Large-eddy simulations of a round jet in crossflow

This paper reports on a series of large-eddy simulations of a round jet iss uing normally into a crossflow. Simulations were performed at two jet-to-cr ossflow velocity ratios, 2.0 and 3.3, and two Reynolds numbers, 1050 and 21 00, based on crossflow velocity and jet diameter. Mean and turbulent statis tics computed from the simulations match experimental measurements reasonab ly well. Large-scale coherent structures observed in experimental flow visu alizations are reproduced by the simulations, and the mechanisms by which t hese structures form are described. The effects of coherent structures upon the evolution of mean velocities, resolved Reynolds stresses, and turbulen t kinetic energy along the centreplane are discussed. In this paper, the ub iquitous far-field counter-rotating vortex pair is shown to originate from a pair of quasi-steady 'hanging' vortices. These vortices form in the skewe d mixing layer that develops between jet and crossflow fluid on the lateral edges of the jet. Axial flow through the hanging vortex transports vortica l fluid from the near-wall boundary layer of the incoming pipe flow to the back side of the jet. There, the hanging vortex encounters an adverse press ure gradient and breaks down. As this breakdown occurs, the vortex diameter expands dramatically, and a weak counter-rotating vortex pair is formed th at is aligned with the jet trajectory.