Study Of High Pressure Ratio Centrifugal Compressor Stability Improvement By Non-Axisymmetrical Flow Control Method For Internal Combustion Engine

The demand of energy saving, reduction of CO₂emmision and powerrecovery at high altitude for an internal combustion engine pushes the boostingpressure ratio toward higher level. High boosting technology turns out to be oneof the key technologies of the advanced internal combustion engine. Stableoperation range deteriorates sharply as the pressure ratio goes up, which makesthe stability investigation as well as its enhancement a challenge in a highpressure ratio centrifugal compressor. Self-Recirculation-Casing-Treatment(SRCT) is a widely used flow control method in turbocharging compressor. Thestudy on this method bases on the control of recirculation flow rate. Theinfluence of flow distortion caused by a volute is seldom involved. Theconfiguration of SRCT is axi-symmetrical.The detailed flow distribution in the high pressure ratio centrifugalcompressor is investigated by experiment. It is discovered that a significantdistortion in the diffuser is caused by the variation of the static pressure in thevolute at off-design conditions; the distortion further influences the flowdistribution in the impeller. Furthermore, the static pressure distribution isstrongly influenced by the rotational speed.The distorted flow distribution phenomenon and its mechanism are studiedin detail. It is found that the speed-depended flow distribution results from therotating passage and the propagation of the distortion from the impeller outlet.A perturbation can be caused at the impeller outlet by the distorted staticpressure distribution nearby. Then the perturbation propagates upstream intothe passage and reaches the leading edge of main blade. As a result a distortedcircumferential distribution near impeller happens.The influence on flow condition at impeller inlet by SRCT is investigated.It is found that the flow distortion can be depressed by SRCT. The effect of thedepression is determined by the circumferential distribution of recirculationflow. Based on the study of flow field near compressor stall and influence ofSRCT, a new asymmetrical flow control method is suggested: matching themaximum recirculation mass flow rate of the circumferential distribution with the passage with the minimum static pressure in order to achieve optimizedeffect of stability enhancement.A new asymmetrical SRCT is designed based on the method and theinvestigation of SCRT geometries. Testing is carried out on a pressure ratioturbocharging centrifugal compressor. The result shows that the overall effectof stability enhancement on the compressor for the new SRCT withasymmetrical geometries is notably improved. Specifically, the surge mass flowrate at design speed is reduced by4.1%by the new SRCT compared with thesymmetrical one.