Synthetic Jet (SJ) actuators have emerged as efficient flow control tools for thermal and aerodynamic applications. The alternation of fluid ejection and suction from a circular or rectangular orifice produces a train of discrete vortical structures, which break down to form a zero-net-mass-flux jet stream. In most applications, SJs operate in the turbulent regime to maximize fluid mixing and heat/momentum trans- fers. For high-aspect-ratio rectangular jets, previous studies observed that the flow transition is initiated by three-dimensional instabilities [1], leading to the formation of spanwise-regular, rib-like structures around the core of the primary vortices at the beginning of the suction phase (as shown in figure 1, left). These distorted structures undergo cellular breakdown and generate small-scale turbulence. In this work, we aim to provide insights into the physical mechanisms leading to SJ formation using direct numerical simulations. A large spanwise-periodic domain, similar to the one used in [2] (fig. 1, right), is used to identify three-dimensional structures while eliminating spanwise end effects. Information on those coherent structures is obtained by data-driven modal analyses. It is shown that, during the suction phase, flow detachment in the slot and the cavity results in the formation of turbulent structures over a wide range of spanwise wavelengths. These vortices fill the whole actuator and are advected outside of it during the subsequent expulsion phase, thereby triggering primary vortex break- up. The analysis emphasizes the prominent role of velocity fluctuations in the cavity on the SJ transition, in conjunction with detached shear layer instabilities within the actuator during the suction phase. [1] B.L. Smith and A. Glezer. The formation and evolution of synthetic jets. Physics of Fluids, 10(9):2281–2297, 1998. [2] F. Capuano, A. Palumbo, and L. de Luca. Comparative study of spectral-element and finite-volume solvers for direct numerical simulation of synthetic jets. Computers & Fluids, 179:228–237, 2019.
Transition to turbulence in planar synthetic jets: numerical simulations and coherent structures eduction / Palumbo, A., Semeraro, O., De Luca, L.. - (2025), pp. 1-1. (Euromech Colloquium 658: Coherent structures and instabilities in transitional and turbulent wall-bounded flows Bari; Italy ).
Transition to turbulence in planar synthetic jets: numerical simulations and coherent structures eduction
Andrea Palumbo
Primo
;
2025
Abstract
Synthetic Jet (SJ) actuators have emerged as efficient flow control tools for thermal and aerodynamic applications. The alternation of fluid ejection and suction from a circular or rectangular orifice produces a train of discrete vortical structures, which break down to form a zero-net-mass-flux jet stream. In most applications, SJs operate in the turbulent regime to maximize fluid mixing and heat/momentum trans- fers. For high-aspect-ratio rectangular jets, previous studies observed that the flow transition is initiated by three-dimensional instabilities [1], leading to the formation of spanwise-regular, rib-like structures around the core of the primary vortices at the beginning of the suction phase (as shown in figure 1, left). These distorted structures undergo cellular breakdown and generate small-scale turbulence. In this work, we aim to provide insights into the physical mechanisms leading to SJ formation using direct numerical simulations. A large spanwise-periodic domain, similar to the one used in [2] (fig. 1, right), is used to identify three-dimensional structures while eliminating spanwise end effects. Information on those coherent structures is obtained by data-driven modal analyses. It is shown that, during the suction phase, flow detachment in the slot and the cavity results in the formation of turbulent structures over a wide range of spanwise wavelengths. These vortices fill the whole actuator and are advected outside of it during the subsequent expulsion phase, thereby triggering primary vortex break- up. The analysis emphasizes the prominent role of velocity fluctuations in the cavity on the SJ transition, in conjunction with detached shear layer instabilities within the actuator during the suction phase. [1] B.L. Smith and A. Glezer. The formation and evolution of synthetic jets. Physics of Fluids, 10(9):2281–2297, 1998. [2] F. Capuano, A. Palumbo, and L. de Luca. Comparative study of spectral-element and finite-volume solvers for direct numerical simulation of synthetic jets. Computers & Fluids, 179:228–237, 2019.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
