This paper was produced for the 2019 NAFEMS World Congress in Quebec Canada
The complexity of the engineering and design of road vehicles is radically increasing. This is in part because vehicles are no longer perceived just as modes of transportation. They represent, in the eyes of the consumer, a personal space where unprecedented levels of comfort and technological refinement should be met. Acoustics play a large role in the comfort of a vehicle cabin, and over the last few years, the simulation and testing of external aero-acoustics and NVH of vehicles has driven constant improvements in cabin acoustics. Aero-acoustic simulations have up until recently mostly focused on exterior wind noise, accounting at high speed for a large part of the interior cabin noise at higher frequencies. Improvements in electric technologies have led to the commercialization of fully electric vehicles. The issues with windnoise at high speed in these vehicles are even more noticeable, as all noises from the internal combustion engine and exhaust are absent. Furthermore, at idling and low speeds, previously overlooked sound sources caused by cabin amenities are becoming predominant. Fans and blowers used to improve the thermal comfort of the passenger are now polluting an otherwise near silent cabin. Consumers have identified the Heating, Ventilation and Air Conditioning unit (HVAC) noise to be one of the main culprits. The problem is preponderant in electric vehicles, but also a cause for concern for ordinary ICE vehicles as significant progress is made to reduce other noises. The HVAC unit is responsible for the heating, cooling and defrosting of the cabin, and its design space is often constrained heavily by other essential components of the vehicle. Although rapid prototyping of parts for an HVAC, and therefore testing, can be applied in fairly early stages of development, it is challenging to understand the noise generation mechanisms for this complex internal flow device solely through time consuming testing. Simulation of HVAC units has been similarly demanding to implement, as these HVAC devices operate at very low flow velocities, and the acoustics they generate are difficult to capture accurately. In this paper, we will present simulation results for an HVAC unit from a BMW series vehicle using SIMULIA PowerFLOW, a Lattice Boltzmann based solver. Lattice Boltzmann based methods present low amounts of numerical dissipation, can deal with complex geometries, and are therefore the most suitable for this acoustic problem. We will demonstrate which noise source generation mechanisms are dominant within the HVAC system using the proprietary FIND (Flow Induced Noise Detection) Contributions post-processing method, and will present results from design iterations tackling these noise sources. Once we have established how sensitive the noise sources are to individual design changes, a full aero-acoustic optimization will be conducted. An optimum will be deduced from a response surface analysis and compared back to the original baseline to assess the effectiveness of the optimization.
|Date||18th June 2019|