# Computational Characterization of Turbulent Flow in a Microfluidic Actuator  
[PERSON]  
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[PERSON] and [PERSON]  
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Footnote 1: email: {[PERSON]; [PERSON], [PERSON]; [PERSON]  
materials, applications and mechanisms. [PERSON] et al. [3] have made an elaborated description of the functioning of a fluidic oscillator device. In recent years, there has been a flurry of activity both in the design of new fluidic oscillators and new applications. Fluidic oscillators have found novel applications in the flow control of swirl flame dynamics [4], fuel combustion in gas turbines [5], control of fluid flow for aerodynamics applications [6], ultrasonic testing [7], jet actuators for flow control [8], fuel injection in hydrogen engines [9], even in controlling the flow in fume cupboards in chemistry laboratories [10]. One very interesting application is that presented in [11], where a fluidic oscillator was coupled with a low-temperature plasma dielectric barrier discharge device to produce ozone-rich microbubbles as a cost-effective means to lyse cyanobacterial cells and degrade the cyanotoxins they produce. The use of microbubbles is advantageous as heat and mass transfer are enhanced as the size of the bubbles is decreased; in addition, the use of ozone produced in a microplasma has energy, capital investment and maintenance cost savings that make the use of advanced oxidation technologies more attractive for water treatment. [PERSON] and [PERSON] [12] established the kinetic conditions under which ozone can be cheaply and efficiently produced in a microplasma, and [PERSON] [13] made an extensive review of the state of the art in fluidic oscillators for microbubble generation. The fluidic oscillator considered in this work is that studied experimentally in [PERSON] et al. [14] and numerically in [PERSON] et al. [15]. This device consists of an inlet nozzle, also known as a power nozzle, which injects a liquid (water) into a mixing chamber--also known as an interacting region. It has two feedback loops that link the rear part of the mixing chamber with its front part, and an outlet port connected to two expanding branches with outlets exposed to ambient pressure (see Figure 1 below), through which the oscillating flow leaves the device. The experiments employed planar particle image velocimetry (PIV) to obtain time-resolved velocity fields of the fluid inside the actuator. From the numerical point of view, the commercial software ANSYS-CFX was used to perform URANS (Unsteady Reynolds Averaged Navier-Stokes) simulations aimed at describing the turbulent flow time evolution. Comparison of the two-dimensional (2D) computed and measured contour velocity fields was satisfactory; moreover, the smallest difference between the numerical and experimental operational frequency of the fluid oscillator was found when the \(\mathrm{k}-\omega\) Shear Stress Transport (SST) turbulence model was applied. Therefore, the authors conclude that 2D computations are sufficient to capture the principal features of the flow inside the oscillator. More recently, [PERSON] et al. [16] performed three-dimensional simulations of the turbulent flow in the previous oscillator. That study focused on the evaluation of a few geometric modifications aimed at altering the oscillator's operating frequency. They used a hybrid Detached Eddy Simulation (DES) turbulence model in OpenFoam, which is an open CFD software, to simulate the flow characteristics. The width of the inlet and exit sections of the mixing chamber as well as the angles of the inner walls of the exit nozzle were modified, and curves of frequency and amplitude of the oscillation versus the  
Figure 1: Computational domain of the fluidic oscillator in [14] illustrating its parts as well as the boundary conditions. corresponding dimension values were produced. It was shown that the frequency can be increased by augmenting the width of the exit section, whereas the opposite effect was found when it was reduced.