Research On Film Cooling Characteristic Of Converging Slot Hole

Film cooling plays a very important role in the cooling configuration of the modern gas turbine engines. A great deal of investigations focusing on the film cooling has been made, but the innovative technique enhancing the film cooling efficiency is also regarded as a challenging problem, of which the key is how to reduce the penetration of film outflow to primary flow and enhance the extensibility of film outflow along primary flow direction. Based on this research background, an innovation converging slot hole (console) film cooling configuration was studied in the present paper to further understand its flow and heat transfer characteristics. The content of the present investigation contains two main aspects. Firstly, for the plate console film cooling scheme, the flow and heat transfer performances of this innovative film cooling configuration is researched to reveal its physical mechanism for enhancing cooling characteristic, and the effects of film hole constructural parameters on the performance of film cooling are also studied to optimize the cooling film hole. Secondly, for the blade film cooling scheme, the study is made on the effects of primary flow Reynolds number, coolant blowing ratio and holes location on aerodynamic loss and heat transfer characteristics with converging slot film hole.The physical mechanism on film cooling enhancement of converging slot hole film cooling is investigated. The results show that the film outflow from converging slot hole is of inherent feature owing to its special internal flow passage, converging in streamwise direction and expanding in lateral direction, which behaives mainly that: (1) the secondary flow expands in the lateral direction and forms a pair of vortices originating from the converging slot hole sides, which is opposite to that from the cylindrical hole center. The alteration of vortice rotation direction makes the film coverage more uniform in lateral direction and prevents the primary flow from invading to the local area between film holes. (2) the secondary flow accelation insides the converging slot hole is benefit to promoting the film outflow spread along streamwise direction, and the secondary flow expanding in the lateral direction is capable of suppressing the film outflow penetration to the primary flow simultaneously, which makes the film outflow velocity distribution more reasonable, that is the film outflow peak velocity is promoted and the wall normal distance corresponding to film outflow peak velocity is reduced. Thus the adiabatic wall film cooling effectiveness for the converging slot hole is higher than that of the cylindrical film hole.The film cooling characteristics for the converging slot hole in a range of blowing ratios are studied, and the effects of converging slot hole parameters on the film cooling characteristics are analysed. Results show that the discharge coefficient and cooling effectiveness for converging slot hole increase with the increment of the blowing ratio. Under the same blowing ratio, the discharge coefficient and cooling effectiveness of the converging slot hole is higher than cylindrical hole, the advantage in improving film cooling effectiveness is more significant in the bigger blowing ratio case. In general, the relatively optimized geometry parameters on converging slot hole is 0.2d for slot width, 1.2d for hole height and 35°for inclination (here d is the diameter of film hole at inlet).Investigation on aerodynamic loss of turbine cascade with converging slot film cooling holes at blade suction surface is conducted for a typical cascade. The results show that both of the kinetic loss and total pressure loss coefficient of converging slot hole at different location increase with the increment of the coolant blowing ratio. With increment of the mainstream Reynolds number, the kinetic loss coefficient is reduced, while total pressure loss is increase. The kinetic loss and total pressure loss induced by the injection from film holes located at upstream of cascade throat are lower than that of the other locations, while the aerodynamic loss coefficients corresponding to downstream of throat locations are the biggest in most cases. The aerodynamic loss coefficients of converging slot hole at upstream of throat are lower than those of conventional round hole. If located at downstream of throat locations, the aerodynamic loss coefficients of converging slot hole might be higher than cylindrical hole in some cases.The film cooling effectiveness of converging slot hole at different location on the blade suction surface increases with the increment of the primary flow Reynolds number and coolant blowing ratio. Under the same condition, the cooling effectiveness of converging slot hole at upstream of blade cascade throat is almost higher than that of the other location. Compared with the cylindrical hole, the converging slot hole cooling effectiveness is improved obviously and more uniform in lateral variation at all locations. Heat transfer coefficient ratio of converging slot hole also increases with the increment of the primary flow Reynolds number and coolant blowing ratio. The heat transfer coefficient ratio of converging slot hole is higher than that of cylindrical hole at every situation.Compared with the cylindrical holes, the converging slot holes at upstream of blade cascade throat has lower aerodynamic loss coefficient and higher cooling effectiveness. It is indicated that perfect aerodynamics and film cooling characteristics could be obtained when the converging slot holes are set at blade cascade accelerated region.