Infrasound emissions from high-speed facilities are degrading the vibro-acoustic environment in their neighborhood. There is increasing pressure from regulatory agencies to set limits on infrasound emissions from new, as well as existing facilities. The purpose of this paper is to review the infrasound problems in wind tunnels, hush houses and gas turbine test cells to identify the cause of the infrasound phenomenon and to define further research needed in this area. Most of the work reported is related to fixes in supersonic wind tunnels and hush houses in the form of vortex generators, Helmholtz resonators and other massive silencing devices. The hypothesis that this phenomenon based on 'Chernekov radiation' caused by the high temperature gradients in the high-speed flow region in the augmentor tube needs further investigation. There is some undocumented evidence to suggest that these low frequency emissions are associated with engine test cell geometry and flow. Systematic data on engine and test cell operating parameters are required from the engine operators to identify the cause of this phenomenon. The effect of facility geometry on this radiation can be examined by scale model studies.
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