The standard method for preventing a heat exchanger from generating a loud noise is to insert acoustic baffles which subdivide the vessel. It had previously been thought that such baffles would increase the acoustic natural frequency and thus prevent a resonance condition involving interactions between the sound field and wake oscillations behind tubes. Theoretical and experimental investigations, described in this paper, show that the effect of introducing an acoustic baffle into a shell is to decrease the acoustic natural frequency. This effect is not helpful and may result in resonant conditions being more common. However, an additional effect of an acoustic baffle is to change the direction of the acoustic waves and thus prevent good spatial correlation between wake oscillations and the sound field. It is this latter effect which makes acoustic baffles effective. Hence, spatial correlation should be made the basis of any design method.
Spatial Diversity and Spatial Correlation Evaluation of Measured Vehicle-to-Vehicle Radio Channels at 5.2 GHz
