Investigating mode competition and three-dimensional features from two-dimensional velocity fields in an open cavity flow by modal decompositions
Guéniat, Florimond and Pastur, Luc and Lusseyran, Francois (2014) Investigating mode competition and three-dimensional features from two-dimensional velocity fields in an open cavity flow by modal decompositions. Physics of Fluids, 26 (8). ISSN 1070-6631
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Abstract
Shear-layer driven open cavity flows are known to exhibit strong self-sustained oscillations of the shear-layer. Over some range of the control parameters, a competition between two modes of oscillations of the shear layer can occur. We apply both Proper Orthogonal Decomposition and Dynamic Mode Decomposition to experimental two-dimensional two-components time and spaced velocity fields of an incompressible open cavity flow, in a regime of mode competition. We show that, although proper orthogonal decomposition successes in identifying salient features of the flow, it fails at identifying the spatial coherent structures associated with dominant frequencies of the shear-layer oscillations. On the contrary, we show that, as dynamic mode decomposition is devoted to identify spatial coherent structures associated with clearly defined frequency channels, it is well suited for investigating coherentstructuresinintermittentregimes.Weconsiderthevelocitydivergencefield, inordertoidentifyspanwisecoherentfeaturesoftheflow.Finally,weshowthatboth coherent structures in the inner-flow and in the shear-layer exhibit strong spanwise velocitygradients,andarethereforethree-dimensional
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