PIV ---Galilean Identification of Large Scale Coherent Motions in a Shear Layer

1,000 PIV realizations were processed in a Galilean reference frame image of the shear layer's velocity field. Images with at least one node were processed as a collapsed sphere with four holes (Foss (2004) and (2007)). A square domain of side L, surrounding the node-center, was evaluated for its circulation: Gamma(L). The size of the ``large Scale Coherent Motion (LSCM)'' was defined as the maximum value of $<$omega$>$ where $<$omega$>$ = Gamma(L)/L**2. Lm designates the domain size for the maximum $<\omega >$ value. Statistical properties of the LSCMs include their sizes [Lm/theta(x)], strengths [$<$omega m$>$Lm/Uo], their position and their probability of occurrence within the observation window. These LSCMs are ``rare events'' as shown by their $<$omega m$>$/(uniformly distributed vorticity) = $\sim $ 100. The LSCMs may be related to the anomalous omega z (t) traces seen in direct vorticity measurements. J.F. Foss (2004) ``Surface Selections and Topological Constraint Evaluations for Flow Field Analyses,'' \textit{Experiments in Fluids}, Springer-Verlag, \textbf{37}, pp. 883-898. J. Foss, \textit{Springer Handbook of Experimental Fluid Mechanics}, Chapter C.13, Springer-Verlag, Berlin, 2007.