Fluid Dynamics Behind a Circular Cylinder Embedded With an Active Flapping Jet Actuator

The effects of an active flapping jet actuator on the wake flow dynamics behind a circular cylinder in wind tunnel tests were investigated. An active flapping jet actuator was embedded in the cylinder in advance to invoke a spontaneous flapping jet into the cylinder's wake. The experiment, which was performed in a wind tunnel with a Reynolds number of Re = 1.99 × 10⁴, was based on the oncoming wind speed, cylinder diameter, and kinematic viscosity of the air at the laboratory's temperature. The flow-field structures behind the cylinder model with different dimensionless jet momentum coefficients, C_u, were obtained using the high-speed particle image velocimetry technique. The proper orthogonal decomposition (POD) method was used to represent the variation of the POD mode energy, mode coefficients, and the reconstructed spreading vorticity. The dynamic temporal evolution and time-averaged results in the near wake region of the cylinder with and without active flapping-jet control were calculated and analyzed to illustrate the rich phenomena produced by, and the control effect of, the flapping jet. For C_u values up to 0.0554, the periodic vortex shedding was pushed to farther wakes. Meanwhile, the time-averaged wake changed considerably, and the distributions of the turbulent kinetic energy and Reynolds shear stress decreased significantly. A data-driven dynamic mode decomposition method was used to extract the coherent structure of the wake of the cylinder embedded with the flapping jet actuator. The Strouhal number of the main mode of the C_u = 0.0865 case was different from the natural case.