Research And Analysis On The Performance Of Tandem Axial Diffuser For Micro Turbojet Engine

Due to the limitation of compact structure,the flow in the axial diffuser of the micro turbojet engine centrifugal compressor is poor,which has a great impact on the performance of the micro centrifugal compressor.Therefore,in this paper,the centrifugal compressor of a micro turbojet engine is taken as the research object,and the axial diffuser part of the compressor is modified in tandem.The internal flow field is analyzed with the commercial software NUMECA,and the influence of several main geometric parameters of the tandem axial diffuser on the performance of the micro centrifugal compressor is studied.The main research contents and conclusions are as follows:In this paper,the relevant theories of NUMECA software used are described,and the software tools are calibrated with examples with experimental results to ensure the reliability of simulation results.The flow of various components of a centrifugal compressor for a micro turbojet engine under different design conditions is studied in detail by using numerical calculation method.It is accurately pointed out that the energy loss of a single row of blade axial diffusers is concentrated at the hub side of the diffuser and the middle position of the blade,and the main reason for the energy loss of the axial diffuser is explained.Three typical geometric parameters,chord length ratio,circumferential position and axial spacing,are further selected to calculate and analyze their effects on the performance and flow conditions of tandem axial diffusers using numerical simulation tools.The research on chord length ratio shows that the change of chord length ratio has little influence on the flow separation of the front row blades,while the influence on the separation of the rear row blades at different heights is different.In this study,the best effect can be obtained by taking a larger chord length ratio(such as 1.50 or2.33).The research on circumferential spacing shows that the effect of the rear row blade close to the front row pressure surface is relatively good,which can not only inhibit the separation of the front and rear row blades at the same time,but also help the front row blade wake to continue to deflect.The comparative study of axial spacing shows that the effect of 0 axial spacing is better than that of positive axial spacing,and the positive axial spacing is easy to cause separation near the leading edge of the rear row blades,resulting in greater flow loss.Through comprehensive analysis of the flow field of each model,it is found that the front row blades affect the work of the rear row blades through the way of the wake passing through the rear row blades,and the rear row blades affect the front row blades through the suction action of the suction surface near the trailing edge of the front row blades.The chord length ratio,circumferential position and axial spacing shall be selected so that the suction surface of the rear row blades is close to the front row trailing edge to fully exert the suction effect,and avoid the rear row blades being covered by the front row wake,so as to obtain the best effect.In addition,the opening direction of the gap between the front and rear rows of blades shall be tangent to the rear row of blades to avoid flow separation of the rear row of blades.