Vortex shedding from finned tubes

The frequency of regular vortex shedding from a finned tube of the kind used in heat exchangers has been measured for an isolated tube in a wind tunnel. A Strouhal number expressed in terms of an effective diameter, defined as the frontal area per unit length of tube, is found to be nearly constant and to depend only on the ratio of fin spacing to tube diameter. The addition of fins to a tube increases the sharpness of the peak in the power spectrum obtained from a hot-wire anemometer.