Vortex ring evolution in an impulsively started jet using digital particle image velocimetry and continuous wavelet analysis

Abstract

Digital particle image velocimetry and wavelet analysis are combined in this work in order to study the characteristics of the leading vortex ring generated in an impulsively starting jet flow. The wavelet analysis allows one, by virtue of its properties of selectivity in space and scale, to detect coherent structures and to compute their position and size and, through further processing, their convection velocity and circulation. It has been observed that the energy of the leading vortex ring continuously increases even after it has pinched off from the jet shear layer generating it.

Propulsive force calculations in swimming frogs II. Application of a vortex ring model to DPIV data

“…Most papers in the quite large body of literature on vortex ring phenomena examine the creation and evolution of vortex rings originating from pipes or nozzles (e.g. Schramm and Riethmuller, 2001;Shusser and Gharib, 2000). The creation of vortex rings by (flat) surfaces moving through free fluid, comparable to the frog kick, and the energetics during the vortex creation process, have had little attention so far.…”

Shannon Entropy-Based Wavelet Transform Method for Autonomous Coherent Structure Identification in Fluid Flow Field Data

“…We chose the Ricker wavelet (as represented by Equation (1)) for this reason. The two-dimensional Ricker wavelet is considered as smooth in the physical space and resembles the shape of vorticity associated with a vortex [42,44,45]. In addition, it bears resemblance to an Oseen vortex, as reported in an earlier study conducted by Schram and Riethmuller [42].…”

“…The two-dimensional Ricker wavelet is considered as smooth in the physical space and resembles the shape of vorticity associated with a vortex [42,44,45]. In addition, it bears resemblance to an Oseen vortex, as reported in an earlier study conducted by Schram and Riethmuller [42]. Varun et al [45] pointed out that the Ricker wavelet is a promising kernel that resembles most of the test properties for the Hamel-Oseen solution presented by Schram et al [46].…”

“…The application of wavelet decomposition methods to experimental data was demonstrated by Schram and Riethmuller [42], who applied it to digital particle image velocimetry (PIV) data for the vortical structure detection of the leading vortex ring generated in an impulsively starting jet flow. Camussi [3] proposed a method based on the analysis of the local energy content at separated scales, to extract the typical wavenumber associated with structures and, therefore, the typical length-scale of coherent structures.…”

“…In particular, our implementation involves the use of continuous wavelet transform (CWT), which can be associated with wide, unbounded range of scales and unrestricted characteristics of dilation, translation or rotation [2,3,42,44]. It is important to note that Farge et al [12] were among the first to demonstrate two-dimensional CWT on data from numerical simulations pertaining to near-wall dynamics of three-dimensional turbulent channel flow using a complex-valued function (Morlet wavelet).…”