Investigation of jet control using pulsed jets with three azimuthal modes

In this paper, a turbulent jet manipulated by pulsed control jets is investigated using large-eddy simulation. Four pulsed jets are arranged around the nozzle exit and work under three azimuthal modes; i.e., symmetric, flapping or first mixed and second mixed modes. Time-averaged statistics revealed that the shear layer exhibits different spreading rates along different azimuthal directions. In addition, the complexity of the generated coherent structures depends on the forcing method. Under the symmetric mode, the shear layer in the forced plane rolls up early, and the coherent structure is stretched along the downstream direction in the unforced plane, forming a distorted ring ultimately. Under the flapping mode, staggered vortex rings are formed when viewed from the forced plane. These structures introduce heavily oscillation of the primary jet in the near field, which eventually bifurcates. Under the second mixed mode, the single distorted vortex rings resemble those under the symmetric mode. However, the axes of neighboring rings are orthogonal to each other. Therefore, a strong mutual interaction occurs between neighboring rings. In particular, the front part of a ring is inhaled into its preceding counterpart. Meanwhile, the rear part of the preceding ring is pushed outward, resulting in a more distorted structure. The mode analysis suggests that the disturbance generated by the second mixed mode is sustained for longer distance in the flow field.