At liftoff, launch vehicles are subjected to a very severe overpressure and to an acoustic environment which can induce loads acting on payloads in the low-frequency domain (frequencies lower than 40 Hz). The overpressure starts at ignition of solid rocket motors. This overpressure phase is followed by the acoustic phase. The liftoff acoustic environment is generated by the rocket exhausts and by their impingement on the launch pad. For a numerical prediction of the acoustic environment, the European Aeronautic Defence and Space Company (EADS) has developed an inverse method via a tune domain boundary integral equations approach using an optimal control method, with direct and adjoint equations. The corresponding discrete schemes are highly accurate and unconditionally stable. As an industrial application, the identification of sources of overpressure is shown, which occurs at solid rocket motor ignition ARIANE 5. Having localized and characterized the sources from overpressure phase measurements in the time domain, the complete pressure environment is recovered. By integrating the resulting pressures over all surfaces of the launchers, the loads created by the liftoff overpressure field can be estimated. To achieve this identification, the 511 ARIANE 5 flight, which was instrumented, has been chosen. After identification of the overpressure sources, the pressures restored by direct calculation are compared with measurements. Last, an analysis of the robustness of the approach is presented.
展开▼
