Abstract: In order to ameliorate the side load problem of the large area ratio overexpansion nozzle and improve the overall performance of the rocket engine nozzle， a technique scheme of morphing nozzle was proposed to reduce the side loads. Taking the expansion section of VOLVO-S1 nozzle wall as the basic research model， the cross-section of the nozzle wall in the X-axis direction was changed from circular to elliptical by applying a pair of symmetrical forces in the Y-axis direction. The area ratio of the nozzle and the flow path characteristics were changed so that the goal of reducing the side loads can be achieved. By using the numerical method for solving the Reynolds averaged N-S equation， the corresponding changes in the flow field of the morphing nozzle were carried out. The results show that after exerting a certain size force， the nozzle outlet area is reduced by 0.98%， the peak of side loads of morphing nozzle in the Y direction can be reduced to 60% of the original with a small thrust loss， at the same time， the side loads in the Z direction can be nearly made down to half of the original nozzle. Additionally， the transformation from freedom shock separation to restricted shock separation occurs at nozzle pressure ratio being 15.2～15.3 in the morphing nozzle， which is delayed compared to the shock mode transition of the VOLVO-S1 nozzle. Finally， the reason why the side loads are reduced in the morphing nozzle is analyzed.

Key words: Overexpansion；Side loads；Morphing nozzle；Area ratio；Shock separation

摘要： 为了改善大面积比过膨胀喷管的侧向力问题，提高火箭发动机喷管的整体性能，提出一种变形喷管抑制侧向力的技术方案。以VOLVO-S1喷管扩张段壁面为基本研究模型，通过在Y轴方向施加一对对称作动力后，使得喷管扩张段壁面沿X轴方向的各截面由圆形变为椭圆形，以此来改变喷管的面积比和流道特性，从而实现减小侧向力的目标。运用求解雷诺平均N-S方程的数值方法，对上述变形喷管的流场变化开展了相应研究，结果表明:在施加一定大小作动力后，喷管出口面积减小约0.98％，变形后的喷管相比于原喷管在推力损失较小的情况下可以将Y方向侧向力的峰值降为原来的60%，同时可以使得Z方向的侧向力峰值降为原来的一半。此外，变形喷管在落压比为15.2～15.3期间发生自由激波分离向受限激波分离的转换，相比于VOLVO-S1喷管的激波模式转换会有所延迟。最后分析了变形喷管的方案导致侧向力降低的原因。

关键词: 过膨胀；侧向力；变形喷管；面积比；激波分离