The Effect of Strouhal Number, Velocity Ratio and Phase Correlation on Separation Control with Spatially Oscillating Jets

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In recent years, the effective and efficient application of spatially oscillating jets emitted by fluidic oscillators for flow control has been impressively demonstrated. This efficacy is accompanied by the advantage of fluidic oscillators not requiring any moving parts for generating the spatially oscillating jet. Nevertheless, the driving mechanisms for the superior performance of spatially oscillating jets are still unknown. However, this information is crucial for a fundamental understanding and a proper optimization process for applications. The three-dimensionality and unsteadiness of this flow field in conjunction with high oscillation frequencies and velocities make experimental and numerical studies challenging. In previous studies, the fundamental flow field of a spatially oscillating jet was investigated and revealed some flow features that are promising candidates to be part of the driving mechanisms behind the superior performance in flow control. However, several questions that are of particular importance for flow control applications remained open. In this study, these questions are addressed by investigating the effect of the previously identified most crucial parameters on the flow field of multiple oscillating jets interacting with each other. The parameters of interest are the Strouhal number, the velocity ratio between jet and crossflow, and the phase-synchronization between adjacent oscillators. It is expected that different combinations of these parameters yield versatile flow fields with different flow control mechanisms. A simple separation control scenario is used for validating the effectiveness of the parameter combinations and for quantifying the contribution of the individual flow features to the separation control effectiveness.For the experiments, an array of fluidic oscillators is placed inside a wind tunnel. The oscillating jets oscillate randomly or forced at specific frequencies and phase-relations to each other. The three-dimensional, time-resolved flow fields are investigated using a traversable stereoscopic particle image velocimetry system in combination with established phase-averaging techniques and data analysis approaches. In addition, wall pressure measurements are conducted to quantify the effectiveness of the spatially oscillating jets in separation control.The results will reveal the driving mechanisms behind the superior performance of spatially oscillating jets in separation control. Furthermore, the most crucial flow features and their influence on the separation control effectiveness will be identified and quantified. The fundamental nature of the study allows transferring the results to flow control applications. Hence, the results of the study will serve as a basis for optimization in applications, validation of numerical calculations, and future studies inspecting the influence of additional parameters.