VERY LARGE STRUCTURES IN PLANE TURBULENT COUETTE-FLOW

A direct numerical simulation was carried out of plane turbulent Couet te flow at a Reynolds number of 750, based on half the velocity differ ence between the walls and half the channel width Particular attention was paid to choosing a computational box that is large enough to acco mmodate even the largest scales of the turbulence. In the central regi on of the channel very large elongated structures were observed, in ac cordance with earlier findings. The study is focused on the properties of these structures, but is also aimed at obtaining accurate turbulen ce statistics. Terms in the energy budget were evaluated and discussed . Also, the limiting values of various quantities were determined and their relevance in high Reynolds number flows discussed. The large str uctures were shown to be very sensitive to an imposed system rotation. They could be essentially eliminated with a stabilizing system rotati on (around the spanwise axis) small enough for only minor damping of t he rest of the scales. Despite the fact that the large structures domi nate the appearance of the how held their energy content was shown to be relatively small, on the order of 10% of the total turbulent kineti c energy.