Mitigation of Community Noise from a Vacuum Excavator Using Simulations

Off-highway equipment operates in residential communities and must meet their radiated noise targets to be compliant with noise regulations and to be competitive in the marketplace. Traditional find and fix noise testing of late-stage prototype designs may cause launch delays, with intense time pressures that often result in missed opportunities to create excellent products with good value. Accurate simulation of noise from these machines allows noise targets to be assessed at each stage of product development, giving engineers time to develop low noise products without adding excessive manufacturing cost. Simulation of an early prototype of a new vacuum excavator showed excessive levels of radiated noise in two different frequency ranges. Further investigation of the simulation results of these two spectrum ranges indicated different noise mechanisms producing the excessive noise levels. An acoustic resonance was excited in the exhaust flow downstream of a silencer by highly vortical flow through a ninety-degree elbow. Broadband flow noise was also being generated downstream of this silencer, in a higher frequency range. Solutions to the two separate noise issues were developed by the design team using simulation. When the final design was manufactured and tested, the predicted noise reduction in the different spectrum bands was substantially achieved and overall noise reduction of 5-9 dB(A) was verified. Application of combined noise and flow simulation was found to enable on-time release for this new equipment, allowing better performance to be achieved without excessive cost.