Aeroacoustic Characteristics of Automotive HVAC Systems

A systematic method is developed to investigate the noise generated by automotive HVAC systems. Noise measurements are performed on the front and rear HVAC systems of an automobile to illustrate the use of the developed method and to show that it is capable of identifying various noise sources and the relative importance of each source. The method entails measurements of the total sound power radiated by the HVAC system, the sound power generated by the fan alone as well as the use of a loudspeaker to replace the fan impeller and measure the transmission loss of the HVAC ducts with and without flow. It is shown that different noise sources dominate over different frequency ranges. At low frequencies, the noise generated by flow in the HVAC ducts dominates. However, in the high frequency range, f > 500 Hz, the duct flow noise and the fan noise are both important.