Abstract
The wake dynamics behind a long circular cylinder in cross-flow was studied using the POD method. The temporal parts of POD modes, Chronoses, are subjected to frequency analysis. Five groups of modes are distinguished according to the frequency contents. The low order high energy modes contain the vortex shedding frequency or its harmonics up to 3rd order plus Kolmogorov spectrum. The higher order modes are characterized by combination of Kolmogorov spectrum with the white noise spectrum, its importance grows with the mode order. The very high order modes are characterised by the white noise spectrum only.
Highlights
The wake behind a long circular cylinder, virtually infinite, belongs to so called canonical cases in fluid mechanics, those what are well investigated by all means available
The results are to be presented in dimensionless form, coordinates are expressed in multiples of the cylinder diameter d and velocities in multiples of incoming velocity Ui
All other quantities are non-dimensioned with help of the d and Ui as well
Summary
The wake behind a long circular cylinder, virtually infinite, belongs to so called canonical cases in fluid mechanics, those what are well investigated by all means available. The wake dynamical behaviour is presented to be governed by the periodical phenomenon characterized by fundamental frequency. This phenomenon is connected with periodical separation of vortical structures, so called von Kármán-Bénard vortex street. The dimensionless frequency is called Strouhal number St and it is defined as follows: St = (f.d)/U, where f is the fundamental frequency, d is the cylinder diameter and U is the incoming velocity. Typical value of the Strouhal number is about St = 0.2 in the broad range of Reynolds numbers, higher than 200
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