A Tale of Magnets and Microphones: using a Magnetic Support and Balancing System (MSBS) for aeroacoustic wind tunnel testing

Abstract

In acoustic wind tunnel testing, strut noise can be a great nuisance if it dominates the sound field. A magnetic model support would be a solution to this problem, as it supersedes the need for mechanical struts. A magnetic support is however likely to interfere with the microphone signals in acoustic wind tunnel testing, if the microphones are not manufactured for use in magnetic fields. In order to determine the possibilities of using microphones in a wind tunnel with a Magnetic Suspension and Balance System (MSBS), tests were made in the Basic Aerodynamic Research Tunnel at Tohoku University in Sendai, Japan. Both, tests with a static cylinder and with a levitating model were made. Microphone signals were recorded alongside Hall probe signals in order to find the influence of the magnetic environment on the pressure fluctuation signals. Several distinct frequencies were identified at which an influence of the environment was detected.