Influence of finite amplitude perturbations on the vortex shedding past a circular cylinder
Abstract
The influence of finite amplitude perturbations on vortex shedding past a circular cylinder at Re = 1000 is studied by means of a mathematical model. The numerical scheme is a mixed spectral-finite analytic numerical technique which takes advantage of the Fast Fourier Transform (FFT) algorithm to evaluate the nonlinear terms in the two-dimensional time dependent Navier-Stokes equations. The CDC-CYBER 205 supercomputer of the Purdue University Computing Center has been used for the calculations. Each perturbation consists in a pure rotational field which is imposed, at the nondimensional time T = 0, on an initially irrotational flow field. Mathematical formulation of the perturbation vortex is characterized by two quantities, strength S and spread $\sigma$, both depending on the values of two parameters C and n. Six different perturbations are examined, some with increasing strength and constant spread, others with constant strength and increasing spread, each formulation corresponding to a different couple of values of C and n. The effect of each perturbation is evaluated and compared with all others. The results are presented mainly in graphical form; the flow fields are described by means of absolute streamlines, relative streamlines and vorticity fields. A discussion is also presented about the meaning of the different representations of the flow fields. It appears that most effective way of representing the calculated fields and understanding the mechanism of the formation and the shedding of the vortices, is the one of inspecting the part of the streamfunction directly related to the viscosity. This is not the one that one should observe in reality. A new hypothesis is advanced about the vortex shedding mechanism.
Degree
Ph.D.
Advisors
Giorgini, Purdue University.
Subject Area
Civil engineering
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