This paper describes a study of strategies used to limit the flow generated noise encountered in the outlet diffusers of high velocity heating, ventilation and air conditioning (HVAC) duct systems. A circular jet of air was expanded using a 7° conical diffuser with a variety of outlet configurations and pipe lengths. Sound pressures were recorded for a jet diameter of 50 mm and a jet velocity of 15–60 ms−1 using a dual room reverberation suite. The design of the diffuser outlet was found to have a pronounced effect on the noise spectrum radiating from the duct outlet. The length and shape of the outlet duct downstream from the diffuser directly affect the noise radiating from it. Results are presented for a variety of outlet pipe lengths and geometric configurations. A numerical simulation of airflow through the conical diffuser was also completed using a large eddy simulation (LES) turbulence model for a range of jet velocities. An acoustic post processor was then used to predict the corresponding far-field sound pressure and sound power levels.

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