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针对一动叶采用缩放式叶型设计、以无导叶对转涡轮为应用背景的涡轮级,通过数值模拟进行研究发现,在设计换算转速下,该涡轮级效率特性呈现“双峰值”的特点.随着落压比增大,首先动叶进气攻角由负变为零,效率升高并达到极大值;其后,动叶流道内形成正激波,其自身产生波阻并在吸力面引起边界层分离,效率下降;随后,该激波向下游移至叶片尾缘,尾迹损失明显增加,加上波阻、边界层分离的综合作用,效率达到极小值;然后,该激波演变为尾缘斜激波,自身波阻减小,而且它在吸力面引起的边界层分离消失,流道内总体损失下降,效率又会上升并在设计点附近达到极大值;其后,该激波波前马赫数不断增大,波阻损失随之增加,同时尾迹损失也持续增加,效率又会下降.结果显示,高负荷跨音工况下激波与边界层干扰引起的边界层分离损失以及动叶高出口马赫数时尾缘区域的损失(包括波阻损失和尾迹损失)占总体损失的至少1/2以上,在设计优化过程中应重点关注与之相关的动叶吸力面扩张段和叶片尾缘区域.

Numerical simulations were implemented to study the efficiency characteristics of a turbine stage.The stage is intended for the use of the vaneless counter-rotating turbine and its rotor is designed with the convergent-divergent cascade passage.It was found the variation of the stage efficiency shows a "dual-peak" feature under the design corrected rotational speed.As the total pressure ratio increases,at first,the incident angle of the rotor goes from negative to zero,which results in an improvement of the efficiency to the first peak; after that,a normal shock wave forms in the rotor passage,which not only arouses loss itself but also gives rise to the boundary layer separation on the suction side,so the efficiency begins to decrease; as the shock wave moves downstream and reaches the trailing edge of the rotor,the wake loss is significantly improved and the efficiency achieves a minimum by the combined effects of the shock wave,wake and flow separation; then,the loss of the shock wave is reduced and the flow separation on the suction side disappears as the normal shock wave turns oblique,by the effects of which,the efficiency goes up again until the design point of the turbine at which a second peak of the efficiency is obtained; further,the loss of the shock wave rises due to the increase of the Mach number in front of the shock wave,and with the additional effect of the increasing wake loss,the efficiency goes down once more.The results show that the loss of the flow separation induced by the interaction between the shock wave and boundary layer,and that of the wake and shock wave in the case of high exit Mach number of the rotor account for more than one half of the total loss for highly loaded conditions; the associated regions including the divergent section of the rotor suction and the trailing edge of the rotor should arouse enough attention in the design of the turbine stage.