an annular slot formed by the pipe wall and the circular cover plate. The radial temperature distribution measurements at several axial locations were used to infer the rate of mixing of film jet with swirling flow. The swirl number, which increases with turbulence intensity and swirl velocity in the mainstream, can significantly increase the mixing rate of film jet with swirl flow and decrease the film cooling effectiveness. During the course of the experiments, the blowing ratio ranged from 0.5 to 1.75 and the swirl number ranged from 0 to 0.6. Correlation equations for the film cooling effectiveness, which account for the effect of swirling flow, are obtained.