Flow Patterns of Self-Sustained Oscillations in Fluidic Diverters

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Flow Patterns of Self-Sustained Oscillations in Fluidic Diverters

Fromm, Matthias / Kim, Jeonglae / Seifert, Avraham / Kriegseis, Jochen / Grundmann, Sven

A fluidic oscillator is a device capable of transforming a steady input flow into an oscillatory output using solely fluid dynamic principles and without requiring any moving components. Although the basic operation principles of fluidic oscillator are known to some extent, the unsteady and turbulent nature of its internal flow remains difficult to understand. The current study aims to further clarify the complicated flow physics involved in fluidic oscillators by investigating a device based on the fluid diverter principle. Spatiotemporally resolved velocity and pressure data obtained from a large-eddy simulation of the internal flow are decomposed into the proper orthogonal modes. The finite-time Lyapunov exponents are computed on the flowfield reconstructed using the proper orthogonal modes to perform a Lagrangian analysis of the switching mechanism. It is found that four dominant modes are sufficient to describe the jet switching. Strong coherent structures are found to separate the flow going through the oscillator from secondary flows through the feedback tube. The deflection of the jet inside the device is found to depend only on the pressure difference across the control ports, whereas the change of this pressure difference is mediated by the flows in the feedback tube.