Detection of Coherent Structures in LDV Data Using Combined Visualization in Square Duct Flow
Near-wall streaky structures have been studied in a fully-developed turbulent square-duct flow by using combined dye flow visualization — LDV velocity measurement techniques. The velocity fluctuations are conditioned on the topological properties, such as coalescing and branching, and the transverse locations of the visually-identified low-speed streaks. It is shown that a symmetric pair of counter-rotating quasi-streamwise vortices is associated with one low-speed streak in a statistical sense. However, upstream of coalescing point and downstream of branching point of the low-speed streaks, a single quasi-streamwise vortex is associated with one low-speed streak.
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