Internal Flow Field Analysis And Redesign Of Micro Centrifugal Compressor

With the development of modern aviation technology, micro aircrafts are widely applied in modern military and civil field, in the near future, micro aircrafts will play a more and more important role in various fields. The micro engine is the heart of the micro aircraft, compressor part is one of the most important parts of the engine, therefore, designed a smaller, high-pressure ratio, high-efficiency, high-performance compressor is one of the focus of the advanced aircraft manufacture. Due to compressor size limitation, for high precision manufacture is difficult, centrifugal compressor is more appropriate. Besides, centrifugal compressor single stage pressure ratio is much higher than the axial flow compressor. The flow field of the centrifugal compressor is much more complicated than the axial one, it has to control the internal flow, at the same time,consider the shock loss and the boundary flow separation, to manufacture a high-pressure and high-efficiency compressor. Design a high performance centrifugal compressor has a great value.The micro centrifugal compressor was applied to a 16 da N thrust of a micro turbojet engine, it required a centrifugal compressor modification to make it be able to achieve 20 da N thrust turbojet engine’s requirement, and the new compressor must meet the several perfomance indicators. According to the blade geometry and flow passage of prototype engine, using three-dimensional software UG to establish the engine model, and using the computational fluid dynamics(CFD) software CFX to compute the flow field of the prototype centrifugal compressor, the internal flow field data and the general performance characteristic at the design point could be obtained, then it could be compared to the test parameter. The paper was focusing on the reasons of the severe losses and why the flow field became more and more complex, which include wake, second flow, separation flow, and so on. Then, for the prototype, redesigned the centrifugal compressor to improve the perfomance, changed the flow direction so as to avoid the severe separation flow, improved the pressure ratio, efficiency and mass flow without changing the size of compressor inlet and outlet. Addition, due to the severe flow loss by the geometry of diffuser, it was difficult to control the flow due, so the blade geometry and its distribution had been redesigned. After the redesign, the new compressor flow field was recalculate d, at last, the paper had analysised the performance of the prototype and redesigned compressor.The final results showed that, after the redesign of compressor, the isentropic efficiency reached 74.36%, the mass flow was 0.4236kg/s, and the total pressure ratio reached 4.136, the three performance data respectively increased by 12.67%, 9.17% and 18.17% compared to the prototype, they all had reached the design specification. The rotate speed of the compressor was 125000r/min, the high speed resulted in supersonic speed at the tip blade position. Under the action of centrifugal force and ram compressed, the supercharging abilities of centrifugal compressor had increased. In addition, the parameters at the compressor outlet became more evenly after modification, the exit angle at the tip decreased greatly, overall, the uniformity had improved with the exit angle decreased.