Abstract: In order to investigate the flow mechanism of serpentine convergent-divergent nozzle， the numerical simulation on the flow characteristics of serpentine convergent-divergent nozzle with different nozzle pressure ratio （NPR） and exit area ratio of serpentine convergent duct （A₇₂/A₈） had been performed. The results show that with the increase of NPR in the highly over-expanded conditions of serpentine convergent-divergent nozzle， the unsymmetrical flow separation turned into symmetrical flow separation and the λ shock turned into Mach disk， which bringed about the decrease of aerodynamic performance and vector angle. As NPR continued to rise， shock waves moved toward the nozzle outlet， and gradually transformed into an expansion wave. As a result， the aerodynamic performance increased， and the vector angle remained unchanged after decreasing to 0°. Under the low observable qualifications of totally shielding the high-temperature components， the change of A₇₂/A₈ notably impacted on the flow characteristic in the convergent duct， mainly reflecting in the local acceleration and secondary flow in the serpentine convergent duct. And the performance of the serpentine convergent-divergent nozzle increased with the increment of A₇₂/A₈. While A₇₂/A₈ increased to 1.8， the flow separation occurred on the upper wall of the first serpentine duct， inducing the notable decrease of aerodynamic performance.

Key words: Serpentine convergent-divergent nozzle;Flow characteristic;Aerodynamic performance;Nozzle pressure ratio;Exit area ratio

摘要： 为了研究S弯收扩喷管的流动机理，数值模拟了不同喷管落压比（NPR）和S形收敛管道出口面积比（A₇₂/A₈）对S弯收扩喷管内流动的影响。结果表明：当S弯收扩喷管处于高度过膨胀状态时，随着NPR升高，非对称分离逐渐转变为对称分离，λ型激波转变为马赫盘结构，气动性能下降，推力矢量角减小；随着NPR继续上升，激波从喷管内移动到喷管出口边缘，并逐渐转变为膨胀波，气动性能上升，推力矢量角减小至0°后保持不变。在完全遮挡高温部件的低可探测准则的约束下，出口面积比A₇₂/A₈的变化主要对S弯收扩喷管收敛段的流动特性产生显著影响，体现在S弯收扩喷管内的局部加速及二次流分布。S弯收扩喷管的气动性能随着A₇₂/A₈增大而提高，但当A₇₂/A₈增大至1.8时，第一弯管道出口上壁面发生流动分离，气动性能显著下降。

关键词: S弯收扩喷管;流动特性;气动性能;喷管落压比;出口面积比