Investigation On Leading-Edge Film Cooling Of A Gas Turbine Guide Vane

Film cooling, as one of the cooling types, has been used in gas turbines for many years and proved to be an efficient method protecting blade or vane, especially the vicinity of the stagnation line, is a critical region because thermal load is at its highest in this area and particular protection and cooling design are required. The flow around the leading edge is always associated with mainstream stagnation, strong pressure gradient, variable curvature, and interaction between rows of showerhead holes. It is necessary to understand flow and heat transfer characteristics of the leading edge film cooling for achieving a reliable film cooling design improvement for gas turbines.In this dissertation, the experimental setup of film cooling on flat plates is configured firstly, and thermo-chromic liquid crystal is utilized to measure the temperature distributions downstream of the injection holes. Then we discuss the influences on film cooling brought by different blowing ratio, different injection hole length to diameter ratios and different injection angles, etc. The adiabatic film cooling effectiveness is regarded as an important parameter to weigh the cooling performance at different experimental conditions. Numerical simulations for film cooling characteristics on flat plat were also performed. Based on the experimental and numerical results, the investigations on the leading-edge film cooling of an inlet guide vane have been done. The original design is simulated to obtain flow mechanism and heat transfer characteristics of the leading edge film cooling. The film cooling characteristics and interactions between jets and mainstream around the leading edge, especially near the stagnation line, are analyzed in detail. To provide better coolant coverage on the leading edge, the cooling configuration is modified based upon the analysis and understanding of the 3D prediction for the original design. The modified designs are compared with the original design and provide better coolant coverage on the leading edge. The main conclusions of the dissertation are as follows:At a low blowing ratio, the secondary injection flow has low momentum compared to the mainstream, so it is easily suppressed by the mainstream to a region near the cooper plate surface. Better cooling performance can be achieved in the region immediately out of the injection holes. When the blowing ratio increases, the phenomenon of "blowing off" and "re-attachment" happen downstream of the film holes. At a low hole length to diameter ratio (L/D=2), the air flow cannot fully develop in the hole and the adiabatic film cooling effectiveness of are lower. The effect on the cooling performance due to different vertical velocity component is considered in connection with different injection angles downstream the injection hole. The results show that the contours still appear in a taper shape in the nearby region of the film hole at a low blowing ratio when only vertical velocity existsWhen the holes just locate on the stagnation line, the radial movement of the coolant is dominating only at the pressure side close to the holes. At the suction side close to the holes, the radial movements is weakened by mainstream accelerating. When the holes locate alongside the stagnation line, the circumferential movement of the coolant dominates. Better cooling effects at the stagnation line and both sides of the line can be obtained two intercross rows of holes at both sides of stagnation line and assuring that the stagnation line traverses the exit of each hole. It is necessary to avoid opposite jets occurring in the radial direction by changing the radial angles. It is difficult to obtain full coverage near the attachment node. Adopting lower blowing ratio and adding the circumferential distance to the attachment node can obtain better cooling better cooling effects. The modified design V is the best in the five designs.