Shepherd's whistle
They are also produced commercially. Simple whistles may cost less than 1 USD in bulk; expensive ones may be quite ornate. They are commonly made of plastic, aluminum, stainless steel, silver, brass, titanium, Corian, jade, buffalo horn and other materials.
Physics of whistles
The Strouhal number
was used as the scaling factor. The highest frequency (7554 Hz) was found in the “overblown” condition and "n" was presumed as one corrugation. At the least flow rate, the frequency of 2452 Hz compared favorably to "n" = 3. At intermediate flow rates, several non-harmonically related frequencies occurred simultaneously suggesting that several corrugations were involved in the sound generation. In the smaller metal tube, a predominant tone appeared at 6174 Hz and corresponded to "n" = 2. A unique aspect of this whistle is that the internal flow carries both the unstable vortex downstream and the returning feedback signal upstream.