Research On Recirculation Device Retrofit Of Centrifugal Compressor

Centrifugal compressor is the core component of the turbocharger,and its stable working range has been a hot issue for people to study.The addition of recirculation device is a very effective way to improve compressor’s performance.Based on the research of the existing recirculation device,in order to pursue better performance,it is necessary to do the modification research of the recirculation device.This paper analyzes the improvement mechanism of adding recirculation device.In order to analyze the differences in the flow field structure inside the compressor of different recirculation device models,the modified compressor model are compared with the original model.Research content and conclusions are as follows:First of all,in order to investigate the improvement mechanism of the performance of the compressor with recirculation device,the centrifugal compressor with recirculation device and the centrifugal compressor without recirculation device were compared to investigate compressor’s internal flow fields.Studies have shown that after the addition of the recirculation device,the performance of the compressor has indeed improved under conditions of near stall condition and maximum efficiency condition.Due to the suction effect of the recirculation device,the pressure ratio is improved under all flow conditions,and there is no significant difference in efficiency.However,there is a slight deterioration in the performance of the compressor in the near choke condition.It was found that the changes caused by the recirculation device to the internal flow field of the compressor were mainly concentrated in the upstream flow area,with little impact on the downstream flow area.Secondly,in order to find the optimum position of the opening of the recirculation device,the rear slot of the original machine is moved up and down by 2mm in the tangential direction to obtain two retrofit models,and the three models are simulated and analyzed.When the rear slot moved downward,the compressor’s performance deteriorates under most flow conditions,while the model whose rear slot is moved upward has an obvious improvement effect on the performance of the compressor.The downward movement model shows a drop in efficiency over the full flow range.It’s pressure ratio slightly increases at near-plugging conditions,decreases at the rest of the flow range.This model’s steady operating range narrows.The upward movement model has improved the efficiency in the flow range between the near-stall flow rate and the highest efficiency point flow rate condition,the pressure ratio in the full flow range has increased,and it’ stable working range has been broadened.The effect of moving the opening position of the recirculation device is mainly concentrated near the leading edge of the main blade.The upward movement model reduces the distribution of entropy in the same area under the near stall condition and increases the static pressure value in the area.The upward movement model also improved fluid inlet velocity distribution,increasing static pressure at the highest efficiency point condition,but the entropy distribution has a certain increase.In general,the upward movement model has improved compressor’s performance over the original model,while the downward model has no improvement.Finally,in order to make the results more accurate,the upward model and the original model were selected to perform unsteady calculations under near-stall flow condition and compare them.The results of the study are basically consistent with the steady results.The efficiency of the compressor is improved and the pressure ratio is increased under near stall condition.This indicates that the upward movement of the opening of recirculation device is beneficial to the performance of the original model.This conclusion helps further research on recirculation device retrofit.