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UBC Theses and Dissertations

Phase front analysis of laminar vortex streets Lefrançois, Marcel


The continuous formation and development of a laminar vortex street behind a circular cylinder has been modelled as a Huygens-type wave process. The phase of a point next to the cylinder is defined by the amplitude and phase of secondary wavelet centres along the preceding vortexin the near wake. Vortices are located at places where the phase in each cycle is 0 or n. The phase is defined from a Kirchhoff-type phase-amplitude integral which is derived from the Biot-Savart law. Model predictions agree with reported experimental results on cylinders with steps and tapers, and with our own tapered cylinder experiments. To test the predictive power of the model, with regards to preset phase, experiments were performed with new experimental techniques that allow us to set the start-up phase of vortex shedding. The experiments yield known starting conditions, which, when introduced into the phase front model, yield predictions of the street in good agreement with the experiments with regard to the shape and position of the shed vortices in the wake.

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