3-DIMENSIONAL INSTABILITIES IN THE WAKE OF A CIRCULAR-CYLINDER

The two- and three-dimensional wake structure behind a circular cylind er has been computed using a high-order spectral element technique. Fo r the two-dimensional computations the predictions are compared with a ccurate experimental results and agree to within experimental uncertai nty for the Strouhal number and base pressure coefficient. For the thr ee-dimensional simulations, the two modes of three-dimensional instabi lity, designated as modes A and B, both found experimentally but not p reviously computationally, have been captured. Mode A appears first at a Reynolds number slightly less than 200. As the Reynolds number is i ncreased, there is a transfer of energy to mode B, which has a wavelen gth approximately one-fourth that of mode A.