Assessing the effect of swirl flow on the film cooling effectiveness of a vane pressure surface

Strong swirling flow is an important characteristic that must be considered in the integrated design of combustors and turbines. The cooling pattern of turbine vanes obtained under the assumption of a uniform cascade inflow may not be able to guide the design of high-efficiency film cooling structures under swirling intake conditions. Therefore, it is necessary to carry out further research on the influence of inlet swirl on pressure surface film cooling and the mixing mechanism of jet and swirling flow. In this study, by considering varying swirl intensities and coolant flow rates, a steady-state pressure-sensitive paint (PSP) technology experiment was conducted to investigate the overall surface distribution of film cooling effectiveness (η) on a vane pressure surface. Comparative analyses of η differences between cylindrical and laidback fan-shaped holes were carried out. The results showed that swirling inflow leads to a radial pressure gradient at the pressure surface and radial deflection of streamlines at the wall surface. With the acceleration of airflow and the action of viscosity, the swirling core intensity weakens, and the influence of swirl inflow on the trailing edge region is gradually reduced. For the case of a weak swirl intensity, the sensitivity of the film trajectory distribution and η to the change in the freestream condition is minor, similar to that under the uniform inlet condition. On the other hand, strong swirl inflow can significantly enhance the radial deflection of the film trajectory; the uniformity of the η distribution decreases, and the relative standard deviation (RSD) increases by a maximum of 12.5 %. Increasing the coolant flow rate can relieve this phenomenon. The strong swirling flow characteristics also affect the laidback fan-shaped holes, and the radial deflection of the film is significant. The beneficial effect is that the dilation of the film-hole exit increases the extension ability of the film in the span and flow directions; the effective film coverage area is significantly increased. Compared with cylindrical holes, laidback fan-shaped holes increase the area-averaged η by 79.1 % and reduce the RSD by 20.5 %.