Wind tunnel resonances and Helmholtz resonators
Keywords:Computer simulation, Helmholtz equation, Natural frequencies, Pressure effects, Resonators, Vortex flow, Helmholtz resonators, Jet wind tunnels, Pressure fluctuations, Wind speed
AbstractOpen jet wind tunnels can be impacted by low-frequency pressure fluctuations due to different feedback mechanisms coupling with vortices shed from the nozzle exit. These fluctuations can reduce the simulation quality of the wind tunnel and/or reduce the effective wind speed range of the facility. Considerable research has been conducted to understand the on-set of these strong pressure fluctuations and different mitigation methods have been attempted to reduce these fluctuations. The idea of using Helmholtz resonators to provide strong absorption in the low frequency regime has been around for a long time in different acoustical applications. It has been applied in aero-acoustic fields also to control cavity resonances. A parametric study of applying Helmholtz resonators to control the pressure fluctuations in open-jet wind tunnels was undertaken. An existing open-jet tunnel was modified to produce strong low-frequency pressure fluctuations. A control volume to represent a Helmholtz resonator was attached to the wind tunnel. The control volume was made adjustable to produce different tuning frequencies to control fluctuations at different wind speeds. The results of the study are presented in this paper.
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