Numerical Investigation Of Bowed And Swept Rotor In A Transonic Axial Compressor

As one of the essential components of an aero-turbine engine, the compressor is developed reaching higher pressure ratio with less stages, larger mass flow at unit up-wind area, higher efficiency, larger stall margin and less weight and component amount to meet the demand of larger thrust-weight ratio of the engine. New technique problems appear continually in the compressor design process, thus the aerodynamic design of high-load compressor is always a challenge in the development of aeroengine.On the base of 3-D analysis, blade bowing and sweeping technique is to design blade considering the combined effects of bowing, sweeping and twisting. The sweeping technique, especially forward sweeping one has been employed to weaken tip shock of rotor. And the bowing technique has been applied to improve endwall flow condition, reduce endwall flow loss, and make the blade geometry more adaptive to the flow, consequently to increase work ability and performance of the blade. As important means to control endwall secondary flow and shock wave, blade bowing and sweeping technology have been widely applied in compressors and fans to achieve higher efficiency and larger stall margin. However due to the deficiency of experiment, the knowledge of acting mechanism of bowed and swept rotor is still limited. Thus detailed parametric researches on such mechanism of bowed and swept rotor in a transonic compressor are carried out, and the effects of rotor bowing and sweeping on the wake transportation, the pressure fluctuation at downstream stator surface, the interaction of rotor and stator, and stage performance are detailedly analysed.Since studies have shown that forward sweep and positively bow are able to increase stall margin and improve endwall flow of compressor, parametric researches on forward sweep and positively bow applied in a transonic rotor are done, and the effects of two parameters, bow/sweep height and bow/sweep angle, on the performance are detailedly analyzed. Results show that the efficiency is improved with both design techniques. It's also shown that larger bow/sweep height or bow/sweep angle, which is profitable to tip flow condition, is harmful to mid performance, and such adverse effect is more evident when increasing bow/sweep angle. Hence a large bow/sweep height and a moderate bow/sweep angle are adopted in the final rotor modification.Based on the achievement of parametric researches, a principle for rotor modification is obtained. The principle includes large bow/sweep height, moderate bow/sweep angle, and redesigning three sections at rotor central part by reducing chord length and increasing turning angle to weaken shock intensity and decrease separation loss there. The modified rotor with such principle is with increased efficiency by 3%, improved stall margin form 18% to 26%, and higher pressure ratio at small mass flow condition. Therefore, an obvious compressor compressor performance is obtained. The successful modification also proves the essential role of mid sections optimum design on applying bow/sweep technique in rotor design to improve compressor performance.The development of nowadays turbomachine put forward increasing requirement of high aerodynamic performance and reliability, which challenges the traditional design and research technique on the basis of simplified steady flow assumption, thus advanced technique is in developing. The advanced technique, otherwise, relates to detailed research and deep understanding of unsteady effect. In the present paper, numerical simulations on the effects of the bowed and swept rotor on the unsteady flow field in a single stage axial compressor are carried out. Compared to the baseline, the phases of the time-dependent stage efficiency and total pressure ratio fluctuation wave are shifted as a result of the phase shift of the rotor wake and the potential flow in the compressor with bowed or swept rotors. The stage efficiency is remarkably increased and the fluctuation amplitude is evidently reduced because the curved rotor lowers the endwall loss and increases the radial uniformity of the inlet boundary condition of the downstream stator.In comparison with the baseline, in the curved rotor stage, the amplitude of the static pressure fluctuation decreases at the two endwalls, but increases at mid-span near the leading edge of the stator. The radial distribution of the unsteady blade loading is more uniform, which is beneficial for guaranteeing the intensity of the blade leading edge. Downstream the curved rotor, except for the stator leading edge area, the amplitude of the static pressure fluctuation decreases in the tip region of stator surface, but undergoes no obvious changes in the middle and at the hub. This is ascribed to that, in the curved rotor stage, the dissipation of the rotor wake at mid-span is slower than that at the two endwalls, and the rotor wake moves towards the hub under the influence of radial pressure gradient during the downstream migration.Bowed and swept rotors reduce the unsteady disturbance on the aerodynamic loads of downstream stator, so as to decrease the fluctuation amplitude of aerodynamic loads parameters, especially that of aerodynamic moments. And the amplitude of 1.BPF falls obviously in the frequency spectrum of aerodynamic loads of rotor and stator, due to lightened unsteady rotor/stator interaction.