ISSN:
1089-7666
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Vortex simulation is used to study a confined two-dimensional, two-stream, spatially developing shear layer, focusing on the effect of upstream forcing on the development of the vorticity field and the entrainment of irrotational fluid into the mixing zone. In the unforced case, the layer rolls up at the most amplified mode as determined from the linear theory, forming eddies that equilibrate to the neutrally stable mode by increasing the local thickness. Subharmonic perturbation returns the state to the most amplified frequency and pairing starts, repeating the sequence of events and leading to the observed self-similarity. In the forced case, eddy interactions follow several stages. First, the layer rolls up at the harmonic of the forcing frequency closest to the most amplified mode. A process of accelerated pairing follows yielding eddies in tune with the forcing frequency. Pairing among resonant eddies, which represent the neutrally stable mode, is disabled and the growth of the vorticity layer is impaired. Finally, the effect of forcing diminishes and pseudorandom pairing is resumed. Velocity fluctuations are strongly affected by forcing, and the sign of Reynolds stresses is reversed following pairing. Entrainment of passive particles is commensurate with the development of the vorticity layer.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.866321
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