Wind tunnel study on vortex-induced Helmholtz resonance excited by oblique flow

A wind tunnel study examining the vortex-induced internal pressure dynamics of a rigid structure with a single dominant opening in laminar flow is presented. The internal pressures in a rigid structure configured with three different openings and two different internal volumes were measured under four different incoming wind velocities and different wind angles from 0° to 90°. The mechanism of vortex-induced internal pressure dynamics under oblique wind was explored, and the effect of Strouhal number on the vortex-induced internal pressure dynamics was investigated. It was found that vortex shedding is produced across the orifice under grazing flow, and a significant double resonance phenomenon may appear in the internal pressure spectra. Vortex-induced internal pressure resonance may occur in some cases, which leads to a significant increase in internal pressure pulsation. Wind velocity, wind angle, Helmholtz frequency, and the opening width exert a significant influence on the frequency and amplitude of the internal pressure resonance characteristic. Theoretical estimation about Helmholtz frequency and vortex shedding frequency is of good reliability but it is not suitable if the interaction of vortex shedding and Helmholtz resonance is significant enough. The Strouhal number is an important parameter in the evaluation of vortex-induced internal pressure resonance, and the vortex-induced internal pressure resonance is more likely to occur when the Strouhal number, expressed as fHw0/U0 (U0 can be estimated as U sin θ or measured by a cobra probe), lies within the range of 0.2-0.7. The Strouhal number, expressed as fHw0/U, can be used to access the internal pressure resonance characteristic at different wind angles.