This paper reports on a series of large-eddy simulations of a round
jet issuing normally
into a crossflow. Simulations were performed at two jet-to-crossflow velocity
ratios,
2.0 and 3.3, and two Reynolds numbers, 1050 and 2100, based on crossflow
velocity
and jet diameter. Mean and turbulent statistics computed from the simulations
match experimental measurements reasonably well. Large-scale coherent structures
observed in experimental flow visualizations are reproduced by the simulations,
and
the mechanisms by which these structures form are described. The effects
of coherent
structures upon the evolution of mean velocities, resolved Reynolds stresses,
and
turbulent kinetic energy along the centreplane are discussed. In this paper,
the
ubiquitous far-field counter-rotating vortex pair is shown to originate
from a pair of
quasi-steady ‘hanging’ vortices. These vortices
form in the skewed mixing layer that
develops between jet and crossflow fluid on the lateral edges of the jet.
Axial flow
through the hanging vortex transports vortical 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 pressure gradient and breaks down. As this breakdown
occurs,
the vortex diameter expands dramatically, and a weak counter-rotating vortex
pair is
formed that is aligned with the jet trajectory.
Characterizing the coherent structures in large eddy simulations of aligned windfarms
