Design And Study On The Second Stage Of The 4MW Gas Turbine Centrifugal Compressor

As the typical distributed energy power plant,micro and small gas turbine have a great application prospect.For the advantages of high pressure ratio and compact structure,the centrifugal compressor is widely used in these kinds of gas turbines.Therefore,the design and research of centrifugal compressor is very important for the development of micro and small gas turbine.In this thesis,the second stage centrifugal compressor of a 4MW industrial gas turbine is designed and studied.First of all,the Concepts NREC software is used to finish the designation of the impeller and vaned diffuser.The impeller axial dimension is limited as required,and the diffuser is designed from single row to double rows.The NUMECA software is used to compute the design model,then adjust relevant parameters with the computation results to obtain the optimal design scheme.Subsequently,some studies are done with the designed impeller,such as the influence of the tip clearance,splitter blade length and splitter blade circumferential position distribution.The results are as follows:(1)The performance of the impeller is basically proportional to the tip clearance.The smaller clearance can effectively inhibit the negative effects of clearance flow on the internal flow of the impeller and reduce the gas flow through the blade tip.In addition,the influence area of clearance is mainly distributed in the latter half of impeller flow path.(2)Through the ANSYS finite element analysis,the recommended clearance value is 0.3mm.(3)Splitter blade may cause adverse effects on the flow field if it is too long or too short.Study shows that there is an optimal value which can balance the impeller performance and stability.For this impeller,when the length of chamber line in the splitter blade divide the length of the chamber line in the main blade is 0.63,the impeller has the best performance.(4)The circumferential position of splitter blade can change the flow conditions of two channels and influence the distribution of tip clearance flow.Impeller has the best performance when the splitter blade is located on the middle of the adjacent main blade.Meanwhile,the flow field is worse when the splitter blade is biased towards the suction surface than when the pressure surface is biased.Finally,the influence of the circumferential position of the tandem cascade diffuser on the performance of the compressor is studied.The six sets of evenly distributed angles are selected in the rear row of the tandem cascades,which are respectively recorded as the position 1 to the position 6.Then,the six schemes are numerically calculated and compared with the single-row diffuser.The result shows that the tandem cascade has higher performance,stability,higher static pressure recovery coefficient and uniform outlet velocity distribution than the single-row diffuser.In addition,for the tandem cascade,different positions at the second row have different outlet radial velocity and flow angle distribution,and can change the influence of the separation from the first row.Through the analysis,compressor has the best performance when the leading edge of the second-row blade is about 1/3 pitch from the pressure surface of the first-row blade.