Author(s): Vaclav Kolar
Linked Author(s):
Keywords: Jet in crossflow; Discharge; Vortex geometry; Vortical structures; Transverse jets
Abstract: The jet-in-crossflow discharge formed as the single circular jet issuing normally into a crossflow, frequently called "transverse jet" or "jet in crossflow" (JICF), represents one of the basic jet-flow configurations with a wide variety of engineering and environmental applications. The JICF phenomenon is closely associated with buoyant jets and plumes where density distribution (due to initial jet-to-crossflow difference and/or crossflow stratification) plays a crucial role. Though the JICF is characterized in the near field by a relatively complex vortical structure consisting of both steady and unsteady coherent vortical structures, it is well known that the dominant vortical mean-flow feature is a secondary-flow contrarotating vortex pair (CVP). The CVP occurs as a result of the impulse of the jet on the crossflow, forming itself in the near field and becoming dominant in the far field. While many papers have studied various fluid-dynamical aspects of the JICF in detail, the description of the CVP structure in terms of vorticity fields is relatively scarce in open literature. Moreover, though vorticity appears as the primary quantity for the description of vortical structures, it has been recently well recognized that vorticity does not provide a true vortex geometry because of not distinguishing the effect of a "background shearing" from the "actual swirling motion of a vortex". In the present work, a novel approach to vortex core identification based on the triple decomposition of the local relative motion near a point is applied to the above mentioned CVP. The present paper demonstrates that a specific portion of vorticity provides a proper physical quantity for the detection of vortex cores. In this regard, vorticity is decomposed into two parts, shear vorticity and residual vorticity. The residual vorticity is associated with the local residual rigid-body rotation near a point obtained after the extraction of an effective pure shearing motion. The main result regarding the JICF vortex geometry clearly indicates that while the CVP vorticity distribution is characterized by the well-known prolonged contours, the vortex-core geometry described by the residual vorticity (after extracting an effective pure shearing motion) is nearly circular.
Year: 2005