Design And Optimization Of Mixed-flow Compressor And Cross-over Diffuser For Micro Turbojet Engine

With the rapid development of aviation technology,micro-turbojet engine will adopts mixed-flow compressor under the development trend of miniaturization,low cost and high performance.The mixed-flow compressor has the advantages of single-stage centrifugal compressor and multi-stage axial flow compressor.It can not only achieve higher pressure ratio and larger flow under the limited size,but also reduce the cost,and receive more and more attention.But,the mixed-flow compressor must have a matching diffuser to work.Therefore,this paper starts from the practical application of relative blank 100 kg thrust micro-type turbojet engine,the designs of mixed-flow compressor and cross-over diffuser were completed.Finally,the orthogonal optimization and the neural network optimization are completed.The core content of this article are as follows:(1)According to the aero-engine design manual,complete the design and flow field analysis of mixed-flow compressor.Select the inlet hub diameter,impeller exit inclination,axial length,blade thickness,blade tip,and blade sweep angle.Finally,the effect of the length of the compressor is investigated by different radius ratios;(2)Select various parameters to complete the design of cross-over diffuser.Then match mixed-flow compressor for combination simulation.The air-flow is analyzed to provide the direction for the subsequent optimization;(3)The mixed-flow compressor and cross-over diffuser were optimized with efficiency and pressure ratio as the optimization goal by orthogonal experiment.Compared with the original compressor and cross-over diffuser,results with efficiency as the optimization goal is more significant,efficiency is improved by3.69%,pressure ratio increased by 2.4%.Therefore,the orthogonal optimization is effective;(4)Last,the optimization work of the neural network is carried out.A sample library was established to generated 70 sets of sample points.Then the mapping relationships between inputs and outputs are obtained by the BP algorithm,the optimization by genetic algorithm.To achieve the purpose of improving the efficiency and pressure ratio.Compared to before optimization,the efficiency increased by3.77%,and the pressure ratio increased by 7.5%.After orthogonal optimization and neural network optimization,the mixed-flow compressor and the cross-over diffuser were obtained.The pressure ratio is 5.062,efficiency is 84.37% and the flow rate is 1.50 kg/s.Besides,size of diffuser is not more than 244 mm.Therefore,they can be used as the core power components of 100 kg thrust micro-type turbojet engine.