Experimental Investigations On Flow And Heat Transfer Characteristics Of Turbine Endwall

An important way to improve the performance and efficiency of aircraft engines can be achieved through higher turbine inlet temperatures. Now the turbine inlet temperatures are far beyond the limit of the heat-resisting ability of current turbine materials, therefore more efficient methods for cooling turbine components must be developed to maintain the safe and reliable operation of turbines.In recent years, as an important component of the turbine cascade, endwall cooling has received widespread attention. The complex secondary flows reduce the effectiveness of coolant injected along the cascade endwall, as well as increase endwall heat transfer. This research focuses on understanding the characteristics of flow in turbine cascade channel and heat transfer of film cooled turbine endwall.The main work of this thesis can be summarized as below:In a circular water tunnel with a low speed, the flow characteristics of a linear cascade without coolant injection were measured in detailed by a home-made TRPIV system. Based on statistical analysis of the large number of velocity fields, time-mean velocity and vorticity field as well as sampling point power spectrum in various measure-planes have been obtained. Through analysis of the time-mean and transient characteristics of secondary flow, the evolution process of secondary flow in the cascade was clearly revealed.To study the influence of coolant injection on the cascade channel flow, the secondary flow and concentration distributions of coolant fluid were obtained using the technique of TRPIV and PLIF, respectively. The flow nature of film cooling in the leading edge region was revealed by comparing the flow interaction between round hole and slot hole as well as the different structures of slot.In the last series of experiments, the high temperature working environment of turbine endwall was created through an electric-heating wind tunnel, and detailed measurements of the cascade endwall heat transfer were carried out using the technique of infrared thermal image. The heat transfer performances of the upstream cascade endwall were summarized by qualitative and quantitative analysis in view of mainstream Reynolds number and temperature, blowing ratio and temperature ratio of mainstream to coolingair, coolant injection angle and different film cooling structures.The main innovation points of this thesis can be concluded as following: The secondary flow in the turbine cascade exhibits the characteristics of strong unstability, which had been easily ignored by previous studies using time-mean measurements. Detailed measurements of secondary flow have been carried out by a home-made TRPIV system with high time resolution. With the help of the high time resolution, transient and time-mean characteristics of the secondary flow were obtained. The transient characteristics of the secondary flow can enrich the understanding of turbine cascade channel flow.The unsteady movements of horseshoe vortex could induce a high heat transfer area of leading edge endwall, where had been easily destroyed in the previous study. This thesis put forward an idea that slot holes are decorated in the upstream endwall. Under the influence of coolant flow, the formation of horseshoe vortex in leading edge were suppressed. Furthermore, the negative influence of secondary flow were weakened, and the endwall were cooled down at the same time.Most of the previous experimental studies regarding endwall film cooling were based on the assumption of adiabatic wall, and the corresponding experiments were most conducted under low temperatures by choosing low thermal conductivity materials, such as ceramic, organic glass. Our experiments have been carried out in a wind tunnel with high temperature mainstream, the specimens used in the experiments are made of high temperature alloy, the operation environment is more realistic, and therefore the measurement data are more valuable as references.