Approximate modeling and optimization design of serpentine nozzle structural displacement based on multi-physics coupling

Low-observable serpentine nozzles are essential for the exhaust systems of new-generation stealth aircraft. Considering the complex spatial constraints and compact layout of serpentine nozzles, dual-stream serpentine nozzles with varying geometric characteristics were designed. The influence of three key geometric parameters, namely the nozzle exit aspect ratio (W_e/H_e), length-to-diameter ratio (L/D_in), and obscuration ratio (△Y), and their interactions with the structural deformation of the serpentine nozzle were investigated based on a sequentially coupled two-way Fluid-Structure Interaction (FSI) algorithm. Response surface models for structural deformation were established using the Box-Behnken Design (BBD) experimental design method and Response Surface Methodology (RSM), and the sensitivity of key geometric parameters to the deformation of critical nozzle locations was analyzed. The results indicate that each geometric parameter has varying degrees of influence on the deformation of different nozzle sections, and the coupling effects between parameters are significant. W_e/H_e primarily affects the deformation of the top exit wall, △Y mainly influences the deformation of the bottom exit wall and the downstream wall of the first bend, while L/D_in has a certain degree of influence on the deformation of all sections. With the objective of minimizing structural deformation while maintaining good aerodynamic performance, the serpentine nozzle was optimized using RSM, resulting in a 56.9% reduction in the total structural deformation.