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

近年来，流体振荡器发射的空间振荡射流在流动控制中的有效应用得到了令人印象深刻的证明。这种功效伴随着流体振荡器的优点，它不需要任何运动部件来产生空间振荡射流。然而，空间振荡射流优越性能的驱动机制仍然未知。然而，这些信息对于应用程序的基本理解和适当的优化过程至关重要。该流场的三维性和非定常性，加上高振荡频率和高振荡速度，使得实验和数值研究具有挑战性。在以往的研究中，研究人员对空间振荡射流的基本流场进行了研究，并揭示了一些流动特征，这些特征有希望成为流控性能优越的驱动机制的一部分。然而，对于流量控制应用来说，几个特别重要的问题仍然没有解决。在本研究中，通过研究先前确定的最关键参数对相互作用的多个振荡射流流场的影响来解决这些问题。感兴趣的参数是斯特劳哈尔数，射流和横流之间的速度比，以及相邻振子之间的相位同步。预计这些参数的不同组合将产生具有不同流动控制机制的通用流场。一个简单的分离控制场景用于验证参数组合的有效性，并用于量化单个流特征对分离控制有效性的贡献。在实验中，一组流体振荡器被放置在风洞中。振荡射流在特定频率和相位关系下随机或被迫振荡。三维，时间分辨的流场研究使用可穿越的立体粒子图像测速系统，结合已建立的相位平均技术和数据分析方法。此外，还进行了壁面压力测量，以量化空间振荡射流在分离控制中的有效性。研究结果将揭示空间振荡射流在分离控制中优越性能背后的驱动机制。此外，还将识别和量化最关键的流动特征及其对分离控制效果的影响。该研究的基本性质允许将结果转移到流量控制应用程序。因此，研究结果将作为应用优化、数值计算验证以及未来研究附加参数影响的基础。

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.