Large-eddy Simulations on Flow Structures and Interaction Mechanism of Synthetic Jets in a Crossflow

The results of large-eddy simulations are presented to illustrate the flow structures generated by the interaction of synthetic jets with a crossflow. The coupled calculations involving the internal flow of the actuator cavity and the external flow are performed using the ANSYS-Fluent software. The influence of the orifice shape (round orifice and rectangular orifices with aspect ratio of 6, 12, or 18) on the evolution of coherent structures is analyzed, and the effects of the jet-to-crossflow velocity ratio (0.5, 1.0, or 1.5) on the turbulent flow behavior are examined. The results show that the first vortex ring shed from the rectangular orifice lip behaves as a plate-like vortex. The horseshoe vortex and first vortex ring are followed by a trailing jet in the case of a round orifice, but this configuration is rarely identified when the orifice is rectangular. For the rectangular orifice with an aspect ratio of 18, the plate-like vortex splits into vortex filaments that become interwoven with the center of the synthetic jet. In general, at the same characteristic velocity, the round-orifice synthetic jet has a stronger capacity for normal penetration into the crossflow, whereas the rectangular-orifice synthetic jet with a large aspect ratio develops closer to the wall. For the rectangular orifice with a large aspect ratio, the development of the synthetic jet is restricted to a small region near the wall at a small jet-to-crossflow velocity ratio.