Evaluation of the Aeroacoustic Sources of a Swirl Diffusor

The acoustic noise generated by air diffusers can have negative impacts on a productive working environment and thus is a considerable limiting factor in ventilation systems. A reliable prediction of sound sources and levels offers the potential to minimise noise emissions in the early design process of air diffusers. In this work, we investigate a commercially available swirl diffuser. For a complete coverage of all flow and acoustic phenomena, the swirl diffuser is only slightly modified and modelled with transient flow simulations. We use large-eddy simulations coupled with the perturbed convective wave equation to model the flow and the aeroacoustic behaviour. The diffuser can be operated over a wide range of volume flows. To limit the computational cost, we investigate the diffuser at three operating points (278, 414 and 549 m3/h). To validate the computed aeroacoustic behaviour we use acoustic measurements. Laser-Doppler-Anemometry measurements are carried out to validate the flow simulation. The transient model is able to predict a sound spectrum and attribute certain features of the spectrum to geometric features of the air diffuser. Furthermore, the flow structures responsible for the sound are determined. These insights can offer guidelines for future designs of comparable air diffusers.