Development And Application Of Aerodynamic Design Program For Centrifugal Compressors

Turbomachinery has already become a mainstay in our national economy. Its performance affects power consumption and machine running safety directly. The demands on the centrifugal compressors with higher efficiency and total pressure ratio are increasing. For example, military UAV (Unmanned Aerial Vehicle) employs centrifugal compressors with high pressure ratio. Those centrifugal compressors with high efficiency and excellent stability are needed in process industry. Moreover, foreign multistage centrifugal compressor products applied in the air-conditioning and natural gas transportation fields take the main share of China market. Therefore, the effective solution is to develop aerodynamic design program for centrifugal compressors including different flow coefficient type. Through this process, key design technologies can be accumulated and served for the corresponding application areas.Aerodynamic design program for centrifugal compressors was developed based on empirical loss models and calibrated by three centrifugal compressors having experimental and numerical simulation data. Then, four single stage centrifugal compressors with different inlet flow coefficient were designed for specific projects by means of the self-developed design program. One of the four centrifugal compressors has been manufactured and will be tested by a coorperative company to confirm its performance.A low flow coefficient centrifugal compressor was developed as the last stage of a multistage compressor. The flow medium was natural gas. The design goal was to achieve higher efficiency. According to the requirements of a solar dish-brayton system, a centrifugal compressor stage with a minimum total pressure ratio of5, an adiabatic efficiency above75%and a surge margin more than12%needs to be designed. A single stage, which consists of impeller, radial vaned diffuser,90°crossover and two rows of axial stators, has been designed to satisfy the requirement of the solar dish-brayton system. To achieve the specific stage performance, an impeller with a6:1total pressure ratio and an adiabatic efficiency of90%was designed and its preliminary geometry came from an in-house one-dimensional program. Radial vaned diffuser was applied downstream of the impeller. Two rows of axial stators after90°crossover were added to guide the flow into axial direction. This centrifugal compressor belonged to medium flow coefficient type. A centrifugal compressor with high inlet flow coefficient of0.2, having a narrow operating range and unstable running situation even at design speed during the test, was investigated. To better reveal flow details in this centrifugal compressor, numerical simulations have been carried out and indicate that excessive impeller flow diffusion results in the poor performance of this centrifugal compressor. For the same inlet flow coefficient, six redesign cases coming from an in-house one-dimensional analysis program were proposed together with impeller trimming and equal flow area design method for corresponding vaneless diffuser. Finally, a suitable redesign case was selected and analyzed.Based on the accumulated design technology regarding different coefficient centrifugal compressors, a multistage centrifugal compressor with the total pressure ratio of12was designed, which would either verify the performance of developed design system or satisfy the need of a project. This multistage centrifugal compressor employed a single shaft, back-to-back structure layout. An intercooler was added between the fifth stage and the sixth stage. The numerical simulation indicated that the performances of this multistage centrifugal compressor were satisfactory. During the design process, related key design technologies were also accumulated.The flow situation between impeller exit and diffuser inlet was thought to be critical to the aerodynamic performance and stability of centrifugal compressors. To investigate the stall improvement mechanism of vaneless diffuser flow path control, a centrifugal compressor is simulated and compared with existing experimental data. According to characteristics of flow field and stall mechanism, a convergent-divergent type of impeller-diffuser casing was designed and analyzed. The result showed that the stable flow range of centrifugal compressor increased by2.8%, however, no obvious positive effects were found on the adiabatic efficiency, which was slightly lower than that of prototype.