Simulating HVAC Noise in Vehicle Cabin with Material Absorption Modelling

Design of HVAC system plays an important role in acoustic comfort for passengers. With automotive world moving towards electrical vehicles where powertrain noise is low, designing low noise HVAC system is becoming more important. For an automobile manufacturer, ability to predict the production vehicle cabin noise at the early design stage is important as it allows more freedom for design changes, which can be incorporated in the vehicle at lower cost. Although HVAC prototype and system level testing at early design stage is possible for noise estimation but flow field is not visible in test that makes difficult to improve design. CFD simulation can provide detailed information on flow field, noise source strength and location. But in such a simulation, accurate prediction has been a challenge due to the inability of CFD tools to model acoustic absorptive characteristics of interior walls of cabin. This paper focusses on prediction of air borne noise of HVAC system inside a vehicle cabin using a commercial Lattice-Boltzmann computational fluid dynamics software. This paper explains vehicle cabin wall acoustic modelling using CFD technique. The acoustic absorptive properties measured by Kundt’s tube are used to determine porous coefficients and model acoustic absorption using acoustic wall treatment. Overall SPL is predicted at passenger ear level and also test measurements are done at same location in a semi anechoic chamber. CFD predictions shows good correlation with test measurements. Simulation process employed has provided detailed information on source strength, source location and ranking. FIND post processing has helped to pinpoint, quantify and rank noise sources. This feature helps to make quick decision on which part of the design needs to be changed to improve acoustic performance. Overall the process is found beneficial for HVAC noise prediction during vehicle development.