This paper presents experimental investigation conducted on a 2-stage low speed axial research compressor with cantilevered stator vanes. Flow fields at four different axial locations in the radial stacking and bowed stator passage were measured at maximum flow point and near stall point using 4 five-hole pressure probes. The aim of the work is to study the effects of the bowed stators with hub clearance on the flow field of compressor blade passage. The investigations were conducted with the first stage of the compressor. The hub clearances of both original and bowed stators are 1.1% of span. The results show that the scale of the separation vortex, the hub leakage vortex and the lower passage vortex in the bowed blade passage becomes much smaller and the hub leakage vortex is closer to the suction side at near stall point, which causes a much smaller mixing loss in the blade passage.
Rotating stall is one of the unsteady phenomena in multistage axial compressors that will damage both of performance and service life of aero engines. Stall inception is a dynamic process including appearance of pre-stall disturbance, evolvement of disturbances into stall cells, and development of stall cells. The main purpose in researching stall inception is to reveal the origins of disturbances and stall cells, investigate the effects of aerodynamic design variations on stall inception, and find the effective ways to prevent engines from turning into rotating stall or surge. Numerical simulation is an economic, reliable and rapid tool to study stall inception. As stall inception is three-dimensional and unsteady, numerical simulation should be capable of describing these aspects. In this paper, a three dimensional unsteady computational model based on the three-dimensional unsteady Euler equations and the three dimensional multi actuator-disks model has been developed. The computational domain can be divided into two kinds. One is blade-free regions, which consist of upstream duct, the axial gaps among blade rows, and downstream duct. The other one is blade rows. The flows in blade-free regions considered inviscid, unsteady, and can be resolved using three-dimensional unsteady Euler equations. The blade rows are replaced by multi actuator-disks with different total-to-static characteristics. By added the correlation functions of inlet and outlet flow angles, we can compute the flow field by combining the Euler equations and the multi actuator-disks model. A two-stage low-speed compressor in NUAA has been investigated, and the predicted results indicates that the second stage comes out stall cell first, and the full developed stall cell rotates at about 40.4% rotor speed, which coincides with the experimental data.
To investigate the effect of high temperature steam ingestion on the aerodynamic stability of a multistage axial compressor, a two-stage low-speed axial compressor was studied, and full-annulus steady-state and unsteady-state numerical simulations were carried out. The effect of the high temperature steam mass fraction and the distribution of steam at the inlet boundary on the aerodynamic stability of a two-stage low-speed axial compressor was investigated. From the simulation results, we found that high temperature steam ingestion has an adverse effect on the low-speed axial compressor. The larger the steam mass fraction is, the greater the impact of the steam ingestion on the stability boundary and stall margin will be. When the steam mass fraction is equal to 0.35 and 0.7%, the stability margin decreases from 36.07 to 29.72% and 28.05%, respectively. The distribution of steam at the inlet boundary will change the performance and stability. When the steam ingestion range is less than 90°, the steam ingestion area increases and the stability margin will decrease gradually. After 90°, the stability margin is almost unchanged. The difference between the calculated and experimental values of the stability margin reduction caused by steam ingestion is 0.87%. In addition, with the ingestion of high temperature steam, the blockage in the corresponding passages is intensified and the loss is increased, which leads to the occurrence of the stall in advance. It is evident that steam ingestion has a significant impact on compressor stability, ensuring that the steam mass fraction and steam ingestion range are close to the actual value.
To investigate the effect of twin swirl and bulk swirl on the performance and stability of a transonic axial compressor, a blade swirl generator was designed and simulated with a transonic single rotor using steady and unsteady numerical calculation methods. The bulk swirl intensity was adjusted by replacing the blades with different camber angles. The twin swirl intensity was decreased by reducing the blade number. The counter-rotating bulk swirl generated a significant drop in both the efficiency and stall margin, and resulted in an increase in the choked mass flow, and total pressure ratio. The co-rotating bulk swirl generated a decrease in the mass flow, total pressure ratio and stable operating range. The counter-rotating bulk swirl resulted in suction surface boundary layer separation beyond 50% of the span-wise height as well as more serious tip leakage blockage. The twin swirl resulted in a decrease in the total pressure ratio, maximum efficiency and stable operating range. The steady and unsteady numerical calculation results were consistent, though some differences were observed in the values. For the steady calculation, the maximum efficiency and choked mass flow decreased by 0.88% and 1.74%, respectively, and the mass flow at the stable boundary increased by 3.92% as compared to the uniform inlet flow at twin swirl intensity of 24°. During the unsteady calculation, the mass flow exhibited an increase of only 2.2% at the stable boundary. Under twin swirl and co-rotating bulk swirl and uniform inlet flow, the leading edge spillage of the tip leakage flow resulted in compressor instability. The counter-rotating bulk swirl changed the mechanism of instability. The characterisation of the swirl distortion presented a difference between the steady and unsteady calculations near the stable boundary. The unsteady calculation exhibited a lower mass flow at the stable boundary point and a higher total pressure ratio.
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