Identifying and optimizing the aeroacoustic source regions of a slot air diffuser

Abstract

Although the primary goal of ventilation system is to maintain thermal comfort by providing conditioned fresh air to indoor environments, they also emit noise borne from the airflow itself. Air diffusers are the last component of a ventilation system and therefore their acoustic emissions can not be reduced easily by including silencers. Therefore, this paper presents a methodology to identify the aeroacoustic source regions. Using this methodology, targeted measures to reduce noise emission of a slot air diffuser are developed. A coupled aeroacoustic flow model for the investigated slot air diffuser is developed using the commercial software STAR-CCM+. Employing aerodynamic measurements, Laser-Doppler anemometry and acoustic measurements with a low-noise microphone the computed flow results are validated within a tolerance of up to

and

. The primary aeroacoustic source regions are identified and then localized by evaluating the sound pressure level at several receiver locations and on cut-sections of the diffuser. It is found that the flow regions inside the slots are primarily responsible for the acoustic emissions. A geometric modification is proposed that effectively prevents the development of a large-scale recirculating flow structure in the slots. The modification leads to a reduction of the overall sound pressure level by

. The modification is manufactured as a prototype which achieves a reduction of the measured sound pressure level by

. The achieved reduction of sound emissions enables an increase of the volume flow rates without violating regulatory limits on the perceived sound pressure level or an increased acoustic comfort at the same volume flow rate. This paper provides valuable insights into the optimization of slot air diffuser or similar devices during the early development stage. The presented results can serve as baseline for the development of more simple flow models to save on computational effort.