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Dynamics of Flow-Field behind Backward-Facing Step in the Plane of Symmetry
Uruba, Václav
Dynamics of the flow-field behind a backward-facing step in a narrow channel is studied experimentally using time-resolved PIV technique in the measuring plane being the plane of symmetry in the streamwise direction. The channel width is 4 step heights, Reynolds number based on the step height was about 7 200. Instability of the free shear layer of Kelvin-Helmholtz type is observed. Dynamics of the flow is studied using the Bi-Orthogonal Decomposition (BOD) and Oscillation Pattern Decomposition (OPD) techniques. Typical time-mean structures of velocity statistics as well as dynamical structures are to be presented.
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Identification of coherence in turbulent flows by local correlations
Tesař, Václav ; Něnička, Václav
Coherent structures are not included in practically useful models of turbulence due to scarcity of data upon which the modelling could be based. The problem is indistinct, vague, and continuously varying boundary of each structure, making difficult even identification of its very existence. The introduced identification method operates with a pair of flow visualisation images, computing local correlation coefficients in sequentially interrogated small image parts. The coherence is revealed by high local values of the coefficient. There are two variants, a scalar and vector approaches. The method is shown applied to an experiment in which the structures play an important role.
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