Print Email Facebook Twitter Three-dimensional evolution of flow structures in transitional circular and chevron jets Title Three-dimensional evolution of flow structures in transitional circular and chevron jets Author Violato, D. Scarano, F. Faculty Aerospace Engineering Department Aerodynamics & Wind Energy Date 2011-12-27 Abstract The three-dimensional behavior of flow transition in circular and 6-chevron jets at Re?=?5000 is investigated with experiments conducted on a free water jet by time-resolved tomographic particle image velocimetry. The emphasis is on the unsteady organization of coherent flow structures, which play a role in the generation of acoustic noise. Shedding and pairing of vortices are the most pronounced phenomena observed in the near field of the circular jet. The first and second pairing amplify the axial pulsatile motion in the jet column and lead to the growth of azimuthal waves culminating in the breakup of the vortex ring. Streamwise vortices of axial and radial vorticity are observed in the outer region and move inward and outward under the effect of the vortex rings. In the jet with chevrons, the axisymmetric ring-like coherence of the circular jet is not encountered. Instead, streamwise flow structures of azimuthal vorticity emanate from the chevron apices, and counter-rotating streamwise vortices of axial and radial vorticity develop from the chevron notches. The decay of streamwise vortices is accompanied by the formation of C-shaped structures. The three-dimensional analysis allows quantifying the vortex stretching and tilting activity, which, for the circular jet exit, is related to the azimuthal instabilities and the streamwise vortices connecting the vortex rings. In the chevron jet, stretching and tilting peak during the formation of C-structures. Following Powell’s aeroacoustic analogy, the spatial distribution of the source term is mapped, evaluating the temporal derivative of the Lamb vector. The spatio-temporal evolution of such source term is visualized revealing that the events of highest activity are associated with the processes of vortex-ring pairing and vortex-ring disruption for the circular jet, and with the decay of streamwise instabilities and the formation of C-shaped structures for the chevron case. Subject acoustic noiseaeroacousticsflow instabilityflow visualisationjetsspatiotemporal phenomenaturbulencevortices To reference this document use: http://resolver.tudelft.nl/uuid:36a6086e-ced5-4396-8161-42e50a775a9e DOI https://doi.org/10.1063/1.3665141 Publisher American Institute of Physics ISSN 1070-6631 Source http://link.aip.org/link/doi/10.1063/1.3665141 Source Physics of Fluids, 23 (12), 2011 Part of collection Institutional Repository Document type journal article Rights (c) 2011 The Author(s)American Institute of Physics Files PDF PhysFluids_23_1241041.pdf 11.69 MB Close viewer /islandora/object/uuid:36a6086e-ced5-4396-8161-42e50a775a9e/datastream/OBJ/view