Study On The Analysis Method For Leakage Flow And The Vortexes In Unshroud Centrifugal Impellers

The unshroud centrifugal impeller is the core component of some power equipments in the aviation and petrochemical industry.Analyzing the flow characteristics of the impellers has gradually become the focus of many researchers recently,for that the right analysis method is helpful in understanding the flow mechanism which can provide references for loss suppression.In order to reveal the reasons for tip leakage flow and the development of vortexes in the impellers,the analysis method of the flow characteristics has been developed on the base of simulation,and the new method is applied to analyze the flow of a typical impeller successfully.Aiming at the factors related to the tip leakage flow,the check of numerical method and the application of the quantitative methods proposed by former people are finished at first,and then by calculating the scrapping ratio and applying the partial least square method,results can be given as follows: after discussing the distribution characteristics of the parameters related to leakage flow and the result of velocity,it can be determined that the driving mechanisms are tip load and scrapping pressure;the value of scrapping ratio decreases along the streamline of the blade,which indicates that the effect of shroud scrapping on leakage flow increases along the streamline direction;in terms of the regression coefficient and the variable importance projection,the calculating results of tip load are a little bigger than scrapping pressure's results,which indicates that tip load is much more important in promoting leakage flow than scrapping pressure,but the influence of scrapping pressure on leakage flow cannot be ignored.In order to identify the vortexes,based on the existing helicity method and the eigenvalue method,a combined vortex identification method has been proposed.With the application of the method,it could be found: from the inlet to the outlet of the impeller,the vortex shape turns to be full,and the vortexes stretch from the shroud side to the hub side;seen from the streamline direction,except for the passage vortex near the trailing edge,the other vortexes are anti-clockwise;after testing and analyzing the identification result of the vortexes,the vortexes can be classified into leakage vortex,passage vortex and wake vortex: the leakage vortex is located in the first half of the impeller,and it is caused by the leakage flow;the passage vortex is located in the second half of the flow passage,and it is caused by the secondary flow driven by the leakage flow as well as the reversed flow of the shroud;the wake vortex is generated by the coupling effect of secondary flow and the leakage flow.The partial least square method and the combined vortex identification method are introduced in analyzing the flow characteristics of unshroud centrifugal impellers,and finally,the quantitative relationship between the leakage flow and its influence factors,the effects of tip load and shroud scrapping on leakage flow,as well as the distribution and rotate direction of the vortexes are identified.Research here can provide references for the design and flow mechanism analysis of centrifugal impellers.