Investigation on the Vibration Response to High-Intensity Pressure Waves During a Solid Rocket Motor Operation

Launch vehicles experience peak vibro-acoustics stress during its captive firing or liftoff. The starting pressure rise transient in solid rocket motor chamber and subsequent flow of supersonic jet exhaust from the rocket nozzle generate high-intensity pressure waves. These pressure waves with different wavelengths are capable of exciting various structural elements of the launch vehicle. Especially the panel type of structural components located in very close vicinity to the supersonic jet and coming directly in the path of high-intensity pressure waves experience significant vibration. Hence, it is imperative to assess the vibration response of typical panel structures to high sound-level environment near the supersonic jet. Particularly, in the near field, these pressure waves behave in a nonlinear manner. Hence, developing a transfer function between vibrations to acoustics is essential for the proper design of structures for dynamic environment. In the present investigation, a typical panel structure instrumented with microphones and accelerometers are mounted near to a scaled down solid rocket motor supersonic jet exhaust. The plate is analyzed for its modes and frequency response function (FRF) by both experimental modal analysis (EMA) and finite element analysis (FEA). Also, the critical frequency of the plate is found out theoretically. The inclination of the plate with respect to the jet axis is varied for investigating the interaction of impinging and grazing waves. Further, the microphone and accelerometer measurements for different inclinations of the panel are analyzed by deriving power spectra and correlation functions. The ignition overpressure (IOP) wave interaction with the panel during the startup of the solid rocket motor is corroborated with the accelerometer response in the time domain. The high-intensity nonlinear Mach wave’s interaction with plate is analyzed from microphone and accelerometer time series data. The skewness of microphone and accelerometer data are compared. Finally, the frequency-dependent transfer function of vibration response to acoustic power input and vibrational efficiency factor is derived.