Using CAE to Resolve Resonance in a Supply Fan Assembly of a Packaged Rooftop Unit

摘要

While studying field feedback reports, an HVAC engineer observed excessive vibration on a particular centrifugal supply fan assembly. The engineer studied this assembly and used a vibration analyzer to determine there may be a resonance (as even a dynamically balanced wheel was excessively vibrating at only certain RPMs that matched with the operating RPMs in the field reports). Using Finite Element Analysis, the engineer conducted a modal vibration analysis on this assembly to see if the assembly's natural frequencies fall within the operating range of this fan. After the natural frequencies (and their corresponding mode shapes) were identified from the modal analysis, a harmonic response analysis was conducted. A harmonic response analysis quantifies the vibration based on a sinusoidally varying load (which in this case is a defined unbalanced mass on the fan). CAE is the preferred method to start a redesign process as it is cheaper and faster to try different solutions. Once a new design did well in simulation, the engineer spent the resources manufacturing the design and validating the simulation physically for added confidence in the results. Leveraging CAE assisted in boosting the engineering quality of the centrifugal fan system and consequently the overall HVAC unit.