Amplitude and frequency modulation in a turbulent jet at high Reynolds number

Abstract (2014)

Authors

D. Fiscaletti Fluid Mechanics - Mechanical, Maritime and Materials Engineering
B Ganapathisubramani University of Southhampton
G.E. Elsinga Fluid Mechanics - Mechanical, Maritime and Materials Engineering
Research Group
Fluid Mechanics (Mechanical, Maritime and Materials Engineering) (TU Delft)
More Info
expand_more

Published Date

2014

Language

English

Reuse Rights

Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.

Faculty

Mechanical, Maritime and Materials Engineering

Department

Process and Energy

Research Group

Fluid Mechanics

Abstract

In this work, the amplitude and frequency modulation of the small scales of turbulence is investigated experimentally in a jet at high Reynolds number. Hot-wire anemometry (HWA) and long-range μPIV measurements are performed in the fully developed region of the jet. From HWA, time series are converted into space series by applying the Taylor hypothesis. Using spectral filters, two signals representative of the large, and the small scales are constructed. It was found that for positive large-scale fluctuations, the associated small-scale signal is stronger in amplitude (amplitude modulation), and presents locally a higher number of local maxima and minima (frequency modulation). Moreover, the local standard deviation of the small-scale signal (representative of the amplitude of the small-scale signal) increases with the local strength of the large-scale fluctuations. A further investigation with PIV allowed to resolve the small scales of turbulence, without the need for Taylor hypothesis. From this analysis, the amount of amplitude modulation was found to be only 25 % of the value obtained with HWA. This difference can be explained considering that the structures of intense vorticity travel, on average, at velocities higher than the mean velocity of the flow.