A Multiresolution Census Algorithm for Calculating Vortex Statistics in Turbulent Flows

TL;DR

This paper introduces a multiresolution algorithm using wavelet transforms and regression to accurately identify and analyze vortex structures in turbulent flow simulations, capturing their size, shape, and physical properties.

Contribution

The paper presents a novel multiresolution vortex census algorithm that employs wavelet transforms and regression to detect and characterize vortices in turbulent flows.

Findings

Accurately extracts vortices of various shapes and sizes.

Reproduces known physical scaling laws in vortex evolution.

Provides detailed vortex statistics over time.

Abstract

The fundamental equations that model turbulent flow do not provide much insight into the size and shape of observed turbulent structures. We investigate the efficient and accurate representation of structures in two-dimensional turbulence by applying statistical models directly to the simulated vorticity field. Rather than extract the coherent portion of the image from the background variation, as in the classical signal-plus-noise model, we present a model for individual vortices using the non-decimated discrete wavelet transform. A template image, supplied by the user, provides the features to be extracted from the vorticity field. By transforming the vortex template into the wavelet domain, specific characteristics present in the template, such as size and symmetry, are broken down into components associated with spatial frequencies. Multivariate multiple linear regression is used to fit the vortex template to the vorticity field in the wavelet domain. Since all levels of the template decomposition may be used to model each level in the field decomposition, the resulting model need not be identical to the template. Application to a vortex census algorithm that records quantities of interest (such as size, peak amplitude, circulation, etc.) as the vorticity field evolves is given. The multiresolution census algorithm extracts coherent structures of all shapes and sizes in simulated vorticity fields and is able to reproduce known physical scaling laws when processing a set of voriticity fields that evolve over time.