| Gas turbine as aero-engine is usually likened as the aircraft’s heart. Throughout the development of aeronautics and astronautics technologies, every major progress was inseparable from the development of aero-engine design and manufacture technology. Due to the particularity of the aero-engine applications, there is no doubt that the design and manufacture of the aero-engine represents the most advanced technique and key development direction of modern power machinery. For this reason, the aero-engine techniques in every world power are very crucial, developed priority, monopolized highly, blockaded tightly, because the correlation techniques are seen to be one of the most important symbols of national military level, industry equipment and overall national strength. In our country, to meet the demands of supersonic and high performance aircraft, it’s imperative to investigate and improve a new generation of aero-engine.Under the premise of maintaining the same engine weight and dimension scale, one important approach to improve the engine efficiency is to increase turbine inlet temperature, but this approach is a double-edged sword. One hand side, a higher gas temperature at the inlet can bring a higher ratio of thrust to weight, but on the other hand side, the higher inlet temperature will result in a higher thermal load to the components exposed directly to extreme high temperature environment, especially to the turbine blade. Hence, more effective cooling methods must be developed to protect these components, and ensure the reliability and service life of the engine under long-term high temperature, high pressure conditions. At the beginning of turbine blade cooling design, only simple straight internal cooling channel was applied. Through several generations of cooling technique development, such as impingement cooling, film cooling and advanced film cooling, today the combination cooling techniques of internal ribbed channel and external film cooling have been widely used in modern gas turbine designs. However, more requirements of turbine blade cooling technique are still popular research topics, such as, how get optimal design of cooling structures to reduce the aerodynamic loss of the second flow? How achieve a reasonable cooling efficiency distribution with the least coolant consumption? Around these scientific questions deriving from the development of aero-engine gas turbine, numerous researchers have been carried out a lot of work in this field, since the invention of aero-engine. However, these topics are still very popular even nowadays.This dissertation will present a series of experimental and numerical investigations on the fluid flow and heat transfer characteristics of the internal cooling air channel and tip leakage of a typical turbine blade through the following three chapters.In the first section, the cooling air flow and heat transfer characteristics of the ribbed channels within a turbine blade were studied through experiments. Experimental platform was set up, and two different ribbed channels were designed, one channel is ribbed by inclined ribs installed on one wall, and the other channel by inclined ribs staggered installed on two opposite walls. Experiments were performed, and the aerodynamic loss, local and average heat transfer coefficients of the two channels was measured. The synthetical heat transfer efficiency of two structures was calculated and compared. The experimental data provide a reference for the designers of the ribbed channels, and can be used to validate turbulence models and calculation strategies in the numerical simulations carried out by our research group. Based on the experiments, according to the flow similar principles, a simplified optimization approach of the ribbed channels was proposed:during the first step of the optimization approach, the rib’s height e is fixed, but the rib’s pitch p is changed, the structure with the highest synthetical heat transfer coefficient was obtained by this step; in the second step, at the fixed p/e obtained by the first step, the rib height e is changed (but p/e maintains the value obtained by the previous step). Through the optimization of two steps, geometry parameters of a ribbed channel with the highest synthetical heat transfer coefficient can be obtained. The advantage of this optimization method is that it significantly reduces the work load of the ribbed channel design and improves work efficiency thereby.In the second section, an experimental and numerical investigation on tip leakage flow and blade tip heat transfer is presented. Two-dimension flow fields at the certain cross sections of turbine blade tip gap were captured by the PIV (Particle Image Velocimetry) system of USTC Engineering Experimental Center. Through the two-dimensional fluid flow fields, the generation and development of the tip leakage vortex of the turbine blade was analyzed. At the same time, a numerical simulation was carried out by commercial software. The numerical results obtained by five turbulence models were compared with the experimental data measured by the PIV. Through the comparison, the RNGk-ε model was suggested as the most close to the experimental data. Based on the experimental and numerical investigations, the effect of tip film holes injection to the tip leakage flow was numerical analyzed. To reduce the tip leakage flow using the cooling air injection through film holes, different arrangements and angles of the film holes were designed, and the corresponding cooling effectiveness and reduction effect of the leakage flow were compared through numerical simulations. Based on the numerical comparisons, this chapter provides the investigators and designers with a relatively comprehensive reference regarding turbulence model choice and tip film holes design to reduce leakage flow.In the third section, the effect of rotation and tip gap on blade tip heat transfer was numerically investigated. When investigating the characteristics of the fluid flow and heat transfer of the blade tip, three working states were used:1) both blade and endwall are stationary;2) the blade is stationary, but the endwall is rotating;3) the blade is rotating, but the endwall is stationary. The actual turbine blade worked under the third state, while resticted by experimental survey methods, most of the current experimental investigations were carried out under the first and second state. Great difference existed between the first two approximate experimental programs and actual turbine blade working condition, people doubted that whether the approximate program can accurately simulate the characteristics of flow and heat transfer on blade tip? How to select experimental program appropriately? To solve the controversy concerned with the experimental scheme of tip leakage flow, a typical GE-E3turbine blade was used as specimen, and numerical simulations were carried out at a rotating speed of8450r/min, three tip gap values0.3,0.75,1.2mm (1%,2.5%and4%of blade height respectively). The characteristics of the fluid flow and heat transfer of the blade tip gap were investigated under the three working states. Based on the numerical analysis, the better experimental schemes, which are more close to the real operation state of gas turbine rotor blade under different tip gaps, are suggested to investigators and designers of the experimental schemes of blade tip leakage flow and cooling performances. |
PDF Full Text Request