COLLABORATIVE TESTING OF EDDY STRUCTURE IDENTIFICATION METHODS IN FREE TURBULENT SHEAR FLOWS

The thrust of this paper is to validate, test and compare several Cohe rent Structure eduction methods utilizing the same data base. The flow chosen was that of an experimental study of a plane, incompressible, fully developed turbulent two-stream mixing layer. The mixing layer wa s chosen as the data base because it has been studied extensively from a coherent structures point of view. In addition, its characteristics (similarity, convection velocities, etc.) are well documented. There are also no wall effects so that comparisons between techniques are si mplified. The data was collected from hot wire rakes with good spatial resolution thus allowing the contributors to apply and test different structure eduction techniques. The techniques chosen for discussion a nd used here have found wide utilization over the past decade, and all hold forth the promise of extensive application in the future. These include: Conditional Sampling (Vorticity-based and other methods); Wav elets; Pattern Recognition Analysis; Proper Orthogonal Decomposition; Stochastic Estimation; Topological Concept-based methods; Full Field M ethods (e.g., pseudo flow visualization). All are illustrated by appli cation to the mixing layer data base, and comparisons made between the results. This common study has shown that direct comparisons between results of several methods are now possible. Good quantitive and quali tative agreement between the different methods have been observed as w ell as some differences noted. As an example, the size of the averaged structures computed from the various methods compare to within 6 perc ent.