Numerical analysis of cooling efficiency for turboshaft engines with converging-diverging film cooling holes

Higher power-to-weight ratio of turboshaft engines face a challenge that the temperature exceeding the allowable temperature of combustor, consequently the quest of more efficient cooling technologies has been a longstanding urgent pursuit. To boost the heat transfer efficiency, the traditional cylindrical film holes in cooling structures are replaced with a converging-diverging shape in the present work, and the heat transfer process as well as the gas flow is numerically simulated. In contrast to the cylindrical film holes, the converging-diverging holes have an excellent improvement in film cooling effectiveness. The maximum aperture, inclination angle, and blowing ratio of the converging-diverging hole show a main influence on the separation motion in the hole, which governs the film cooling effectiveness downstream and the vortex structure. Besides, the converging section is proved to increase the fluid speed in the hole while the diverging section brings the cold fluid closer to the combustor liner. According to the numerical analysis, the best film cooling effectiveness is obtained by setting the maximum aperture, inclination angle, and blowing ratio as 0.8 mm, 30°, and 1.5, respectively. As a result, the converging-diverging holes can dramatically reduce the wall temperature by 100 K. The proposed converging-diverging hole provides a new avenue for the film cooling techniques and can be treated as a preliminary design of highly efficient cooling approach for turboshaft engines.