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Coherent structures in the linearized impulse response of turbulent channel flow

Coherent structures in the linearized impulse response of turbulent channel flow
Coherent structures in the linearized impulse response of turbulent channel flow

We study the evolution of velocity fluctuations due to an isolated spatio-temporal impulse using the linearized Navier–Stokes equations. The impulse is introduced as an external body force in incompressible channel flow at Reτ=10000 . Velocity fluctuations are defined about the turbulent mean velocity profile. A turbulent eddy viscosity is added to the equations to fix the mean velocity as an exact solution, which also serves to model the dissipative effects of the background turbulence on large-scale fluctuations. An impulsive body force produces flow fields that evolve into coherent structures containing long streamwise velocity streaks that are flanked by quasi-streamwise vortices; some of these impulses produce hairpin vortices. As these vortex–streak structures evolve, they grow in size to be nominally self-similar geometrically with an aspect ratio (streamwise to wall-normal) of approximately 10, while their kinetic energy density decays monotonically. The topology of the vortex–streak structures is not sensitive to the location of the impulse, but is dependent on the direction of the impulsive body force. All of these vortex–streak structures are attached to the wall, and their Reynolds stresses collapse when scaled by distance from the wall, consistent with Townsend’s attached-eddy hypothesis.
turbulence modelling, turbulent boundary layers
0022-1120
1190-1203
Vadarevu, Sabarish B.
2ef2cfd4-0a70-4bfd-8eab-c5f36eb4183e
Symon, Sean
2e1580c3-ba27-46e8-9736-531099f3d850
Illingworth, Simon J.
0e1c7b04-2c41-4152-996f-6aa92583bf5b
Marusic, Ivan
e8863dbc-d29e-4087-9269-ea1ef1d63f48
Vadarevu, Sabarish B.
2ef2cfd4-0a70-4bfd-8eab-c5f36eb4183e
Symon, Sean
2e1580c3-ba27-46e8-9736-531099f3d850
Illingworth, Simon J.
0e1c7b04-2c41-4152-996f-6aa92583bf5b
Marusic, Ivan
e8863dbc-d29e-4087-9269-ea1ef1d63f48

Vadarevu, Sabarish B., Symon, Sean, Illingworth, Simon J. and Marusic, Ivan (2019) Coherent structures in the linearized impulse response of turbulent channel flow. Journal of Fluid Mechanics, 863, 1190-1203. (doi:10.1017/jfm.2019.15).

Record type: Article

Abstract


We study the evolution of velocity fluctuations due to an isolated spatio-temporal impulse using the linearized Navier–Stokes equations. The impulse is introduced as an external body force in incompressible channel flow at Reτ=10000 . Velocity fluctuations are defined about the turbulent mean velocity profile. A turbulent eddy viscosity is added to the equations to fix the mean velocity as an exact solution, which also serves to model the dissipative effects of the background turbulence on large-scale fluctuations. An impulsive body force produces flow fields that evolve into coherent structures containing long streamwise velocity streaks that are flanked by quasi-streamwise vortices; some of these impulses produce hairpin vortices. As these vortex–streak structures evolve, they grow in size to be nominally self-similar geometrically with an aspect ratio (streamwise to wall-normal) of approximately 10, while their kinetic energy density decays monotonically. The topology of the vortex–streak structures is not sensitive to the location of the impulse, but is dependent on the direction of the impulsive body force. All of these vortex–streak structures are attached to the wall, and their Reynolds stresses collapse when scaled by distance from the wall, consistent with Townsend’s attached-eddy hypothesis.

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More information

e-pub ahead of print date: 30 January 2019
Published date: 25 March 2019
Keywords: turbulence modelling, turbulent boundary layers

Identifiers

Local EPrints ID: 444780
URI: http://eprints.soton.ac.uk/id/eprint/444780
ISSN: 0022-1120
PURE UUID: 2c44758d-0eec-43e9-a4d4-7c9e4b1da966

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Date deposited: 04 Nov 2020 17:31
Last modified: 14 Sep 2021 18:47

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