Acoustic protection on payload fairings of expendable launch vehicles

Numerical and experimental investigations on the acoustic performances of membraned Helmholtz resonators embedded in a porous matrix

“…For f <f 0 and f >f 0 the imaginary part of the HR, Y , is much more important compared with both the real part and the imaginary part of the foam material (see Fig.7 (b) and (d)). Equations (10) and (11) thus show that in this case, (…”

“…This inequality still holds for intermediary surface ratio r and X|Z M s | 2 /(1 − r)>>|X| 2 /r. In this case, equations (10) and (11) show that Re(Z PUC s )→X/r and Im(Z PUC s )→0: the surface impedance of the resonant PUC is controlled by the resonator. At the HR resonance frequency of both configurations, Fig.7 (b, d) show that the real part of the total surface impedance Re(Z PUC s ) decreases to reach the one of the HR and the imaginary part Im(Z PUC s ) increases to cross the zero axis.…”

“…A large amount of research is related to the wide use of HRs in a variety of technical applications in different fields of industry [7][8][9][10]. For aerospace application, a system used to protect the payloads against noise emission of expandable launch vehicles was proposed by [11]. It is based on the integration of tuned acoustic absorbers (HR with its neck integrated inside the cavity) in foamed plastic mats.…”

Experiment-simulation Study on Noise Reduction of Cylinder Shell with Horn Helmholtz Resonator

“…Liu Haitao et al [8] corrected the acoustic length of the air in the conical neck and obtained a modified onedimensional model of the conical neck HR's transmission loss. Borchers et al [9] designed a noise reduction device with a wide-band noise absorption performance, and the resonance frequency calculation formulas of the curved neck HR using a one-dimensional lumped parameter model are given. However, the design of the resonator is a difficult work for the reason that the modified parameters need to be obtained by experimental methods.…”

Broadband low-frequency sound transmission loss improvement of double walls with Helmholtz resonators

“…For example, Helmholtz resonators were also successfully applied to reduce the sound pressure level inside the payload fairing of launch vehicles. The broadband noise reduction was achieved using a horn-like neck shape of the resonator to cause high absorption at low frequencies, while at higher frequencies the absorption was generated by porous materials surrounding the resonators [10]. This 45 approach differs mainly in two aspects from the double wall with integrated Helmholtz resonators studied here: First, the Helmholtz resonators in the payload faring are designed to achieve high absorption in order to dampen the sound pressure levels occurring inside the comparatively small volume inside the fairing.…”