Previously the features of circumferential propagation of self-induced tip leakage flow unsteadiness for a low speed isolated axial compressor rotor in the authors' laboratory were discovered and investigated via ...Previously the features of circumferential propagation of self-induced tip leakage flow unsteadiness for a low speed isolated axial compressor rotor in the authors' laboratory were discovered and investigated via numerical simulation,which only occurs below a critical stable flow point that is close to but not yet at the stall limit.Further in this paper,the detailed investigation on evolution of tip leakage flow during the throttling process into spike rotating stall was conducted by adopting the valve-throttling model.During this process,the development of the circumferential propagation of tip leakage flow unsteadiness was especially focused on.According to the unsteady characteristics of pressure signals,the evolvement of compressor flow field can be classified into four stages.As compressor throttled,the oscillation frequency of self-induced unsteady tip leakage flow decreased gradually,and thus resulted in the decrease of its circumferential propagation speed.The circumferential propagation of self-induced tip leakage flow unsteadiness is closely related with rotating instability.When the forward spillage of tip leakage flow at the leading edge occurred,the spike type rotating stall was initiated.Its flow struc-tures were given in the paper.展开更多
To get an insight into the occurrence and the mechanism of flow unsteadiness in the tip region of centrifugal compressor impellers, the flow in Krain’s impeller is investigated by using both steady and unsteady RAN...To get an insight into the occurrence and the mechanism of flow unsteadiness in the tip region of centrifugal compressor impellers, the flow in Krain’s impeller is investigated by using both steady and unsteady RANS solver techniques. It is found that the flow unsteadiness on the pressure side is much stronger than that on the suction side. The periodical frequency of the unsteady flow is around half of the blade passing frequency. The originating mechanism of the flow unsteadiness is illustrated with the time-dependent tip leakage flow and blade loading at the tip region. Due to the blockage caused by the joint effects of broken-downed tip leakage vortex, separated fluids and tip leakage flow at downstream, a low pressure region is formed on the pressure side, consequently the blade loadings is altered. In turn, the changed blade loadings will alter the intensity of tip leakage flow. Such alternative behavior finally results in the periodic process. By comparing the calculated flow field in the cases of single-passage and four-passage models, it is confirmed that the investigated flow unsteadiness is confined in each single passage, as no phase differences are found in the model of four passages. This is different from the situation in axial compressor when the rotating instability is encountered. The flow unsteadiness only occurs at the working conditions with small mass flow rates, and the oscillation intensity will be enhanced with the decrease of mass flow rate. When the mass flow rate is too small, the flow unsteadiness in a single passage may trigger rotating stall, as the disturbance propagates in the circumferential direction.展开更多
基金supported by the National Natural Science Foundation of China with project No. 50906080the National Basic Research Program of China numbered 2007CB210104
文摘Previously the features of circumferential propagation of self-induced tip leakage flow unsteadiness for a low speed isolated axial compressor rotor in the authors' laboratory were discovered and investigated via numerical simulation,which only occurs below a critical stable flow point that is close to but not yet at the stall limit.Further in this paper,the detailed investigation on evolution of tip leakage flow during the throttling process into spike rotating stall was conducted by adopting the valve-throttling model.During this process,the development of the circumferential propagation of tip leakage flow unsteadiness was especially focused on.According to the unsteady characteristics of pressure signals,the evolvement of compressor flow field can be classified into four stages.As compressor throttled,the oscillation frequency of self-induced unsteady tip leakage flow decreased gradually,and thus resulted in the decrease of its circumferential propagation speed.The circumferential propagation of self-induced tip leakage flow unsteadiness is closely related with rotating instability.When the forward spillage of tip leakage flow at the leading edge occurred,the spike type rotating stall was initiated.Its flow struc-tures were given in the paper.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51236006, 51576153)
文摘To get an insight into the occurrence and the mechanism of flow unsteadiness in the tip region of centrifugal compressor impellers, the flow in Krain’s impeller is investigated by using both steady and unsteady RANS solver techniques. It is found that the flow unsteadiness on the pressure side is much stronger than that on the suction side. The periodical frequency of the unsteady flow is around half of the blade passing frequency. The originating mechanism of the flow unsteadiness is illustrated with the time-dependent tip leakage flow and blade loading at the tip region. Due to the blockage caused by the joint effects of broken-downed tip leakage vortex, separated fluids and tip leakage flow at downstream, a low pressure region is formed on the pressure side, consequently the blade loadings is altered. In turn, the changed blade loadings will alter the intensity of tip leakage flow. Such alternative behavior finally results in the periodic process. By comparing the calculated flow field in the cases of single-passage and four-passage models, it is confirmed that the investigated flow unsteadiness is confined in each single passage, as no phase differences are found in the model of four passages. This is different from the situation in axial compressor when the rotating instability is encountered. The flow unsteadiness only occurs at the working conditions with small mass flow rates, and the oscillation intensity will be enhanced with the decrease of mass flow rate. When the mass flow rate is too small, the flow unsteadiness in a single passage may trigger rotating stall, as the disturbance propagates in the circumferential direction.
