The effect of the acoustoelastic interaction in forming the acoustic loads under the fairing of the rocket head

The paper deals with the theoretical study of the sound field forming in the under-fairing space of the rocket head. The nature and properties of the sources of external acoustic loads on the rocket body are analyzed at different stages of the flight. At its beginning, the influence of the gas-dynamic sound sources located in the rocket jet prevails. In the transonic interval of atmospheric flight, turbulent wall pressure fluctuations in the surrounding flow play the main role in the acoustic loads on the surface of the rocket body. Computations show that the jet noise has higher levels, and therefore, the starting interval is the most unfavorable from an acoustic point of view. To assess the efficiency of sound transmission from the outer surface of the rocket body to the under-fairing space, a simplified two-dimensional acousto-elastic model is proposed. Within its framework, the main part was modeled by a thin-walled elastic infinite cylindrical shell surrounded on both sides by an acoustic medium. The presence of the payload was simulated by an acoustically rigid insert inside the shell. The corresponding coupled boundary value problem was formulated and analytically solved to obtain expressions for shell deformations and acoustic potentials in the form of convergent series. This allowed us to investigate the behavior of the sound field under the fairing in a wide frequency range. It was noted that the frequency dependence of the maximum sound level on the surface of the insert contains numerous high-Q peaks. They correspond to the resonances of the system formed due to the acousto-elastic interaction occurring at longitudinal-flexural vibrations of the air-filled shell. The efficient excitation of the circumferential eigen modes of the shell vibrations plays a key role in the formation of dangerous acoustic loads. This conclusion is confirmed by the obtained spatial distributions of the sound field at the corresponding frequencies.