Designing Automotive Rear Air Handling System for Low Flow Induced Noise using Broadband Noise Source and Ffowcs-Williams & Hawkings Models

To increase the comfort level of a vehicle cabin, vehicles today are equipped with rear cooling unit in addition to the primary heating ventilation and air conditioning (HVAC) system that supplies conditioned air into the cabin through the instrument panel (IP) duct and console or foot duct. Ducting for the rear unit is generally provided through C or D pillar and the roof of the vehicle. Owing to packaging and styling constraints, flow induced noise in roof duct has become a key parameter in design and development of the rear cooling unit.

This paper, broadly discusses:

• Two Broadband Noise Source (BNS) Models namely (i) Proudman’s model for quadrupole source and (ii) Curle’s boundary layer model for dipole source and
• Ffowcs-Williams & Hawkings (FW-H) model for noise level information at receiver location.

BNS model available in commercial Computational Fluid Dynamics (CFD) code Fluent^™ has been used as a design tool for identifying the critical zones of high noise level for further redesigning of the ducts for acceptable noise level. The performance of the complete rear air handling system (AHS) at cabin level along with the noise level at different receiver locations is then predicted by using FW-H model.

The comparative study of CFD analysis and real time experimental results confirm that rear AHS can be designed for low noise level using CFD approach with BNS model as a design tool and performance can be checked by FW-H model at receiver location, thereby reducing system development cost and time drastically.