Bus Cabin Noise Prediction of Large HVAC System Using Total Noise Method

HVAC system design has an accountability towards acoustic comfort of passengers of a vehicle. Owing to larger cabin volume of a bus, multiple air blowers have to be installed to ensure comfort of passengers. Such multiple blowers produce significant flow induced noise inside the cabin. For commercial success, it becomes essential to predict intensity of such a flow induced noise at very early stages in product development. Conventionally sliding mesh based CFD approach is deployed to predict flow and turbulence noise around each blower. However due to complexity, this method becomes computationally intensive resulting in cost and time inefficiency. Hence it is desirable to innovate around an alternative rapid, reliable prediction method, which ensures quick turnaround of prediction. This paper describes a unique innovative approach developed around a multiscale method where flow induced noise generated by a single blower in motion is predicted using commercial Lattice Boltzmann CFD software with a digitally scaled down HVAC system in an anechoic digital wind tunnel. These CFD predictions are used to replace all blowers with virtual stationary speakers inside digital cabin to emulate noise emanated by a large HVAC unit. Authors named this method as total Noise Multiscale Approach, in the paper. With the total multiscale approach, overall sound pressure level predicted inside the bus cabin at rear passenger ear levels are comparable with the physical test measurements and has shown fair correlation. Using this multiscale total noise method, computational cost and turnaround time has significantly reduced compared to the flow conventional resolving approach for cabin with all the blowers. This predictive total noise method found useful in designing and planning countermeasures during product development.