Abstract: Hammershock loading is caused by engine surge, and is the maximum loading in the inlet structure design. To understand the dynamic characteristics of the hammershock, unsteady numerical investigations on the flow inside the M2129 S-shaped inlet are conducted. An unsteady back pressure boundary condition at the exit of the inlet is used to simulate the overpressure during engine surge. The detailed time history of the pressure and flow field inside the duct during the hammershcok are presented at the condition that the free-stream Mach number is 0.65 and the initial corrected mass flow is 60 kg/s (the Mach number at the exit of inlet is 0.44). It is found that the peak pressure inside the inlet duct can be at least 2.3 times of the free-stream static pressure. The backwards flow and the three-dimensional flow structure can be found at the downstream of the hammershock. After the engine surge occurred, it takes about 0.185 s for the flow inside the inlet to return to the steady state. This work also discusses the effects of the corrected mass flow, hammershock over pressure ratio and the S-duct's centerline. It is found that the peak pressure on the duct is higher and the hammershock spreads faster at a lower corrected mass flow condition or a higher over pressure ratio. The centerline curvature distributions can affect peak pressure distribution. A higher peak pressure appears at the sections of larger curvature.

Key words: hammershock, S-shaped inlet, dynamic characteristics, surge, numerical simulation