Research On Performance Of Centrifugal Compressor Based On Nonlinear Harmonic Method

Micro centrifugal compressor has been widely used for a time because of its small size,light weight,simple structure,relatively easy manufacture,high single stage pressure ratio and high reliability.At present,the requirement of high pressure ratio of compressor is getting higher and higher in aviation field,and the study of internal flow pattern of compressor is mainly numerical simulation,so it is very important to carry out numerical simulation of centrifugal compressor.Many complex unsteady factors interact in centrifugal compressor,and the unsteady effect is very obvious.In order to better predict the complex unsteady effect between blades,a new unsteady simulation method,non-linear harmonic balance method,has been developed.This method combines the high accuracy of steady calculation and the fast speed of unsteady calculation.Because of its advantages,the research on this method has been paid more and more attention.In this paper,the NUMECA software is used to simulate the centrifugal compressor of a micro gas turbine at five different speeds(100%,90%,80%,70%,50%)and draw the characteristic curve of the centrifugal compressor.The flow field distribution of the centrifugal compressor under the design condition is studied.Secondly,the flow field of the centrifugal compressor under three typical operating conditions(blocking,design and stall)at three rotating speeds(100%,80% and 50%)was analyzed,and the similarities and differences of the internal flow field of the centrifugal compressor at different rotating speeds were compared.The results show that the shock wave occurs at the leading edge of the main blade of the centrifugal compressor,and the workflow range decreases obviously with the decrease of the rotational speed.Low rotational speed will lead to the decrease of the compressor's turbocharging capacity and efficiency.On this basis,a new unsteady simulation method,Nonlinear Harmonic Balance Method(NLH),is used to simulate the above five rotating speeds.The characteristic curves of NLH method are drawn and compared with the steady calculation results.The unsteady difference of internal flow field is analyzed.The near-maximum efficiency point in the calculation of the nonlinear harmonic method is selected to analyze the flow field structure in the compressor in detail.The development of tip clearance flow and impeller outlet wake are studied.The interaction between impeller and diffuser in centrifugal com-pressor is also studied.The results show that near the stable operating range of the compressor,the non-linear harmonic balance method is basically consistent with the steady calculation results,and there is a slight difference between the near stall appendages.The interference between impeller and diffuser in high pressure centrifugal compressor will lead to strong unsteady phenomena.