Construction of differential equations from experimental data of Karman vortex streets
Abstract
The construction of a differential equation from the experimental data of a Karman vortex street shows that the dynamics of the vortex street for Re less than or = 150, measured with a hot wire probe at a distance a less than d from the cylinder axis can be described by a differential equation system. The differential equation of the van der Pol oscillator form is a special case. Both systems can be described by a second order differential equation and third order polynomial. Thus the model of the van der Pol oscillator can be confirmed within the limits mentioned. For the Karman vortex street, though, all the terms are necessary whereas the van der Pol oscillator in this simple form consists of only three terms. The method of construction of a differential equation has several advantages compared to the Fourier transformation. The basic idea of transformations of a measured time series is to find a precise description of the data with a few parameters. If a time series is periodic a Fourier transformation is very useful, since the basic frequency together with its Fourier amplitude and the Fourier amplitudes for higher harmonics provides a description of the data with a few quantities.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 June 1988
 Bibcode:
 1988STIN...8927127R
 Keywords:

 Flow Measurement;
 Karman Vortex Street;
 Vorticity Equations;
 Flow Visualization;
 Polynomials;
 Von Karman Equation;
 Fluid Mechanics and Heat Transfer