Experimental Study of Novel Synthetic Jets Induced by Dynamic Deformable Surfaces

Synthetic jets (SJs), as a promising approach to active flow control, are typically generated by the dynamic oscillation of rigid surfaces within a surface cavity through unsteady flow separation at the cavity orifice. SJs can be induced by the oscillation of dynamically deformable surfaces (DDS) without the need of unsteady flow separation, which possess unique fluid dynamic characters for flow control purposes. This study investigates the effects of two different DDS designs, including a free-slip air–water interface (referred as interface DDS) and a thin deformable elastic membrane (referred as membrane DDS) on the performance characteristics of DDS-based SJs. The two configurations are systematically compared, with pressurized air and water selected as the working fluid within the cavity, respectively. Time-resolved 2D Particle Image Velocimetry (PIV) and qualitative flow visualizations were employed to demonstrate the physics of these two DDS-based SJs. Flow pathline visualizations reveal that the interface DDS deforms more readily than the membrane DDS with a lower actuation power, which results in more energy-efficient jets. The phase-averaged velocity in the near-field of DDS for both configurations exhibit distinct oscillation modes, with characteristics resembling Bessel-type oscillations; notably, oscillations involving stronger curvature deformations result in higher centerline velocities and stronger jet vorticity. The dimensionless stroke length (L_0/D_0 ) of DDS-SJs was much lower than the conventional SJs, indicating a reduced excitation threshold and a departure from the established SJ scaling laws. These findings provide deeper insights into the dynamics of DDS-SJs and underscore their potential for cross-disciplinary applications, such as turbulence control and biomimetic propulsion. While the interface-based actuator is less suitable for submerged applications, it offers advantages in surface flow control. The membrane-based actuator, with its durability and tunable response, shows promise for underwater propulsion, turbulent drag reduction, and adaptive flow devices.