Modal Analysis of a Sweeping Jet Emitted by a Fluidic Oscillator
Daniel J. Portillo, Eugene N. Hoffman, Matt Garcia, Elijah J. LaLonde, Emilio Hernandez, Christopher S. Combs, Lyle Hood
Abstract
View Video Presentation: https://doi.org/10.2514/6.2021-2835.vid Recent experimental and computational evaluations of fluidic oscillators, or sweeping jet actuators, have demonstrated their usefulness across a variety of aerospace applications. One of the most commonly used fluidic oscillator geometries—the Bray geometry—produces a highly turbulent flow at its outlet and provides tunability through geometric scaling. However, while that design has been adapted for various applications, specific flow structures within the sweeping jet have not been coupled with its performance scalability. Addressing this knowledge gap was the objective of this manuscript, which characterized fluidic oscillator performance across various length scales. Specifically, this study focused on experimentally evaluating the oscillation frequencies, oscillation angles, and mode structures across different length scales of a fluidic oscillator. Five different length scales of a single fluidic oscillator geometry were 3D printed and high-speed Schlieren imaging was used to visualize various flow rates of air exiting the fluidic oscillators. Custom MATLAB algorithms were used to determine the oscillation frequencies and angles, as well as modal structures, from those images. The modal analysis consisted of proper orthogonal decomposition (POD) and a spectral-kernel-based POD. The results showed that the oscillation frequency is directly proportional to the flow rate and inversely proportional to the scaling size. The results also showed that the oscillation angle is inversely proportional to the flow rate and directly proportional to the scaling size. The modal analysis showed that the mode structures complied with the oscillation frequencies and oscillation angles.