On the three-dimensional flow evolution of a submerged synthetic jet with two circular orifices

Synthetic jet has shown promising applications in active flow control in recent years. Tomographic particle image velocity (Tomo-PIV) is an emerging flow field measurement, which can obtain three-dimensional flow field with a high spatial and temporal resolution to help us better understand the evolution of synthetic jet. Therefore, this paper uses a time-resolved Tomo-PIV system to measure and analyze the three-dimensional flow evolution of a submerged two-orifice synthetic jet. The measurement is conducted for stroke length L = 1.9, 2.6, and 3.0 while keeping the orifice diameter D and the distance between the two orifices s constant. Research results reveal that the three-dimensional flow evolution can be described as follows: first, two independent vortex rings form at the outlet of the orifice plate; next, these two vortex rings interact with each other and merge into a non-circular vortex ring, which then undergoes axis switching and vortex reconnection, with the tendency of splitting into two vortex rings. Furthermore, the position where the axis-switching finishes coincides with the location of the maximum mean streamwise velocity. When the stroke length of the synthetic jet is 2.6, the non-circular vortex ring undergoes a collision of vortices after the completion of the axis switching, resulting in the phenomenon of vortex ring bifurcation. However, the non-circular vortex ring fails to split into two vortex rings for stroke lengths of 1.9 and 3. Moreover, the entrainment of the synthetic jet increases with the increase in stroke length.