Research On Tip Leakage Flow And Heat Transfer In Turbine Blade

Turbine tip leakage flow is one of the most seriously factors which affect engine performance. How to inhibit the leakage flow effectively and cool blade tip is very important to improve the efficiency and reliability of the turbine. This article investigates the generation mechanism of the tip leakage, the impact of tip geometry and flow parameters on the tip leakage flow and heat transfer which based on aero-engine turbine tip leakage flow control technology and cooling technology.Firstly, leakage flow and heat transfer of non-jet flat tip were studied by numerical simulation. This part of study includes leakage flow structure, the total pressure loss coefficient of the cascade exit plane and blade tip heat transfer coefficient distribution. The effects of tip clearance height, the cascade inlet flow parameters and the casing relative motion on the tip leakage flow and heat transfer were detailed studied. The results have showed that: the tip region will form tip separation vortex and leakage vortex thanks to the tip leakage flow. The tip separation vortex has a small reach,however the leakage vortex’s influence can reach about 75% span of the tip region. The heat transfer coefficient of the leading edge of the blade tip, middle, pressure side and suction side in the tip region is higher, which affected by the tip leakage flow. The clearance height’s impact on flow and heat transfer characteristics of leakage flow is significant. As the clearance height increases, the mass flow that come through the clearance increases linearly, the aerodynamic efficiency decreases linearly, the total pressure loss coefficient increases, the heat transfer coefficient increases. The effect of the cascade inlet parameters is very weak. With the increase of the inlet flow angle, the mass of the leakage flow decreases, aerodynamic efficiency increases, total pressure loss coefficient decreases, heat transfer coefficient decreases. As the free-stream turbulence increases, the leakage flow increases, the aerodynamic efficiency decreases, the total pressure loss coefficient increases, the heat transfer coefficient increases. The relative rotation of the casing will reduce both the leakage flow and the total pressure loss coefficient by 10%, increase the aerodynamic efficiency by 0.16%, reduce the tip heat transfer coefficient by about 5%.Secondly, the tip leakage flow and heat transfer of blade with squealer or wing tip was investigated numerically. A detailed study of the geometry parameters on the flow and heat transfer was investigated. The results have showed that: leakage flow form a intense vortex in the cavity of the squealer blade tip, hence increase the static pressure within the gap, which is the nature that leakage flow adds flow resistance. Compared to the flat tip, the squealer can increase the aerodynamic efficiency and decrease tip leakage flow and total pressure loss coefficient. But leakage flow in the cavity will result in severe disturbance, thereby increasing the heat transfer coefficient of tip. As the clearance height increases, the aerodynamic efficiency of blade with squealer or wing tip decreases, the mass flow and total pressure loss coefficient increases. Increasing the height of squealer increases the flow resistance, but the height has an optimum value. With higher squealers, the heat transfer coefficient becomes higher. The squealer width has little effect on leakage flow and heat transfer. The winglet tip can decrease the leakage flow and total pressure loss coefficient by preventing the radial flow. For the winglet tip, heat transfer coefficient on the tip show relatively low values, but the pressure side wing has high heat transfer coefficient itself.As the wing width increases, the flow resistance increases, but the wing has high heat transfer coefficient itself. The wing height has slight effect on leakage flow and heat transfer.Then, leakage flow and heat transfer of cooling jet tip were studied by numerical simulation. The effects of flat tip jet holes locations, jet angle, blowing ratio and other parameters on the aerodynamic efficiency, leakage flow, leakage losses and film cooling effectiveness were studied carefully. As a comparison, leakage flow and heat transfer of squealer tip and winglet tip with cooling jet were also investigated. The results have showed that: leakage flow of blade tip with and without cooling jet is similar. Compared with the case of non-jet tip, tip with cooling jets has a higher aerodynamic efficiency, lower leakage flow rate and higher total pressure loss coefficient. Film cooling efficiency can be seen only downstream the holes. However, film cooling efficiency of the tip leading edge, pressure side and the suction side near the leading edge is low. These are not film covered areas. When changing the holes locations, pressure side injection has the highest film cooling efficiency, lowest leakage flow rate and total pressure loss coefficient. When changing the jet angle, the 90 ° jet holes have the highest aerodynamic efficiency, lowest leakage flow rate and total pressure loss coefficient. As the jet angle increases, film cooling efficiency decreases, which means the effect of the jet cooling deteriorates. As blowing radio increases, aerodynamic efficiency increases, leakage flow rate decreases, total pressure loss coefficient increases, film cooling efficiency increases.Flat tip,squealer tip and winglet tip with cooling jet will increase aerodynamic efficiency, reduce leakage, increase total pressure loss coefficient. The squealer tip has best performance,flat tip has worst performance. The squealer tip film cooling effectiveness lower than the flat tip when the blowing ratio was less than 1.1, and the squealer tip film cooling effectiveness higher than the flat tip when the blowing ratio was higher. The winglet tip film cooling effectiveness higher than the flat tip. Flat tip,squealer tip and winglet tip film cooling effectiveness increases as blowing ratio increases.Finally, the flow field of tip clearance in an typical turbine shroud with film cooling flow was studied by PIV system. Leakage flow and heat transfer of the shroud tip were studied by both experimental method and numerical simulation. The effects of shroud tip clearance height, leakage flow Reynolds number, outflow ratio of the former and the latter holes on the total pressure loss coefficient and heat transfer coefficient was investigated. The results have showed that: there is a low velocity area in the shroud cavity. It is because the coolant injected from the former and latter holes increases the local pressure in the cavity, thus reduce the leakage flow. Former and the latter injection both have blockage effect on the leakage flow. As the outflow ratio of the former and the latter holes increases, the blockage effect increases. Total pressure loss coefficient increases as mainstream Reynolds increase, the averaged heat transfer coefficient increases. As the outflow ratio of the former hole increases, total pressure loss coefficient increases, but the outflow ratio of the latter hole has little effect on total pressure loss coefficient. As the outflow ratio of the former and the latter holes increases, the heat transfer coefficient increases, and the effect of the former hole is more significant. With the decrease of the clearance height, the total pressure loss coefficient increases. And under small gap, the total pressure loss coefficient with leakage flow Reynolds number and the outflow ratio of the former hole increases rapidly. As the clearance height decreases, the heat transfer coefficient increases, and the heat transfer coefficient decreases rapidly when the gap decreases.