Synthetic jet actuators (SJAs) is a promising flow control device for a wide range of engineering applications (e.g., in aerodynamics control) because of its unique tributes. The traditional SJAs employ the dynamic oscillation of a rigid active surface within an open cavity to impart momentum flux through the orifice opening of the cavity with zero mass flux. A train of isolated vortex rings are created, as shown in the video and flow pathline visualization in panel (A). The resultant synthetic jet, as a secondary flow, however, suffers from critical limitations such as low efficiency in momentum injection. Recently, we discovered that the employment of a compliant active surface (such as a thin elastic membrane) could induce special synthetic jets (shown in panel (B)) with significantly enhanced momentum injection efficiency. Some of the natural oscillation modes of the compliant surface excited by actuations at certain frequencies result in an enhanced vorticity generation and accumulation mechanism.  We focus on understanding the physics and optimal actuation conditions for compliant surface-based SJAs, and developing coordinated spatio-temporal actuation strategies to exploit the synergetic effects of multiple distributed actuators. This fundamental research sheds light on the development of next generation flow control actuators with enhanced capability and expanded application range.  

References

1. Skinder Dar, Chukwudum Eluchie, Cong Wang, (2026) “Experimental Characterization of Duty Cycle Modulation in Square-Wave Synthetic Jet Actuators”, Physics of Fluids, DOI: 10.1063/5.0309807
2. Chukwudum Eluchie, Skinder Dar, Cong Wang. (2025). Development of a novel synthetic jet using a deformable dynamic surface. Physics of Fluids, 37(12).
3. Cong Wang, Morteza Gharib. (2022). Physics of a strongly oscillating axisymmetric air-water interface with a fixed boundary condition. Physical Review Fluids, 7(4), 044003.
4. Video entry to the Gallery of Fluid Motion of the 73th APS DFD meeting 2020

Video Entry of 73th Gallery of fluid motion

Turbulent boundary layers (TBLs) that form over the surface of moving transportation systems (e.g., airplanes and containerships) exerts tremendous shear stress and drag force, which accounts for 50% to 80% of the total energy expenditure. While many promising drag reduction techniques have been developed, sustainably reducing turbulent drag remains a fundamental challenge. The approach of employing a non-canonical deformable boundary offers a promising scalable solution. Our recent research demonstrates that the coherent structures and Reynolds shear stress of TBLs can be drastically modified by a deformable boundary surface [1,2]. Through actuating an array of the deformable surface boundary based actuator (shown in Research Direction I), up to 45% drag reduction was achieved [3]. It was further discovered that the coupled TBL/deformable boundary interactions result in stabilized turbulent vortices [4] and a local re-laminarization process [5]. In the next step, we will systematically characterize TBLs near the wall boundary with or without deformable boundary. in addition, we will implement coordinated spatio-temporal actuation of distributed surface actuators (e.g., to mimic transpiration traveling waves along the wall boundary) to maximize the drag reduction effect. Our research work was featured on the front cover of Journal of Fluid Mechanics [3]. 

References

1. Minh Nguyen, Cong Wang, (2026) “Dynamic free-slip effects of patterned superhydrophobic surfaces on transition turbulent boundary layers”, AIAA Journal, accepted 
2. Minh Nguyen, Mohammad Mohammadzadeh, Ikram Haider, Hongtao Ding, Cong Wang, (2026) “Hybrid turbulent drag reduction via interactions of deformable air films and injected air-bubbles over super-hydrophobic surfaces”, under review, Experimental Thermal and Fluid Science
3. Wang, C., & Gharib, M. (2020). Effect of the dynamic slip boundary condition on the near-wall turbulent boundary layer. Journal of Fluid Mechanics, 901, A11.
4. Wang, C., & Gharib, M. (2022). On the Turbulent Drag Reduction Effect of the Dynamic Free-Slip Surface Method. Journal of Marine Science and Engineering, 10(7), 879.
5. Wang, C., & Gharib, M. (2021). Local relaminarization mechanism induced by a dynamic free-slip boundary. Physical Review Fluids, 6(8), 084604.