Research On Numerical Simulation Of Compound Impingement Cooling Characteristics

Along with increasing the thermal efficiency of the power devices such as gas turbine,the temperature of hot components rising. Cooling technology has become a key issuewhich restricts the gas turbine thermal efficiency and the initial temperature of the bladeinlet. Typical cooling technology mainly includes three categories, the film cooling andimpinging cooling and convection cooling. Impinging cooling technology, which is one ofthe most effective methods to obtain local heat exchange coefficient, has widely used tocool the hot components in gas turbine system. While the increased flame temperature willmake the traditional cooling technology more and more difficult. Therefore, a newpromising method seems to be valued for improving cooling effectiveness. Mist cooling is anew cooling method which uses phase transformation to obtain higher intensity of heatexchange. The evaporation of water droplet added in the coolant will increase temperaturegradient and lead to high convection between the target surface and the coolant. Thusresearch on the factors of influencing the impingement/mist compounded cooling willprovide effective guidance in reducing thermal load of hot components.Based on the urgent need of improving cooling effect, this study is focused on gasturbine transition piece. The model of transition piece was simplified to a double chambermodel with impinging holes in the outer-wall. Heat transfer augmentation in the coolantchamber was achieved through the numerical simulation about a series of mist/impingementcompound cooling patterns, which can be started as follows:Firstly, mist cooling simulation was carried out in the combustor liner using theDispersed Phase Model (DPM) of FLUENT. It turns out that the water droplet evaporationand particle tracks have been very good correspond with the references and verify the feasibility of mist simulation through DPM method.Secondly, the simplified double chamber model was established with multiple holesdistributed in the outer-wall. The Realizable k-turbulence model was studied andapplied to simulate the flow field with high temperature, velocity, and pressure conditions.The SIMPLE algorithm was adopted to discretize the governing equations.Then, the water droplets were introduced into the impinging cooling method, and theheat transfer augmentation performance of compound cooling technology was discussed inkinds of situations, which consist of five different mass flow rates and six kinds of dropletdiameters. Each situation was studied in single and multiple holes models respectively.Finally, two kinds of different cooling structures, which means the target surfacecurvature and the pin-fin structure, were taken as the factors that influence the coolingeffectiveness. And the Particle Swarm Optimization (PSO) was employed to research theimpinging cooling performance of the pin-fin governing parameters, such as detached spaceand diameter ratio. All the simulation results under various conditions reveal that themist/impingement compound cooling technology has a good performance in enhancing thecooling effectiveness and heat transfer.Results in this thesis came from comparative analysis between air impingement andmist/air impingement cooling ways in double chamber models. They indicate that the effortof adding some water droplets into the air will generate additional cooling effect. Theresults of numerical simulations provide a valuable reference for cooling structure design ingas turbine transition piece.