Study On Stability Extension Of Static Components In Centrifugal Compressor

Centrifugal compressor is an energy conversion device converting the mechanical energy of the motor into the pressure and kinetic energy of gas by driving the gas in the impeller passage through the rotation of impeller.The static components such as diffuser and return channel in the centrifugal compressor play an important role in improving the performance of the compressor stage and expending the range of stable operating range.The flow pattern in the static components' passage is quiet complex due to the influence from the upstream rotating impeller and the constraints of the mechanical structures to flow.Therefore,it is necessary to explore the flow mechanism of the static elements within the static components which is of great significance to the design and optimization of the mechanical structures.By using the CFD software NUMECA,the flow patterns in the static components of centrifugal compressor stage,which is one of the series of LB56150 KY108 designed by Shenyang Blower Works,are studied in this paper.The performance and stable operating conditions are improved through the aerodynamic of the mechanical structures.In the first part for the diffuser modification,the effects of vaneless region are analyzed.The length of vaneless region is modified by changing the ratio between the diffuser inlet radius and the impeller outlet radius?R₃/R₂?,and numerical simulation of six compressor stage models are carried out with different radius ratios among 1.06¹.20.The conclusions are as follows: the proper increase of vaneless region length decreases the flow separation zone at the impeller outlet near shroud,optimizes the distribution of flow angle at diffuser inlet and improves the performance of impeller,diffuser and stage.However,the excessive large vaneless region length causes great loss in flow passage and leads to the deterioration of compressor stage.In the second part for the diffuser modification,the effects of vaned diffuser casing shrinkage are studied.The original design is based on the non-shrinkage diffuser casing.The modified designs includes the narrower vaned diffuser casing whose width is only reduced from hub,and from the one only reduced from the shroud,and the one from the hub and shroud with the same reduction.The results show that both the polytropic efficiency and pressure ratio are improved,and the stable operating range is expanded by reducing the diffuser casing shrinkage.By comparing the stage performance,the design with width reduced from shroud is the best.Theshrinkage optimizes the distribution of flow angle at the inlet and outlet of vaned diffuser and decreases the separation vortex.In the part for return channel modification,several centrifugal compressor model stages under different return channel stagger angles are numerically studied.The energy gradient theory is successfully applied to study the flow pattern in return channels and the distribution of energy gradient function K is obtained for all.The results reveal that the instability easily occurs mainly in the tail and exit position of the return channel blade.The stage performance reaches best as the return channel stagger angle equals to 37° in design flow.