Showing papers by "Fernando F. Grinstein published in 1995"

Near field dynamics of subsonic free square jets. A computational and experimental study

Abstract: Results of a combined numerical and experimental investigation of the near field of low‐subsonic air square jets are presented The study focuses on examining the role of initial conditions and other features of the jet dynamics in determining the nature and frequency of occurrence of axis switching and the related mechanisms which enhance entrainment, mixing, and turbulence production Three different experimental square jet facilities were utilized, including orifice jets with low and high initial turbulence level, and pipe jets Unsteady, spatially developing jets were investigated computationally using direct and monotonically‐integrated large‐eddy simulation approaches, and appropriate inflow/outflow boundary conditions Insight on the axis‐switching process was obtained using the detailed database from the simulations to investigate how the unsteady vorticity dynamics reflects on the time‐averaged properties of the jet cross sections The different experimental jets were chosen such that important p

Self-induced vortex ring dynamics in subsonic rectangular jets

Abstract: The development in space and time of vortex rings in low aspect‐ratio (AR) rectangular jets is investigated. By design, the present studies isolate the self‐induced ring dynamics from effects of unsteady events otherwise present upstream and downstream of the rings in developed jets. The simulations show that the vortex rings undergo quite regular self‐induced nonplanar deformations, approximately recovering their shape and flatness with axis rotated with respect to their initial configuration. The axis‐rotation periods are in good agreement with previously reported data for pseudoelliptic rings, and exhibit nearly linear growth rate as a function of AR. For the larger aspect‐ratio case studied (AR=4), bifurcation of the ring due to vortex reconnection into roughly round rings is observed, followed by collision of the split rings and a new reconnection process, suggesting pathways for transition to turbulence based on self‐induced vortex deformations and reconnections.

Vorticity in Jets

Abstract: Among nature’s omnipresent phenomena are fluid dynamic jets Some are obvious to even the most casual observer — like the jets that exit from one’s mouth and nostrils when exhaling on a cold morning Others require extraordinary efforts to see — like astrophysical jets, which at distances of light years away are visible only through the telescopes of the astronomer The jets of technology dominate our lives, from propelling the planes that move us across continents, to issuing from the simple air hoses of the machine shop, from the stacks that spew the waste products of industry, to the diffuser arrays that disperse effluent into our streams and rivers Without jets, life as we know it would be unimaginable