A Numerical Analysis of Vortex Dislocation in Wake-type Flow with Different Spanwise Nonuniformity

Ling, Guocan

doi:10.1142/9789812703439_0009

Cited by 2 publications

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“…This approach minimizes the spurious perturbation waves propagated upstream. For these reasons a form of nonreflecting outlet conditions were used which is an analog of the classical wave equation, suggested by Jin and Braza 19 and generalized to three-dimensional case by our previous studies 16,17 ͑it is noticed that the similar result was also obtained by Persillon and Braza 20 ͒. The nonreflecting boundary conditions at the outlet position of the computation domain are formulated as…”

Section: Boundary Conditionsmentioning

confidence: 82%

“…Darekar and Sherwin 8 studied the flow past a square-section cylinder with a wavy stagnation face. Ling and Zhao 11 and Ling and Niu 12 performed some numerical studies for exploration of vortex dislocation caused by a local disturbance in a wake-type flow. However for qualitative and quantitative understanding of dynamical behavior of vortex in various practical wake flows and many basic problems, which require parametric investigations, such DNS computations could still become prohibitively expensive.…”

Section: Introductionmentioning

confidence: 99%

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Vortex dislocations in wake-type flow induced by spanwise disturbances

Ling

Zhao

2009

Physics of Fluids

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Vortex dislocations in wake-type flow induced by three types of spanwise disturbances superimposed on an upstream velocity profile are investigated by direct numerical simulations. Three distinct modes of vortex dislocations and flow transitions have been found. A local spanwise exponential decay disturbance leads to the appearance of a twisted chainlike mode of vortex dislocation. A stepped spanwise disturbance causes a streamwise periodic spotlike mode of vortex dislocation. A spanwise sinusoidal wavy disturbance with a moderate waviness causes a strong unsteadiness of wake behavior. This unsteadiness starts with a systematic periodic mode of vortex dislocation in the spanwise direction followed by the spanwise vortex shedding suppressed completely with increased time and the near wake becoming a steady shear flow. Characteristics of these modes of vortex dislocation and complex vortex linkages over the dislocation, as well as the corresponding dynamic processes related to the appearance of dislocations, are described by examining the variations of vortex lines and vorticity distribution. The nature of the vortex dislocation is demonstrated by the substantial vorticity modification of the spanwise vortex from the original spanwise direction to streamwise and vertical directions, accompanied by the appearance of noticeable vortex branching and complex vortex linking, all of which are produced at the locations with the biggest phase difference or with a frequency discontinuity between shedding cells. The effect of vortex dislocation on flow transition, either to an unsteady irregular vortex flow or suppression of the Kármán vortex shedding making the wake flow steady state, is analyzed. Distinct similarities are found in the mechanism and main flow phenomena between the present numerical results obtained in wake-type flows and the experimental-numerical results of cylinder wakes reported in previous studies.

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