Investigation On Flow Characteristic And Performance Of Highly Loaded Partial Admission Turbine

As one of the core components in defense and civil power plants,more compact structure,fewer stages,lighter weight and higher efficiency turbines are constantly being developed and this makes the turbine work under highly loaded and transonic conditions.Furthermore,partial admission makes blade rows after the admission arcs work in non-uniform circumferential inflow condition,and the internal flow condition of the blade row is more complicated,and the rotor blades of various stages are also subjected to more intense excitation forces.Therefore,conducting a systematic study of the optimal design method of highly loaded turbine under partial admission,clarifying the unsteady flow loss mechanisms and excitation characteristics of partial admission,and finding out better flow organization methods and structural configuration of partial admission turbine are of important significant for these application fields.Partial admission is usually used for turbines with the characteristics of low air consumption,highly loaded,and low aspect ratio,which can reduce the secondary loss and the processing difficulty of fairly small blade height.In addition,the structural form of partial admission is also used in the control stage of steam turbine with nozzle control governing,which can reduce the throttling loss during steam distribution and improve the part load efficiency of the unit.The optimal design of partial admission turbine is studied firstly in this thesis.MATLAB is applied to carry out secondary development of existing software modules,realize data transmission between each module and establish step-by-step optimization design platform for two stages partial admission turbine under full admission single passage and partial admission environment.Basing on the approximate model obtained by neural network training which reflect the mapping relationship between the optimization parameters and the aerodynamic performance of the turbine for each optimization process and the global optimization of the particle swarm-genetic hybrid algorithm,the optimal result for each optimization process is obtained.During the optimization process of OPT STEP1 and OPT STEP2,the influence of reaction degree on the leakage loss after partial admission construction is taken into consideration,with the optimization of in/out blade angles and stagger angles of each blade row and the stacking law of first stage rotor,the internal flow state is improved and the total to static efficiency is cumulatively increased by 3.24%.Then,the optimized full admission single passage model single-OPT2 was constructed to partial admission model PA-OPT1 and its total to static efficiency is increased by 3.24%compared to PA-ORI.After that,the blade profile of first stage rotor was then optimized under partial admission environment,the flow separation caused by circumferential non-uniform aerodynamic parameters distribution under partial admission condition is eliminated,and the flow moving in the circumferential direction is decreased by 10.30%compared to PA-OPT1.Overall,the total to static efficiency of optimized partial admission turbine PA-OPT2 is 0.85%higher than that of PA-OPT1 and a cumulative increase of 3.72%compared to the prototype PA-ORI.On this basis,the numerical study of the unsteady flow characteristics of partial admission turbines with different structural types is carried out.For the case3 scheme whose second stator blade row is also constructed with partial admission,its static pressure level corresponding to the rotor 1 region behind the non-admission arcs is higher and the pressure difference between this region and rotor 1 region behind admission arcs is smaller than case2 scheme which decreases the mixing degree of circumferential flow due to partial admission,and the time averaged energy loss coefficient of rotor 1 is smaller.At the same time,the flow from the front stage is collected and integrated through the second stage partial admission stator passage,and then enters the second rotor to do work which makes the flow condition in the second stator passage of case3 scheme is closer to the ideal state of full admission casel scheme and the second rotor blades behind these stator passages are also working under higher efficiency state than case2 scheme.Compared with case2 scheme,the time averaged total to total efficiency of first stage,total to static efficiency of second stage and overall total to static efficiency of the two stages are increased by 3.14%,8.63%and 4.13%for case3 scheme respectively.However,for case3 scheme,without fully mixing and homogenizing of the flow from front stage through full admission second stator blade row as case2 scheme,the second rotor blades of case3 are subjected to more intense excitation forces,the maximum alternating stress value acting on case3 second rotor blades increase by 32.58%compared with case2.The clocking position of stator rows has a significant effect on the loss of both second rotor and stator under partial admission condition.The time averaged energy loss coefficient of second stator for the optimum clocking position scheme PA 3.0 increases by 5.12%compared to the worst scheme PA₀.0,and the time averaged energy loss coefficient of second rotor for PA₃.0 decreases by 7.49%compared to PA₀.0.The time averaged total to static and total to total efficiency of optimum clocking position scheme PA 3.0 increases by 1.35%and 1.16%respectively compared to the worst scheme.Then,under the condition of low admission degree,the structural forms of single/double inlet re-entry turbines are designed.It is found that double inlet re-entry turbine can gain higher efficiency with more compact structure.The performance of re-entry turbine can be dramatically improved by the reduction of circumferential distance between two admission arcs,the reasonable adjustment of the stator blades in re-entry arcs and the appropriate choice of re-entry times.Re-entry turbine can maintain higher efficiency in wider speed range and under low expansion ratio conditions compared to the two stages partial admission turbine.Finally,in order to carry out the testing study of the partial admission turbine at a later stage,the selection method of the turbine simulation test parameters is expounded.The overall structure of the partial admission test piece,the design scheme of each part of the test piece,the measurement scheme and the manufacture scheme for the key components of the test piece are introduced.