In some special situations the wind-induced noise of perforated plates may show strong power enhancement in a certain frequency band and hence exhibits a "tone-like" character. This problem is investigated experimentally in laboratory and some test results are presented in this paper. It is shown that the "tone-like" phenomenon happens only when the incident angle of the wind is relatively large to the perforated panel; say between 60 and 80 degrees. There seems an "optimum" wind speed corresponding to the size of the holes for this phenomenon. The peak frequency of the tone-like signal is mainly determined by the thickness of the plate and the size of the holes and can be roughly estimated from the geometry of the plate and the wind speed. The condition when the tone-like phenomenon may happen seems very much dependent on the perforation pattern along the wind direction. Same perforated plate may produce totally different sound in the same wind condition if the orientation of the plate is changed. Randomized hole size and distribution may help to reduce the tone-like signal and hence the total wind-induced noise. Possible explanations of the phenomenon are discussed.
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