Coherent structures in turbulent shear flows: The confluence of experimental and numerical approaches

Physics based low dimensional approaches are playing an increasingly important role in our understanding of turbulent flows. They provide an avenue for us to understand the connection between coherent structures and the overall dynamics of the flow field. As such these approaches are fundamental to the implementation of physics based active control methodologies. In this paper we review applications to various low dimensional approaches (including Proper Orthogonal Decomposition (POD), Linear Stochastic Estimation (LSE), Conditional Averages and Wavelets) to turbulent shear layers and connect the results to simulation tools. The applications of all these methods to the 2D shear layer suggest a kind of universal behavior of both the large scale structure extracted and the background turbulence, irrespective of the technique (filtering method) used. A review of the application of POD and LSE to the axisymmetric jet at Reynolds number between 10,000 and 800,000 and Mach numbers ranging from very low to 0.6 suggest a universal behavior where the dynamics can be described with relatively low dimensional information (1 POD mode and 5 or 6 Fourier azimuthal modes) over the Reynolds/Mach number range studied. These results provide physical justification for simulation tools such as VLES, LES and SDM since such computational methods involve different levels of low-dimensional modeling.