S弯收扩喷管流动特性数值研究

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.