| Gas turbines have been widely used in power and energy industries, but the compressorof a gas turbine consumes as a rule of thumb about1/2-2/3of useful turbine expansion work,which decreases the output of power turbine. Therefore, to reduce the compressor workbecomes one of the most effective ways to increase the gas turbine output power. Wetcompression within gas turbines becomes the most popular technique in recent years, whichcan decrease the compression work through internal evaporative cooling in compressor,increase evidently the power output of the engine, promote the thermal efficiency, and isconsidered as a cost-effective technique of relatively easy to implement. Wet compressiontechnique can also restrain NOxproduction in combustion resulting in low pollutant emission.Therefore, a comprehensive and thorough numerical investigation on wet compression withgas turbines is carried out in this dissertation.Wet compression process in compressors consists of complicated two-phase flows withphase change and the key points of this technique involve the studies of droplet motion andevaporation processes. In this study, aerodynamic secondary breakup of big moving dropletsand droplet/blade impingement in compressors are investigated. And droplet/wallimpingement theory proposed by Bai and Gossman is used to analyze droplet/bladeimpingement phenomenon resulting in four regimes as stick, rebound, spread and splash,according to droplet Weber number. Depending on the flow character in compressors, it’spredicted and demonstrated that spread and splash are the two dominant regimes whendroplet/blade impingement takes place. Based on the theoretical analysis and experimentalobservations in wet compression test on a transonic stator, one simplified breakup model isassumed to simulate droplet/blade impingement in compressors to get a more reasonablenurerical solution. Numerical and theoretical methods are used to analyze the differences ofwater film breakup after shedding from the trailing edges of fast-moving rotor and stationarystator respectively.The established model was applied to study and analyse the wet compression progress ina multistage axial compressor. And the breakup and radial moving of drplets with diversediameters injected from the mid-inlet is investigated. Based on this compressor, the study of wet compression performance of multistage compressor is carried out which involvescharacteristics of volume flowrate variation and blade load distribution.Wet compression influences not only the compression process in compressor, but also thecombustion process and emissions in combustor, and the change of mass flowrate andcompositions of the working fluid. Entire flow simulation of a small turbojet engine withwater injection from its inlet has been implemented to predict the effect of wet compressionon the performances of the full engine and its components, and the main pollutant emissionsof combustor. Under the condition of keeping the constant fuel rate with respect the inlet airflowrate, water injection with different droplet diameter results in different evaporationproportion of droplets in compressor and in combustor which evidently can influence theengine performance. Through analyzing the volume flowrate change in each blade passageand the load distribution of each blade, the effect of wet compression on flow separation incompressor is well interpreted. Last, detailed analysis of wet compression effect on the mainpollutants NO and CO in combustion is carried out, and the exponential correlation of NOproduction against evaporation rate is set up.In this study, the mechanism of droplet/blade impingement in compressor is wellinterpreted, profound understanding of some essential points in the effect of wet compressionon flow field is made, and the effect of wet compression on pollutant emission of combustoris well analyzed. All the work here can contribute a lot to the theoretical and practical studyon wet compression of gas turbines. |
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