Three-dimensional Vortex Modeling of Unforced Transverse Jets (original) (raw)
Related papers
On the formation of the counter-rotating vortex pair in transverse jets
2001
Among the important physical phenomena associated with the jet in crossflow is the formation and evolution of vortical structures in the flow field, in particular the counter-rotating vortex pair (CVP) associated with the jet cross-section. The present computational study focuses on the mechanisms for the dynamical generation and evolution of these vortical structures. Transient numerical simulations of the flow field are performed using three-dimensional vortex elements. Vortex ring rollup, interactions, tilting, and folding are observed in the near field, consistent with the ideas described in the experimental work of , for example. The time-averaged effect of these jet shear layer vortices, even over a single period of their evolution, is seen to result in initiation of the CVP. Further insight into the topology of the flow field, the formation of wake vortices, the entrainment of crossflow, and the effect of upstream boundary layer thickness is also provided in this study.
On the vorticity dynamics of a turbulent jet in a crossflow
Journal of Fluid Mechanics, 1986
We present numerical solutions of the fully three-dimensional flow of a round, turbulent jet emitted normal to a uniform free stream. Comparisons with available laboratory data and comparison between different numerical grid resolutions are used to demonstrate the quality of the simulation. Examination of the detailed flow pattern within a computational domain, which extends 15 jet diameters from the source allows us to follow the vorticity dynamics in the transition from an initially vertical jet to a wake with a vortex pair essentially aligned with the free stream. The transition is presented as a function of the ratio of the jet exit velocity to free stream velocity. For large velocity ratios, the source of the streamwise vorticity in the vortex pair can be readily traced back to the original streamwise vorticity in the sides of the vertical jet.
Effects of controlled vortex generation and interactions in transverse jets
Physical Review Fluids
This experimental study examined the effects of controlled vortex generation and interactions created by axisymmetric excitation of a transverse jet, with a focus on the structural and mixing characteristics of the flow. The excitation consisted of a double-pulse forcing waveform applied to the jet, where two distinct temporal square-wave pulses were prescribed during a single forcing period. The two distinct pulses produced vortex rings of different strength and celerity, the strategic selection of which promoted vortex ring interactions or collisions in the near field to varying degrees. Jet flow conditions corresponding to a transitionally convectively and absolutely unstable upstream shear layer (USL) in the absence of forcing, at a jet-to-cross-flow momentum flux ratio of J = 10, and to an absolutely unstable USL at J = 7, were explored for a jet Reynolds number of 1800. Acetone planar laser-induced fluorescence imaging was utilized to quantify the influence of different prescribed temporal waveforms. All forcing conditions enhanced the spread, penetration, and molecular mixing of the jet as compared to the unforced jet, though to differing degrees. Interestingly, when the jet was convectively unstable, forcing which promoted vortex collisions provided the greatest enhancement in molecular mixing, whereas the absolutely unstable jet produced the greatest enhancement in mixing when the vortex rings did not interact, with important implications for optimized jet control.
Direct numerical simulations of round jets: Vortex induction and side jets
Physics of Fluids, 1994
In this paper, a numerical investigation of three-dimensional round jets subjected to streamwise and azimuthal perturbations is reported. The main objective of the study is to give a consistent scenario for the breaking of rotational symmetry in such flows which may ultimately lead to the production of intense side jets. In particular it is shown that the development of the Widnall instability on the primary vortex rings and the evolution of the Bernal and Roshko [J. Fluid Mech. 170, 499 (1986)] streamwise vortices generated by the instability of the braid could be deeply intertwined. A comprehensive discussion of the vortex induction mechanisms leading to the reorientation of the initial vorticity both in the ring and braid regions and to the deformation of the rings is presented. The recent analysis by Monkewitz and Pfizenmaier [Phys. Fluids A 3, 1356 (1991)] is confirmed in the sense that strong radial ejection of fluid is not directly linked to the deformation of the vortex ring...
Simulations of High Speed Turbulent Jets in Crossflow
2010
Numerical simulations are used to study an under-expanded sonic jet injected into a supersonic crossflow and an over-expanded supersonic jet injected into a subsonic crossflow, where the flow conditions are based on Santiago et al.'s (1997) and Beresh et al.'s (2005) experiments, respectively. A finite volume compressible Navier--Stokes solver developed by Park & Mahesh (2007) for unstructured grids is used. The simulations successfully reproduce experimentally observed shock systems and flow vortical structures such as the barrel shock, Mach disk, horseshoe vortices that wrap up in front of the jet and the counter rotating vortex pair (CVP) downstream of the jet. The dynamics of these flow structures are discussed, as well as the influence of grid resolution and the effect of inflow turbulence. The time averaged flow fields are compared to the experimental results, and reasonable agreement is observed.
Direct numerical simulations of transient turbulent jets: vortex-interface interactions
Journal of Fluid Mechanics, 2021
The breakup of an interface into a cascade of droplets and their subsequent coalescence is a generic problem of central importance to a large number of industrial settings such as mixing, separations, and combustion. We study the breakup of a liquid jet introduced through a cylindrical nozzle into a stagnant viscous phase via a hybrid interface-tracking/level-set method to account for the surface tension forces in a threedimensional Cartesian domain. Numerical solutions are obtained for a range of Reynolds (Re) and Weber (We) numbers. We find that the interplay between the azimuthal and streamwise vorticity components leads to different interfacial features and flow regimes in Re-We space. We show that the streamwise vorticity plays a critical role in the development of the three-dimensional instabilities on the jet surface. In the inertiacontrolled regime at high Re and We, we expose the details of the spatio-temporal development of the vortical structures affecting the interfacial dynamics. A mushroomlike structure is formed at the leading edge of the jet inducing the generation of a liquid sheet in its interior that undergoes rupture to form droplets. These droplets rotate inside the mushroom structure due to their interaction with the prevailing vortical structures. Additionally, Kelvin-Helmholtz vortices that form near the injection point deform in the streamwise direction to form hairpin vortices, which, in turn, trigger the formation of interfacial lobes in the jet core. The thinning of the lobes induces the creation of holes which expand to form liquid threads that undergo capillary breakup to form droplets.
Experiments in Fluids, 2013
Circular flush Jets In Cross-Flow were experimentally studied in a water tunnel using Volumetric Particle Tracking Velocimetry, for a range of jet to cross-flow velocity ratios, r, from 0.5 to 3, jet exit diameters d from 0.8 cm to 1 cm and cross-flow boundary layer thickness δ from 1 to 2.5 cm. The analysis of the 3D mean velocity fields allows for the definition, computation and study of Counter-rotating Vortex Pair trajectories. The influences of r, d and δ were investigated. A new scaling based on momentum ratio r m taking into account jet and cross-flow momentum distributions is introduced based on the analysis of jet trajectories published in the literature. Using a rigorous scaling quality factor Q to quantify how well a given scaling successfully collapses trajectories, we show that the proposed scaling also improves the collapse of CVP trajectories, leading to a final scaling law for these trajectories.
The Vortex Dominated Flow Field Associated with a Confined Jet in a Crossflow
2006
This study focuses on the near field mixing of a confined circular jet that is being injected normally from a wall into a subsonic crossflow in a confined area. The streamwise, transverse and lateral mean velocities were obtained using a two-component Laser Doppler Anemometer. From these quantities the time average vorticity in three dimensions were estimated for locations between 1.5 and 4.5 jet diameters downstream of the jet exit. The jet to crossflow velocity ratio was kept constant at four. The results highlight a complex system of vortices within this flowfield that is different to that of a free jet in a crossflow. In addition the present study was able to quantify changes in the vortical structures as a function of downstream distance as well as provides evidence of what effect freestream turbulence has on the evolving vorticity.