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.
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.
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.