Research On Mist/Air Cooling Enhancement Techniques Of Turbine Blade

To improve the overall thermal efficiency, the inlet temperature and compressor pressure ratio are increasing for the next generation of gas turbine systems. As a result, gas turbine engines are expected to continuously operate at temperatures much higher than the allowable metal temperature of the turbine blades, which, in turn, makes effective cooling of the blades essential. Therefore, new cooling techniques are essential for surpassing these current limits. One of the promising techniques is to enhance cooling with mist injection. There are two enhancement mechanisms for mist/air cooling. One is that latent heat of evaporation serves as a heat sink to absorb large amounts of thermal energy,the other is that steam&water have higher specific heat capacities than air.This paper investigates the potential of turbine blade’s cooling enhancement techniques by injecting water mist into the cooling air:1. The ANSYS-CFX software is used to simulate NASA-MarkⅡ high pressure air-cooled gas turbine.Using the experimental results, the CFD model has been tuned by employing different turbulence models, transition models. Comparing to the experimental results, k-ω-SST-γ-θ turbulence model results are more accurate and can simulate accurately the flow and heat transfer characteristics of turbine with transition flow characteristics. In addition, the effects of various parameters including conjugate heat transfer, cooling air, temperature of mainstream flow, turbulence intensity of mainstream, and incidence angle are also studied.2. Two-phase CFD calculations, using a Lagrangian model and commercial code ANSYS CFX, are employed to calculate the gas and droplet flows and heat transfer characteristics with and without mist on the blade surfaces. The Temperature of blade surface and distribution of evaporated steam on the surface of internal cooling passage are presented. And then, a compound cooling blade with film cooling and convection cooling techniques is aquired which is modified from the blade of MarkⅡ. The Cooling Enhancement performance pre or after injecting mist at the inlet of cooling cavity is investigated.3. The k-ω-SST-γ-θ turbulence model is adopted to solve conjugate heat transfer problem of C3X three-dimensional film cooling turbine blade.Operating condition under elevated gas turbine conditions are simulated and compared.By injecting mist into the cooling air at the inlet of three different cavities located on the leading edge, pressure surface and suction surface, the Cooling Enhancement performance of the blade is researched.The effects of various parameters including mist concentration, water droplet diameter, incidence angle of mainstream flow, temperature of mainstream flow, and droplet wall boundary condition are investigated. The CFD model employed the Discrete Phase Model (DPM) including both wall trap and droplet reflect conditions. The Temperature on blade surface, the evaporated steam concentration distribution at the whole turbine passage, and predicted metal blade Temperature distribution at mid-span are presented. The centreline temperature and distribution of cooling effectiveness on the surface of metal blade are also presented.