Surge model influence on surge wave propagation in serpentine inlet

The overpressure predictions associated with engine surge are essential when defining the peak loads in intake structure design. The present computational study investigates the phenomenon of engine surge to foresee the maximum pressure loads on an S-shaped engine intake. Four distinct surge models were evaluated, focusing on the effects of rise time, fall time, and maximum overpressure ratio (OPR) on the resulting pressure loads and flow field characteristics. The surge propagates upstream as a pressure wave from the aerodynamic interference plane, interacts with the separation region, and carries the distortion ahead. A sharp rise in the pressure within 2.5 ms creates pressure loads nearly 26% higher than the maximum OPR. Rapid pressure increases create strong shocks resembling shock waves, while gradual increases in pressure do not induce strong shocks but create a vast spillage area ahead of the duct. The high-pressure gradient created by the surge may accelerate the flow to supersonic speeds in certain regions. Post-surge, significant changes in flow structure are observed, including the formation of high vorticity zones near the intake lip and complex flow distortions throughout the duct. This study offers insights into the critical parameters affecting surge behavior, providing a basis for determining design limits and improving the robustness of intake systems subjected to extreme operating conditions.