Aeroacoustic Optimization of a Metacage to Block the Noise Emitted by an Exhaust Fan
AbstractIn buildings, HVAC systems are taking care of air quality by exchanging polluted air for fresher one. However, they generate noise pollution disturbing the occupants. The challenge of allowing air to flow freely into the system while preventing noise from exiting is quite significant. Here is presented a solution by using an acoustic cage made of metamaterial, known as a metacage. It is constructed of sonic crystals arranged in a certain pattern which follows Bragg's law to a first approximation. Then, the shape and arrangement of the metacage and its crystals is obtained by computational experiments using Latin Hypercube Sampling (LHS). This makes it possible to create a metamodel with few experiments and find an optimal concept for the case studied, using only Open-Source software. A prototype was manufactured and tested, with and without airflow, on a bathroom fan according to different measurement standards. Comparisons with predictions are good, resulting a noise reduction of 2.3 to 1 sone, which represents 5.5 dB in terms of sound power.
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