Aeroacoustics of tandem cylinders in crossflow - application to fan guard grills (vor Ort)
* Presenting author
Abstract:
Due to the progress on noise reduction of axial fan blades, the guard grill becomes a major noise source. It contains a number of narrow spaced rings designed to prevent persons from touching the rotating blades. Thus, these rings are placed in the turbulent wake of the fan blade and the major sound generation mechanism is cylinder vortex shedding. Previous publications on narrow spaced tandem cylinders show a strong dependency of the fluctuating forces on angle and distance. Microphone measurements for two cylinders in crossflow were conducted in an aeroacoustic wind tunnel. The results show dependencies of the noise emission on angle and distance in agreement with published literature. Inflow turbulence is found to affect not only broad band noise emission, but also level and frequency of the vortex shedding peaks. A splitting into two Strouhal peaks was found for many angles and distances, which has also been reported for force measurements. In order to be able to use the measured data for the derivation of a prediction model for guard grill noise, an interpolation method was used to approximate the measured spectra and to interpolate to the conditions found in the wake of the fan blade from CFD simulations.
