PO 107‐5 Preliminary Results from Tests on Two Tracer Gas Protocols Developed to Determine Ventilation Flow Rates and Patterns in Naturally Ventilated Munitions Storage Bunkers

PO 107‐1 Design, Development and Evaluation of a Noise Control Enclosure for a Model Jet Engine J. Black, J. Rinker, R. Yon, C. Holder, U.S. Air Force, Wright‐Patterson AFB, OH; J. Slagley, School of Aerospace Medicine, Wright‐ Patterson AFB, OH. Situation/problem: A cart‐mounted model jet engine used for educational demonstrations produced a sound pressure level (SPL) of 89.1 dB at a distance of 25’, the minimum safety distance determined for operating the jet engine at full power. Design, development and evaluation of an engineering noise control to lower the SPL attributable the jet engine to less than 80.0 dB at a distance of 25’ was requested by the jet engine’s owner. Resolution: A noise control enclosure (NCE) that would reduce the SPL of the jet engine to less than 80.0 dB at a distance of 25’ was designed, built and tested. The NCE is a wood frame rectangular box 27” x 48” x 24 1/8”, with 3/8” thick Plexiglas sides, special intake and ducted exhaust ports, a hinged side access window, and is directly attached to the existing jet engine cart with minimal modifications. The NCE’s predicted SPL reduction was based upon actual SPL frequency measurements, a blade pass frequency (BPF) analysis, and published transmission loss factors for the materials used to build to the NCE. Results: The NCE reduced the SPL attributable to the jet engine when operating at full power to 76.4 dB at a distance of 25’ and met all other owner desired use characteristics, such as ease of portability and not inhibiting viewing the jet engine. Lessons learned: NCEs are effective in reducing the SPL for hazardous noise sources and can be readily designed using basic noise control principals and published transmission loss factors. BPF analysis is of modest utility for predicting the dominant sound generating frequencies of devices that are not simple, rotating fans, and should be best regarded as a technical tool of interest for such cases. Actual SPL frequency data should be used to best design frequency‐dependent NCEs