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COHERENT VORTICAL AND STRAINING STRUCTURES IN THE FINITE WALL-MOUNTED SQUARE CYLINDER WAKE

J. A. Bourgeois
Deptartment of Mechanical and Manufacturing Engineering University of Calgary 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada

P. Sattari
Deptartment of Mechanical and Manufacturing Engineering University of Calgary 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada

Robert J. Martinuzzi
Department of Mechanical and Manufacturing Engineering Schulich School of Engineering, University of Calgary 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4

Аннотация

Topological aspects of the turbulent wake of a finite, surface-mounted, square-cross-section cylinder of h/d = 4 are addressed by decomposing the velocity field into a quasi-periodic coherent part and deviations therefrom as unresolved incoherent fluctuations. The three-dimensional large scale structure is educed through a reconstruction of phase-averaged PIV x-y and x-z measurement planes using the simultaneously sampled surface pressure difference on either side of the obstacle as a phase reference. A topological model for the vortex structure is educed and an explanation for mean streamwise wake vorticity is given in terms of the connections between initially vertical structures shed alternately from either side of the obstacle, rather than 'tip' vortex structures generated at the obstacle free-end as proposed in other studies. The coherent structure educed accounts for a significant portion of the fluctuating energy in the wake. The turbulent field is analyzed by finding Lagrangian straining structures that form by induction of the vorticity field, and these structures are related to the energy transfer from the base phase-averaged flow.