Experimental And Numerical Study On Cooling Performance Of Steam/air Flow In Cooling Blade

With the inlet temperature rising, the turbine blade cooling technology is also put forward higher requirements. For the traditional air cooling technology, Air is extracted from compressor and used to cool the hot end components. However, the mass flow rate of cooling air needs increasing with the technology of gas turbine developing, and it will result in reducing the efficiency of the compressor and also limiting the upgrading the power of gas turbine. In this context, steam cooling technology has been proposed. Steam cooling technology saves the high pressure air extracting from the compressor, and it has a great promoting effect for improving the compressor efficiency and overall efficiency of gas turbine. Therefore, the steam cooling technology is a new developing and having application prospect technology, which is also an important research direction in the study of cooling technology for gas turbine.In this paper, cooling performance of steam and air flow for several frequently-used cooling structure of turbine blade were experimentally investigated in similar working conditions. The 3-D numerical models of these cooling structures were also conducted. Based on the numerical results, the flow and pressure loss performances of the coolants were compared with each other. Results show that: heat transfer distribution of the two coolants have the similar characteristics. However, heat transfer performance of steam cooling is obvious higher than that of air cooling in the same cooling structure. But for different cooling structures, the advantages of cooling performance of steam cooling to air cooling are not the same. In the same Reynolds number condition, the area-averaged Nusselt number of steam cooling is about 13%-24% higher than that of air cooling in parallel rib roughened channel. In V-shaped and chamfering V-shaped rib-roughness channel, the area-averaged Nusselt number of steam cooling increases 19%-28% than that of air cooling.. When comparing them in the same mass flow rate condition, the advantage of steam cooling is greater. For steam and air cooling, the flow characteristics of them are similar in cooling channel, and the mechanisms of their heat transfer enhancement are also identical. The mechanism of heat transfer enhancement is that: the thermal boundary layer near heat transfer surface is thinning caused by strong secondary flow in cooling chamber, which result in heat transfer enhancement between coolant and heating wall. In the same Reynolds number condition, the pressure loss coefficients of the two coolants are almost equal. However, when in the consumption of the same flow rate condition, the pressure loss coefficient of steam cooling is lower than that of air cooling. The reason is that: the dynamic viscosity of steam is relatively lower, therefore, the friction loss generated by steam flow is also less.In order to investigate the cooling performance of a turbine blade scoured by high-temperature gas flow, an annular cascade test rig was built. The distribution of temperature on blade coating surface was measured by an infrared camera. The cooling performance of turbine blade cooled by steam and air flow were investigated and compared based on experimental results. The flow characteristics and pressure loss performance of the two coolants in internal chamber of blade were also analyzed based on a conjugate heat transfer numerical method. The thermal protecting effect of thermal barrier coating is also investigated based on numerical results. Results show that: distributions of cooling efficiency characteristics of turbine blade coating surface cooled by steam and air flow are similar, but those of blade surface cooled by the two coolant has minor difference. In steam cooling condition, the area-averaged cooling efficiencies of suction side of coating, pressure side of coating, suction side of blade and pressure side of blade are respectively 17.3%, 23.9%, 21.7% and 25.5% higher than those in air cooling condition. Thermal protecting effect of coating is very obvious, especially in steam cooling condition. If the steam flow injects into the blade channel after cooling the blade, it will get stronger interference on main stream and result in lower temperature comparing the air flow. That takes adverse effect on thermal efficiency improvement of the following turbine stage.