Research On Single Row Film Cooling And Full Coverage Film Cooling

Film cooling plays a very important role in the cooling configuration of the flame tube and turbine blade for the modern gas turbine. 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 reduces the penetration of film outflow and increases the film coverage region on the wall. Aiming at the objective to enhance the film cooling efficiency, the content of the present investigation contains two aspects. Firstly, for the single row film cooling scheme, an innovative concept using ridge-shaped tabs at upstream edge of film holes to improve film cooling efficiency is present. And the numerical simulation and experimental study is made on the flow and heat transfer performances of this innovative film cooling configuration to reveal its physical mechanism for enhancing cooling characteristic. Secondly, for the full coverage film cooling scheme, the numerical simulation and experimental validation is made to study the effects of holes array arrangement, holes area percentage and blowing ratio on the performance of film cooling. And the optimization of cooling film holes array arrangement is conducted.The physical mechanism on film cooling enhancement of ridge-shaped tab inside film hole is investigated. The results show that the existence of ridge-shaped tab affects the flim outflow field, which make the film outflow velocity distribution more reasonable. One aspect, the film outflow peak velocity is promoted. And the anather aspect, the wall normal distance corresponding to film outflow peak velocity is reduced. The ridge-shaped tab is capable of suppressing the film outflow penetration to the primary flow, but also capable of promoting the film outflow spread along lateral and streamwise direction. Thus the adiabatic wall film cooling effectiveness for the film holes with the ridge-shaped tabs is higher than that of the conventional round film holes.The performance of flow and heat transfer for the film holes with ridge-shaped tabs is investigated numerically and experimentally. The effects of ridge-shaped tab parameters on the adiabatic wall film cooling effectiveness, convective heat transfer coefficient and discharge coefficient are concluded. In the case of a suitable tab blocking ratio range, the effect of ridge-shaped tab on suppressing film outflow penetration is more obvious under a bigger blowing ratio or tab blocking ratio, which is benefit to improve the adiabatic wall film cooling effectiveness. Once the tab blocking ratio is too big, the film outflow near the film hole will separate seriously as well as the primary flow and the secondary flow will mix rapidly, which leads to a reduction of the adiabatic wall film cooling effectiveness. Thus, the optimal tab blocking ratio is corresponding to the blowing ratio. In a general way, for the small blowing ratio, the optimal tab blocking ratio is small, and the optimal tab blocking ratio increases as the blowing ratio increases. As the tab blocking ratio increases, the convective heat transfer coefficient increases and the discharge coefficient decreases. The flow and heat transfer characteristics for expand-shaped film holes with ridge-shaped tabs are investigated numerically and experimentally. The effects of ridge-shaped tab and expand-shaped hole parameters on the adiabatic wall film cooling effectiveness, convective heat transfer coefficient and discharge coefficient are concluded. The change of the streamwise expanded angle or the laterally angle results in the change of the kidney vortex pair pattern. Both are all benefit to improve the adiabatic wall film cooling effectiveness of the expanded film holes. In comparison, the effect of the streamwise expanded angle on the adiabatic wall film cooling effectiveness is prominent to that of the laterally angle. As regard as the coordination of the ridge-shaped tab and expanded shaped film hole, the effect of ridge-shaped tabs coupled with laterally expanded film holes is obvious on the adiabatic wall film cooling effectiveness improvement, but the ridge-shaped tabs coupled with streamwise expanded film holes has little effect on improvement of the adiabatic wall film cooling effectiveness.The adiabatic wall film cooling effectiveness, convective heat transfer coefficient on the cold side and film side, discharge coefficient for the full coverage film discrete holes wall are studied numerically. The effects of the film holes array arrangement, the holes area percentage and the blowing ratio on the performance of flow and heat transfer are concluded. The results show that the holes array arrangement with long hole to hole downstream distance and short hole to hole lateral distance is the optimal arrangement. Under this arrangement, the penetration of film outflow is weaker and film coverage region is larger. The blowing ratio is the most important parameter affecting the convective heat transfer coefficient on the cold side and the film side. As the blowing ratio increases, the convective heat transfer coefficient increases. Accroding to the film formation and development features, a concept of developed film stage is put out in the present thesis. The film row number corresponding to the developed film stage and the adiabatic wall film cooling effectiveness relations are summarized. Furtherly, the correction considering the influence of temperature ratio between the primary flow and secondary flow on the adiabatic wall film cooling effectiveness relations is also made.The numerical calculation and experimental vadilation are conducted on the total cooling effectiveness of the full coverage film discrete holes wall. The effects of the film holes array arrangement, hole diameter, holes area percentage and the blowing ratio on total cooling effectiveness of the full coverage discrete holes wall were concluded. The result shows that the total film cooling effectiveness is consistent with the adiabatic wall film cooling effectiveness, that is the holes array arrangement with long hole to hole downstream distance and short hole to hole lateral distance is also the optimal arrangement.