A method to separate wind-tunnel background noise and wind noise from interior measurements.

摘要

The interior noise in an automobile is extremely important to its salability. High acoustic levels can be extremely annoying and can cause driver fatigue. Because of this, the design on automobiles with low interior noise is becoming a high priority for automobile manufacturers. As the engine, tire and other noise sources are progressively being controlled, more effort is being placed in controlling the wind noise sources. In order to control these noise sources, wind tunnel testing of the vehicles is being performed with more emphasis on the interior acoustics. Unfortunately, most of the wind noise tests are being done in wind tunnels that were designed with little or no attention to their aeroacoustic characteristics. One concern then becomes how much of the measured interior noise is actually wind-tunnel background noise?; The present work presents a method where the contribution of the wind-tunnel background noise and the wind noise can be separated from the measured interior noise of an automobile. The method require cross-power or coherence measurements between a set of three transducers. The method was validated by examining the ability of the technique to educe a known background noise source (speaker) from the measured interior noise of a quarter cutout automobile in a wind tunnel lined with sound-absorbing foam. Additional tests were performed in a large hard-walled wind tunnel with production vehicles. It was found that reverberation was significant enough to affect the coherence measurements and thus the ability of the technique to educe the background noise. Numerous tests were done in a reverberation chamber to further study the reverberation effects on coherence measurements. An empirical method to account for reverberation was developed, which worked well for the cases examined in this work. Transducers other than microphones can also be used to educe the wind-tunnel background noise from and interior noise measurement. Accelerometers were used as two of the measurement transducers. The technique was also found to work well for these configurations.