Aerodynamic Design And Matching Of Air Cycle Machine With Air Foil Bearings

Air cycle machine is a key component of airplane environmental control system.Mostly,it is a micro turbine with gas foil bearings.This kind of turbine has the characteristics of high pressure ratio and high speed.Many literature deals with the design and simulation of turbine with high pressure ratio.However,it only analyzes the flow performance of the impeller and lacks the simulation research on the whole machine.When the pressure ratio is relatively high,a transonic nozzle design is needed.The selecting of the throat position in the transonic nozzle design is of great importance,but no quantitative conclusion has been drawn.This article will focus on these issues.This paper introduces the research status of gas foil bearing technology,centrifugal compressor design,centripetal turbine design,transonic nozzle design and turbo matching study at home and abroad.Through literature research,the accuracy of the numerical simulation method in this paper is verified.Through the research on the aerodynamic design and matching of ACM,the following conclusions are drawn:(1)In the CFD calculation,grid independence verification is performed.For the compressor wheel,turbine wheel and turbine machine in this paper,to ensure that the change in the efficiency which caused by the number of grids is less than 1%,the number of grids needed is 420,000,630,000 and 2.8 million respectively.(2)For the centripetal turbine whose pressure ratio reach 8 in this paper,a design scheme with a reaction ratio of 0.41 and a characteristic ratio of 0.66 was chosen.The gas foil bearing was designed and selected.The selected bearing has a detachment speed of 20165 rpm,and the bearing capacity is 6.5N,which meets the requirements.(3)The design of the micro-transonic nozzles was assisted by the CFD method.The optimum nozzle blade angle was determined to be 17 degrees.In order to investigate the influence of the length of the cylindrical section of the throat on the flow of the nozzle,eight different nozzles were designed.The ratio of the length of the cylindrical section of the best nozzle throat to the diameter of the throat is 3.45.(4)Compared with the aerodynamic simulation of the complete impeller and turbine expander,under the same inlet and outlet conditions,the efficiency of the individual impeller is 92.96%,and the efficiency of the turbine machine is 87.46%,but the flow in the whole machine is more evenly.(5)In this paper,the output power of the turbine is 43027 W,and the power consumption of the compressor is 38158 W.The flow and speed of the two compressors are equal.The matching requirements were meet.In variable conditions,the compressor has a large surge margin.