Automated identification and characterization method of turbulent bursting from single-point records of the velocity field

TL;DR

This paper introduces an automated method for accurately identifying turbulent bursting periods from single-point velocity records, using normalized TKE dissipation rates, applicable across various flow fields without requiring detailed burst-generation mechanisms.

Contribution

The paper presents a novel, automated approach for detecting turbulent bursts from velocity data that does not depend on flow-specific thresholds or detailed burst mechanisms.

Findings

Method accurately identifies burst periods in turbulent flows.

Spectral analysis shows similarity to Kolmogorov theory during non-bursting periods.

Temperature dissipation rates decrease during bursting periods.

Abstract

A new automated method capable of accurately identifying bursting periods in single-point turbulent velocity field records is presented. Manual selection of the method sensitivity (tau*) and threshold (eT) are necessary for effective discrimination between burst periods and the background turbulent flow fluctuations (burst-free periods). The flow characteristic used for identification is the normalized 'instantaneous' TKE dissipation rate levels, calculated using sliding window averaging. Use of the record root mean square and average values for normalization eliminates the need for definition of a physics-based flow-specific threshold. Instead, the suitable sensitivity range and the threshold parameters are selected based on preliminary examination of the velocity records. This, potentially, makes the method applicable for use across various flow fields, especially as it does not require resolving the burst-generation mechanism. The method performance is examined using a field obtained dataset of buoyancy driven turbulent boundary layer flow. Here, the selection of a two-fold (eT=2) increase is used and the sensitivity of the method is examined. Spectral shapes of non-bursting periods show distinguished similarity to those of the Kolmogorov theory, while the bursting period spectral shapes vary significantly. Low resolution records of temperature fluctuations were observed to exhibit a significant decrease in temperature (scalar) dissipation rate during bursting periods. Based on this observation and additional processing, a statistical examination of temperature (scalar) dissipation rate is presented along with a normalization procedure. Future examination of additional scalar variations, i.e. particulate matter and/or gaseous pollutant concentrations, in connection with turbulent bursting periods can assist in further understanding of bursting generation and scalar transfer processes.