THREE-DIMENSIONAL WAKES: ORIGIN AND EVOLUTION

Efforts made around 1930 for establishing a theoretical model of the wake shed by axisymmetrical bluff bodies at low Reynolds numbers failed because of inadequate information concerning the actual characteristics of the trail. In fact, not until 30 yr later were these characteristics ascertained by Magarvey and Bishop. They determined that the wake pattern changes, as the Reynolds number increases, from a single thread to a double thread, at first straight and then wavy, and eventually to a procession of vortex loops. By accepting the hypothesis (supported by experimental evidence) that the double thread consists of a pair of counterrotating eddy filaments, a model is presented that reproduces the indicated evolution and permits the computation of the main wake characteristics. An account is given of experiments performed for testing the accuracy of the model.