Study And Improvement Of Aerodynamics Of The Return Channel Of A Centrifugal Compressor With Large Flow Coefficient

Centrifugal compressor is a kind of machine which improves the pressure by rotating blade. Is widely used in various sectors of the national economy. With the development of science and technology, the performance of the centrifugal compressor is gradually increasing, and the international competition tends to become more and more intense. Therefore, designers are required to design a high pressure ratio, high flow, high efficiency multi-stage centrifugal compressor.Centrifugal compressor is composed with the rotor and the stator parts. In the early design process, centrifugal compressor designers pay more attention to the research and development of the compressor impeller, the attention of the stationary part, especially the reflux device is lower. However, During configuration process of large flow multi-stage compressor of 0.2 Flow coefficient, the researchers found that the first stage of the compressor exit flow field is not uniform, This causes the flow turn bad and efficiency decreased in the next stage. Therefore, improving the uniformity of the flow field of the first stage is one of the ways to improve the efficiency of the centrifugal compressor.In this paper, the flow field of the first stage return is analyzed, in order to find out the cause of the uneven flow field of the first stage. Through the analysis of the flow field, the flow field of return inlet is very uneven, the air flow angle are different at different locations. In the return channel, the strong second flow vortex is generated, this makes the circumferential velocity distribution of the exit cross section is not uniform. In the next stage, the inlet condition of the impeller is deteriorated, and the efficiency is greatly reduced.In order to determine the influence of the inlet flow on the uniformity of the outlet flow field, the inlet condition of the return is changed into uniform air intake, and the first stage return and the next stage are calculated by CFD. The results show that, under uniform intake conditions, the second flow vortex in the return channel is disappear, the flow field uniformity of the first stage outlet is improved significantly, and the efficiency of the second stage is significantly improved.According to the characteristics of the flow field, three schemes are adopted to modify the vane of the return. Scheme one:According to the angle of the flow, modify the distribution of installation angle of the return inlet. But the results show that the change of the return inlet angle did not improve the uniformity of flow field. Scheme two:According to the distribution of the return outlet flow angle, to reduce the blade angle of the wheel and the wheel cover, to improve the blade angle of the middle section. The stage outlet flow field is improved in this section, but there's still a lot of room for improvement. Scheme three:On the basis of the scheme two, the return blade is extended to the middle part of the curve. The numerical simulation results show that the uniformity of the first stage outlet flow field is significantly improved. The second stage efficiency is improved by 1.7%, and the whole stages efficiency is improved by 0.7%. To calculate the variable condition of section three, performance curve was significantly improved. At the 90% point, the efficiency is improved by 2.2%.The results show that the uniformity of the flow field in the first stage outlet is improved by the modification of the vane of the return, which makes the efficiency of the whole stage improved obviously, the small flow rate is especially obvious.