Chamber Core Structures for Fairing Acoustic Mitigation

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information AFRL-VS-PS-JA-2007-1013 SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)AFRL/VSSV SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release; distribution is unlimited. ‡ SUPPLEMENTARY NOTESPublished in the Journal of Spacecraft and Rockets, Vol. 44, No. 1, Jan -Feb 2007 ‡No public affairs clearance on file (DTIC Codes 1,20). ABSTRACTThe U.S. Air Force Research Laboratory is pursuing an innovative composite structure design called chamber core for constructing launch vehicle payload fairings. A composite chamber core fairing consists of many axial tubes sandwiched between face sheets, tubes that can be used as acoustic dampers to reduce low-frequency interior noise with virtually no added mass. This paper presents the results of experimental studies of noise transmission through a 1.51 m diameter x 1.42 m tall chamber core cylinder. It was tested in a semireverberant acoustics laboratory using band-limited random noise at sound pressure levels up to 110 dB. The bare cylinder provided approximately 12.7 dB of attenuation over the 0-500 Hz bandwidth and 15.3 dB over 0-2000 Hz. The noise reduction increased to over 18 dB for both bandwidths with the axial tubes acting as acoustic dampers. Narrowband reductions in excess of 15 dB were measured around specific acoustic resonances. This was accomplished with virtually no added mass to the composite cylinder. Results were compared with the performance provided by a 2.5 cm acoustic blanket treatment. The acoustic dampers were as effective as the acoustic blanket at low frequency, but not at higher frequencies. The acoustic dampers were better able to couple with and damp the low-frequency acoustic modes. Together, the acoustic blanket and dampers provided over 10 dB more noise reduction over the 2000 Hz bandwidth than the bare cylinder. The U.S. Air Force Research Laboratory is pursuing an innovative composite structure design called chamber core for constructing launch vehicle payload fairings. A composite chamber core fairing consists of many axial tubes sandwiched between face sheets, tubes that can be used as acoustic dampers to reduce low-frequency interior noise with virtually no added mass. This paper presents the results of experimental studies of noise transmission through a 1:51 m diameter 1:42 m tall chamber core cylinder. It was tested in a semireverberant acoustics laboratory using band-limited random noise at sound pressure levels up to 110 dB. The bare cylinder ...

Sound Transmission Loss Through a Corrugated-Core Sandwich Panel With Integrated Acoustic Resonators

“…imaginary part of the impedance) equals zero. Therefore the first resonance, or natural frequency, of the cavity can be written as: (6) For the second special case, it is assumed that the acoustic wavelength in the fluid is much longer than the dimensions of the resonator. In this case a lumped parameter model is appropriate.…”

“…This trend is predicted by both Eqs. (6) and (9) for quarter wavelength and Helmholtz resonators, respectively. Notice that while the peak response increases with frequency, this is due to the fact that the transmission loss of the bare panel increases with frequency.…”

“…To address this issue for launch vehicle applications, Lane et al [5,6] proposed using a double-wall fairing with long rectangular chambers sandwiched between 2 This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.…”

Simple Technique for Precise Measurement of Transmission Loss of Planar Sound Waves

“…S OUND transmission through a fuselage panel has been studied widely for aerospace applications [1][2][3][4][5][6]. For example, it is a critical issue to minimize the cabin noise when developing a new aircraft with a quiet and comfortable cabin.…”

“…Acoustic noise from the rocket engines is considered one of the severe problems in launching. A payload inside of a faring may be damaged by the strong vibration and the acoustic noise [5][6][7][8]. The acoustic noise has been reduced by the elaborate designs of the fuselage structure.…”