Airborne Noise Mitigation for Roof-Mounted Air-Conditioning Unit Using Simulation-Based Flow-Induced Noise Detection Approach

<div class="section abstract"><div class="htmlview paragraph">In the current world of automobiles, the air-conditioning system plays a crucial role in passenger comfort. Thermal comfort for the passengers, which was earlier a luxury, has now become a basic necessity. This thermal comfort, coupled with ventilation, brings along with it the symbiotic association of flow-induced noise. The subjective prominence of airborne noise from air-conditioning systems increases with higher refinement or masking of structure-borne noise and/or engine noise sources. These systems for commercial vehicles are higher in capacity, complex, and generally placed directly above the passenger seats. Flow-induced noise refinement for such systems is generally difficult and involves multiple physical trials.</div><div class="htmlview paragraph">In the current work presented for a commercial van, the airflow delivery of the air-conditioning system was in line with the requirement. The location of the system, however, resulted in higher noise levels at the passenger ear location. To address this issue, an analysis-based mitigation strategy was developed based on the ranking of noise sources identified along the flow path. In-cabin flow-induced noise was simulated through three-dimensional computational fluid dynamics by using a transient, compressible, explicit aero-acoustic lattice Boltzmann method-based solver. The process accurately captured the turbulent and convective flow mechanisms that result in acoustic noise propagation.</div><div class="htmlview paragraph">Noise mitigation was achieved by multiple design iterations to balance the acoustics and air-handling parameters. The final optimized design was physically tested, and the improvements observed were in line with the simulation trends. The airflow path, blower housing, and return air grill were the major areas of improvement to reduce airborne noise inside the vehicle cabin. The optimized design was able to reduce the noise levels by 7.5 dBA while increasing the airflow delivery of the system. By minimizing flow-induced noise discomfort, the approach has enhanced the customer thermal comfort by improving the system efficacy.</div></div>