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Characteristics of sources and sinks of momentum in a turbulent boundary layer

Characteristics of sources and sinks of momentum in a turbulent boundary layer
Characteristics of sources and sinks of momentum in a turbulent boundary layer
In turbulent boundary layers, the wall-normal gradient of the Reynolds shear stress identifies momentum sources and sinks (T=∂[−uv]/∂y). These motions can be physically interpreted in two ways {i.)} as contributors to the turbulence term balancing the mean momentum equation, and {ii.)} as regions of strong local interaction between velocity and vorticity fluctuations. In this paper, the space-time evolution of momentum sources and sinks are investigated in a turbulent boundary layer at the Reynolds number (Reτ) = 2700, with time-resolved planar particle image velocimetry in a plane along the streamwise and wall-normal directions. Wavenumber--frequency power spectra of T fluctuations reveal that the wave velocities of momentum sources and sinks tend to match the local streamwise velocity in proximity to the wall. However, as the distance from the wall increases, the wave velocities of the T events are slightly lower than the local streamwise velocities of the flow, which is also confirmed from the tracking in time of the intense momentum sources and sinks. This evidences that momentum sources and sinks are preferentially located in low-momentum regions of the flow. The spectral content of the T fluctuations is maximum at the wall, but it decreases monotonically as the distance from the wall grows. The relative spectral contributions of the different wavelengths remains unaltered at varying wall-normal locations. From autocorrelation coefficient maps, the characteristic streamwise and wall-normal extents of the T motions are respectively 60 and 40 wall-units, independent of the wall distance. Both statistics and instantaneous visualizations show that momentum sources and sinks have a preferential tendency to be organized in positive-negative pairs in the wall-normal direction.
2469-990X
Fiscaletti, Daniele
b60d3ad4-c0c7-4990-b141-ecec8f90b4c9
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Fiscaletti, Daniele
b60d3ad4-c0c7-4990-b141-ecec8f90b4c9
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052

Fiscaletti, Daniele and Ganapathisubramani, Bharathram (2018) Characteristics of sources and sinks of momentum in a turbulent boundary layer. Physical Review Fluids, [054601]. (doi:10.1103/PhysRevFluids.3.054601).

Record type: Article

Abstract

In turbulent boundary layers, the wall-normal gradient of the Reynolds shear stress identifies momentum sources and sinks (T=∂[−uv]/∂y). These motions can be physically interpreted in two ways {i.)} as contributors to the turbulence term balancing the mean momentum equation, and {ii.)} as regions of strong local interaction between velocity and vorticity fluctuations. In this paper, the space-time evolution of momentum sources and sinks are investigated in a turbulent boundary layer at the Reynolds number (Reτ) = 2700, with time-resolved planar particle image velocimetry in a plane along the streamwise and wall-normal directions. Wavenumber--frequency power spectra of T fluctuations reveal that the wave velocities of momentum sources and sinks tend to match the local streamwise velocity in proximity to the wall. However, as the distance from the wall increases, the wave velocities of the T events are slightly lower than the local streamwise velocities of the flow, which is also confirmed from the tracking in time of the intense momentum sources and sinks. This evidences that momentum sources and sinks are preferentially located in low-momentum regions of the flow. The spectral content of the T fluctuations is maximum at the wall, but it decreases monotonically as the distance from the wall grows. The relative spectral contributions of the different wavelengths remains unaltered at varying wall-normal locations. From autocorrelation coefficient maps, the characteristic streamwise and wall-normal extents of the T motions are respectively 60 and 40 wall-units, independent of the wall distance. Both statistics and instantaneous visualizations show that momentum sources and sinks have a preferential tendency to be organized in positive-negative pairs in the wall-normal direction.

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Characteristics of sources and sinks of momentum in a turbulent - Accepted Manuscript
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Accepted/In Press date: 13 April 2018
e-pub ahead of print date: 3 May 2018

Identifiers

Local EPrints ID: 420210
URI: http://eprints.soton.ac.uk/id/eprint/420210
ISSN: 2469-990X
PURE UUID: b6d284e1-9ad4-45c0-8c8a-eeb256c679e6
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

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Date deposited: 02 May 2018 16:30
Last modified: 22 Nov 2021 06:21

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Author: Daniele Fiscaletti

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