Acoustic Synthesis of an Automotive HVAC

A1 - CEVAS Project (HVAC of cars)

The acoustic synthesis is a design and/or diagnosis approach used to analyze and predict the acoustic behavior of a complex system. Based on the components found in the system, an acoustic pattern is implemented in which the acoustic sources and pathways from the source to the reception point are identified. At this point of reception a performance criterion is usually assigned that has to be optimized (sound pressure level, sound power level, psychoacoustic criterion ...). The acoustic synthesis provides a conception tool to the designer to predict the noise produced by a system considering the chosen components and the operating conditions.
In this paper, an acoustic synthesis is performed on an automotive HVAC considering operating conditions. Based on the requirements of a sound synthesis in terms of time spent, accuracy and outcomes, one will present a synthesis of a simplified model using experimental results, empiric laws and theoretical approach. The final result is the sum of the contributions of each sources modified by the transfer functions (transmission losses) of pathways encountered.
The synthesis is developed in order to propose an approach which take into account the integration effects and some interaction effects. In this case, the pathways are represented by diffusion elements and the sources by volumetric strength. In an automotive HVAC, the fan is the most important source while the flaps and heat exchangers are weaker sources and mainly diffusion elements.
The integration effects are due to the acoustic cavity in which is located a source. The interaction effects are, for instance, the change of the operating point due to a variation of flap opening or the effects on a flap of turbulent flow created by an uphill component.
This work has been developed in the FUI project called Cevas