Organized motions in a jet in crossflow

Abstract

An experimental study to identify the structures present in a jet in crossflow has been carried out at a jet-to-crossflow velocity ratio U/Ucf = 3.8 and Reynolds number Re = UcfD/v = 6600. The hot-wire velocity data measured with a rake of eight X-wires at x/D = 5 and 15 and flow visualizations using planar laser-induced fluorescence (PLIF) confirm that the well-established pair of counter-rotating vortices is a feature of the mean field and that the upright, tornado-like or Fric's vortices that are shed to the leeward side of the jet are connected to the jet flow at the core. The counter-rotating vortex pair is strongly modulated by a coherent velocity field that, in fact, is as important as the mean velocity field. Three different structures – folded vortex rings, horseshoe vortices and handle-type structures – contribute to this coherent field. The new handle-like structures identified in the current study link the boundary layer vorticity with the counter-rotating vortex pair through the upright tornado-like vortices. They are responsible for the modulation and meandering of the counter-rotating vortex pair observed both in video recordings of visualizations and in the instantaneous velocity field. These results corroborate that the genesis of the dominant counter-rotating vortex pair strongly depends on the high pressure gradients that develop in the region near the jet exit, both inside and outside the nozzle.

Autoignition of hydrogen/nitrogen jets in vitiated air crossflows at different pressures

“…The broad range where ignition kernels originated and the overlap of regions with flame-stabilizing and non-stabilizing kernels are due to the strong dependence of autoignition on the local strain, temperature, and mixture fraction histories of specific fluid parcels. In the current configuration, these fluid parcels are influenced by random turbulent fluctuations and coherent vortex shedding and motion of the jet [7,25]. In addition, the experimental temperature deviation contributes to the distribution, since the ignition kernel location was found to be strongly dependent on the temperature [10].…”

Vortices and heat flux around a wall-mounted cube cooled simultaneously by a jet and a crossflow

“…A pressure drop develops around the jet in the crossflow direction, which creates a recirculation zone behind it just as in flows around bluff bodies. The intensity of this effect depends on the velocity ratio a v , which governs the interaction of the two streams and their mixing in the jet periphery, Rivero et al [11]. Due to collision of the two mutually perpendicular streams and the shear-driven entrainment, the jet begins to acquire a characteristic kidney shape.…”

Recent Advances in Modeling Axisymmetric Swirl and Applications for Enhanced Heat Transfer and Flow Mixing

“…Consequently, Figure 19C shows that these two jets are unable to reach the lower plate. This is a basic effect of conventional jets in crossflow (Blevins, 1992;Chassaing et al, 1974;Goldstein and Behbahani, 1982;Kamotani and Greber, 1974;Kavsaoglu and Schetz, 1989;Kawai and Lele, 2007;Kiel et al, 2003;Patankar, Basu, and Alpay, 1977;Rivero, Ferre, and Giralt, 2001;Sucec and Bowley, 1976;Nirmolo, 1970;Pratte and Baines, 1967), and swirling jets in crossflow (Denev, Frohlich, and Bockhorn, 2009;Kamal, 2009;Kavsaoglu and Schetz, 1989): the higher the ratio of crossflow velocity to the jet velocity, the faster the jet will bend in a parabolic profile. Figure 19D shows the fluid temperature as seen from the bottom.…”