Numerical analysis of time dependent external disturbances on separated axisymmetric nozzle flow

In overexpanded rocket nozzle flow at low altitudes, the sensitivity of the shock structure, that develops inside the expansion part of the nozzle, causes severe problems in modern nozzle design. This shock structure is highly unstable, so that small fluctuations in the flow field can lead to heavy asymmetric loads on the nozzle. The movement of the shock structure is analyzed numerically by imposing a periodically fluctuating pressure to an external boundary face. The effects on the sideloads are estimated by an unsteady axisymmetric analysis. The unsteady analysis shows, for the investigated frequency range, how the fluctuation propagates, the shock movement develops and sideloads are generated.