Investigation On Film Cooling And Combined Cooling Using Conjugate Heat Transfer Method

A variety of combined cooling configurations applied to modern gas turbine vanes have been developed, including film cooling, convection cooling and impingement cooling. It is very significant that using conjugate heat transfer (CHT) method to predict the temperature distribution and heat transfer characteristics of turbine vane surface, as well as employing multi-field coupled analysis to evaluate the cooling structure. The combination of experimental research and numerical simulation is performed on the investigation of overall cooling effectiveness (OCE) and conjugate interface heat transfer through film cooling and combined cooling flat plate. Multi-field coupled simulation and analysis are carried out to evaluate the combined cooling flat plate.A conjugate flat plate and a thermal infrared imager imaging and processing system are established. The temperature distribution on the conjugate surface of film cooling and combined cooling flat plate is measured to obtain the OCE distribution.The influences of blowing ratio, film hole configuration and Biot number on the OCE and conjugate interface heat transfer in film cooling and combined cooling are investigated based on CHT method. According to the experimental and numerical results, the OCE on the whole conjugate interface is always positive. Upstream the film holes, the OCE increases with the increase of blowing ratio. Downstream the film holes, the OCE is the highest at low blowing ratio when using cylindrical holes, while the OCE is higher at high blowing ratio for fan-shaped holes than other holes. The decrease of Biot number makes the OCE distribution more uniform on the conjugate surface, and leads to the reduction of the area where the interface heat flux is positive. Compared to film cooling method, the combined cooling obviously improves the cooling effect of the conjugate surface. As the blowing ratio increases, the OCE on the conjugate interface in combined cooling becomes higher. For combined cooling, using fan-shaped holes in film cooling flat plate could provide a better cooling performance than using cylindrical holes at a high blowing ratio. The impingement hole arrangement and the distance from the impingement hole outlet to the target surface also affect the OCE distribution. When Biot number reduces, laterally averaged OCE distributes more uniform upstream the outlet of film holes. However, Biot number has a slight impact on downstream OCE distribution and the interface heat transfer coefficient distribution.Multi-field coupling method is utilized to evaluate the combined cooling flat plate upon thermal stress. The impact of blowing ratio, film hole configuration and impingement structure on thermal stress concentration is investigated. The results indicate that thermal stress concentration mainly appears around the film holes and will become more obvious with the increase of blowing ratio. Thermal stress concentration is also affected by the impingement structure.