Research On Aerodynamic Load Characteristics Of Centrifugal Compressor Semi-open Impeller Under Small Flow Conditions

Centrifugal compressor is a kind of rotating machinery widely used in the petrochemical industry,metallurgy,aerospace and other fields.As the performance requirements for centrifugal compressors gradually increased,to obtain a higher pressure ratio,the working point of centrifugal compressors is getting closer and closer to small flow conditions.Therefore,flow instability phenomena such as rotational stall under low flow conditions have become an important factor limiting the performance improvement of centrifugal compressors.It is of great significance to study the occurrence mechanism of the rotating stall phenomenon in centrifugal compressors,determine the aerodynamic load characteristics caused to the blades when the stall occurs,and to expand the stable operating range of the compressor and improve the compressor performance.This paper takes an actual centrifugal compressor as the research object,and uses the CFD numerical simulation method to perform the unsteady calculation of the impeller and diffuser flow field under small flow conditions.The DMD modal decomposition algorithm is used to decompose and reconstruct the stall flow field,and the frequency and flow field structure corresponding to the rotating stall is extracted.Based on numerical simulation,combined with the existing conditions of the compressor test bench,the scheme design of aerodynamic load characteristic test and dynamic stress test under small flow conditions was carried out,and the accuracy of the test system was verified.The main research contents of this article are as follows:(1)Using the CFD numerical simulation method,the flow field of the centrifugal compressor under low flow conditions was analyzed,and it was determined that the rotation stall phenomenon in the flow field of the centrifugal compressor impeller and blade diffuser under low flow conditions.By analyzing the flow characteristics in the compressor flow field,the causes of the flow field stall in the impeller and vane diffusers are studied.The rotation stall in the impeller is mainly caused by the flow instability on the side of the cover disc.The lowenergy fluid flowing in the radial direction generated by the flow separation on the suction surface is mixed with the tip clearance flow,and the formed low-energy fluid mass is mixed with the mainstream near the blade leading edge Mixing,resulting in vortices at the inlet of the impeller and blocking the flow.The rotating stall phenomenon in the blade diffuser is mainly caused by the flow instability on the disk side.The impact of the airflow into the diffuser causes the annular vortex separation phenomenon on the suction surface of the diffuser blade,and a recirculation zone is formed on the disc side.The diffuser outlet moves to form a vortex in the area between the diffuser and the impeller.The accumulation of the vortex blocks the flow in the diffuser,which eventually causes a rotational stall in the blade diffuser.(2)Based on the flow field data obtained by the simulation of unsteady constant values,using the DMD method to decompose and reconstruct the pressure field on the impeller blade,the aerodynamic load frequency caused by the rotating stall on the impeller blade is obtained,and through the pressure field reconstruction,it intuitively shows that the pressure load caused by rotating stall on the impeller blade.The stall frequency in the impeller and blade diffuser was identified,and the frequency of aerodynamic load caused by the rotating stall on the impeller blade surface was obtained.By reconstructing the modal flow field corresponding to the rotating stall,the unstable flow structure in the flow field of the impeller and blade diffuser is intuitively presented,and the phenomenon of rotating stall is clearly shown in the impeller and blade diffuser The process of circumferential propagation.(3)Based on the analysis of the flow characteristics of the centrifugal compressor under low flow conditions,combined with the existing conditions of the test bench,aerodynamic load characteristic test plan and dynamic stress test plan were formulated.The wireless strain collection equipment was customized,and its reliability was verified by testing the strain of the beam structure.