Fluidic Oscillators, the Effect of Some Design Modifications

Abstract

The number of applications where fluidic oscillators are expected to be used in the future, is raising sharply, then their ability of interacting with the boundary layer to modify forces on bluff bodies, enhancing heat transfer or decreasing noise generation, are just few of the applications where fluidic oscillators can be used. For each application a particular pulsating frequency and amplitude are required to minimize/maximize the variable under study, force, Nusselt number, etc. For a given range of Reynolds numbers, fluidic oscillators present a linear relationship between the output frequency and the incoming fluid flow, yet it appears the modification of the internal fluidic oscillator geometry may affect this relation. In the present paper and for a given fluidic oscillator, several performance parameters will be numerically evaluated as a function of different internal modifications via using 3D-CFD simulations. The paper is also evaluating the relation between the momentum applied to the mixing chamber incoming jet and the oscillator output characteristics. The evaluation is based on studying the output mass flow frequency and amplitude whenever several internal geometry parameters are modified. The geometry modifications considered were: the mixing chamber inlet and outlet widths, and the mixing chamber inlet and outlet wall inclination angles. The concept behind this paper is, to evaluate how much the fluidic oscillator internal dimensions affect the device main characteristics, and to analyze which parts of the oscillator produce a higher impact on the fluidic oscillator output characteristics. For the different internal modifications evaluated, special care is taken in studying the forces required to flip the jet. The entire study is performed for three different Reynolds numbers, 8711, 16034 and 32068. Among the conclusions reached it is to be highlighted that, for a given Reynolds number, modifying the internal shape affects the oscillation frequencies and amplitudes. Any oscillator internal modification generates a much relevant effect as Reynolds number increases. Under all conditions studied, it was observed the fluidic oscillator is pressure driven.

Fluidic Oscillators, Feedback Channel Effect under Compressible Flow Conditions

“…When studding the same FO configuration under incompressible flow conditions and at Reynolds numbers up to 32,000, refs. [ 39 , 41 ] established that flow oscillations were driven by the alternating pressure variation at the FC’s outlets. Based on the results presented in this sub section, the required force responsible for driving the jet oscillations inside the MC appears to be generated by the pressure difference at the FC’s outlets.…”

“…Another important point to clarify is which of the two terms characterizing the net momentum acting onto the jet is the dominant one. In a previous numerical work done by Baghaei and Bergada [ 39 , 41 ], using the same oscillator configuration but under incompressible flow conditions, water was used as working fluid, it was stated that the net-momentum pressure term, see Equations (1) and (2), was the dominating one and therefore was responsible for the main jet oscillations. Under compressible flow conditions, Figure 14 compares for the baseline case and the maximum FC length L9, the net-momentum mass flow term with the net-momentum pressure term measured at the FC outlets.…”

Computational Fluid Dynamics (CFD) Simulation of Mesh Jet Devices for Promising Energy-Saving Technologies

“…A summary of the scientific research results performed in 2020 and 2022 [1][2][3][4][5][6][55][56][57][58][59] makes it possible to state the following:…”

Aerodynamic Efficiency Improvement on a NACA-8412 Airfoil via Active Flow Control Implementation

“…(3) Fluidic actuators (FA), create pulsating flow and in some configurations no moving parts are required. In some particular FA designs, the origin of the self-sustained oscillations was recently unveiled in [15][16][17].…”