Flow induced noise of resonators on the charged air side – arguing from theory, test stand measurements and simulations to solutions

Downsized combustion engines often need resonators subsequent to the compression of the incoming air to reduce the noise caused by the compressing process or by the huge amount of air flow. A well-tuned resonator attenuates the noise in a broad frequency range and therefore prevents noise radiation into the engine compartment and finally into the cabin. Typically, these resonators utilize the Helmholtz principle which is leading to a minor pressure drop and almost unaffected air flow. Current resonators have two to six chambers, which allow huge attenuation in a broad frequency range; e.g. common values are frequency ranges from 1000 to 4000 Hz with a transmission loss of 25dB. However, resonators on the charged air side cannot only reduce the propagating noise in ducts, they can also produce unwanted tonal noise which can be recognized in the cabin. This noise is flow induced and arises at the slots or holes of the resonator. As producer and market leader for resonators on the charged air side the company Umfotec uses a more pragmatic approach to understand the reasons for such unwanted flow induced noise especially in the context of resonators. It can be shown that different mechanisms are the root causes of flow induced noise and they require individual solutions for each root cause without influencing the desired transmission loss effect. Based on three different theories to describe the creation of flow induced noise by resonators in combination with test stand result this flow induced noise can be reproduced and evaluated. These test stand results with simple resonator designs are also simulated via CAE methods. Based on the verified and validated simulation model it becomes possible to work out solutions also applicable to series production. One of those solutions will be presented. This solution is also proved with a current serial resonator which had tendencies to flow induced noise. It can be shown that the flow induced noise is fully prevented while the transmission loss is even improved.