| The flow parameters of centrifugal impeller exit are characterized by high speed and strong nonuniformity along the spanwise in a highly loaded centrifugal compressor,which make the inflow conditions of diffuser at downstream is non-uniform along the spanwise and transonic.Because of it,the flow structure of diffuser is complex and the performance is weaker,and it restrict seriously the development of the high performance and high pressure ratio centrifugal compressor.In order to clearly understand the influence of the non-uniform flow of impeller exit on the internal flow structure of diffuser,the performance and flow structure of the diffuser with the non-uniform inflow along the spanwise about velocity and angle is studied in this paper,and the design method of the twisted type vaned diffuser is explored.The main research work of this paper includes:1.The study of developing laws of the performance and flow structure for transonic vaned diffuser,and the analysis of its flow mechanismThe performance and flow mechanism of the vaned diffuser were studied through the calculation and analysis of internal flow fields with a series of inflow Mach numbers ranged from 0.7 to 1.2.It was found that the flow speed first increased to supersonic in the partial high-speed region,which was formed in the vanless extension with highly subsonic inflow,with the increase of inflow speed.And then shock waves were formed graduall,and its intensity increased as the inflow velocity increases.With the increase of pressure gradient of suction surface following the intensity of shock waves,the boundary layer thickened,and finally the separation vortex was formed on the trailing edge.2.Research the influence of the non-uniform velocity inflow along spanwise on the performance and flow structure for diffuser,and analysis the flow mechanismThrough the calculation and analysis of the performance and flow structure for vaned diffusers with uniform and non-uniform inflow conditions,this paper studied the influence of non-uniform inflow on them and the formation mechanism.It was found that the boundary layer thicken rapidly around the blade on the side of hub when the inflow was non-uniform,because of the higher pressure gradient of the low speed inflow layer than which with uniform inflow.The separation vortex was formed on the pressure surface,and part airflow in the main stream region was involved,which resulted the performance weaker with great flow losses and flow channel blocking.3.Research the influence of the non-uniform angle inflow along spanwise on the performance and flow structure for diffuser,and analysis the flow mechanismThe influence of non-uniform angle inflow on the performance and flow structure for vaned diffusers was researched through the calculation and analysis of internal flow field with uniform and non-uniform inflow conditions.Because of the pressure gradient along spanwise,strong threedimensional flow occurred in the vaned diffuser when inflow was non-uniform,and it resulted some flow losses.Because of negative incidence inflow on the side of hub,the pressure distribution of suction surface was greater than which with uniform inflow,causing the flow separation occurred on trailing edge,which made the performance weaker with large flow loss.4.Explore the design method of twisted type vaned diffuser which would adapt to non-uniform angle inflow along the spanwise,and analysis the mechanism of performance improvementThe twisted type vaned diffuser was designed according to the inflow angle,and then the internal flow fields of the twisted vaned diffuser with different stacking modes were calculated and analysed.It was found that the separation vortices were disappeared because of the significantly ameliorated pressure distribution for twisted type blades,which improved the performance of vaned diffuser with smaller flow loss. |
PDF Full Text Request