Measurement of the gradient field of a turbulent free surface
Measurement of the gradient field of a turbulent free surface
We study the free surface above a turbulent channel flow. We describe a laser scanning technique that can be used to measure the space–time turbulent surface gradient field along a line. A harmonically swiveling laser beam is focused on the surface and its angle of refraction is measured using a position sensing device. The registered signals can be converted easily to the desired gradient field, and spectra and correlations can be measured. Examples of measured spectra and correlation functions of the surface above a turbulent channel flow (Reynolds number R ? ? 250) demonstrate the viability of the technique. We further assess the validity of Taylor’s frozen turbulence hypothesis that implies that time-dependent signals measured along a line that is oriented perpendicularly to the mean channel velocity can be interpreted as 2D measurements of the surface slope. While Taylor’s hypothesis works for a turbulent velocity field, it does not work for its free surface.
waves velocity spectra
629-640
Savelsberg, Ralph
89477d47-a40d-486f-b8d7-ef6a695ed983
Holten, A.P.C
ca23d17f-84bc-4269-8432-056883de4d5b
van de Water, W.
6adc6d77-0764-4e7c-b8f8-8fbafafa9d05
October 2006
Savelsberg, Ralph
89477d47-a40d-486f-b8d7-ef6a695ed983
Holten, A.P.C
ca23d17f-84bc-4269-8432-056883de4d5b
van de Water, W.
6adc6d77-0764-4e7c-b8f8-8fbafafa9d05
Savelsberg, Ralph, Holten, A.P.C and van de Water, W.
(2006)
Measurement of the gradient field of a turbulent free surface.
Experiments in Fluids, 41 (4), .
(doi:10.1007/s00348-006-0186-x).
Abstract
We study the free surface above a turbulent channel flow. We describe a laser scanning technique that can be used to measure the space–time turbulent surface gradient field along a line. A harmonically swiveling laser beam is focused on the surface and its angle of refraction is measured using a position sensing device. The registered signals can be converted easily to the desired gradient field, and spectra and correlations can be measured. Examples of measured spectra and correlation functions of the surface above a turbulent channel flow (Reynolds number R ? ? 250) demonstrate the viability of the technique. We further assess the validity of Taylor’s frozen turbulence hypothesis that implies that time-dependent signals measured along a line that is oriented perpendicularly to the mean channel velocity can be interpreted as 2D measurements of the surface slope. While Taylor’s hypothesis works for a turbulent velocity field, it does not work for its free surface.
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Published date: October 2006
Keywords:
waves velocity spectra
Organisations:
Aerodynamics & Flight Mechanics
Identifiers
Local EPrints ID: 43262
URI: http://eprints.soton.ac.uk/id/eprint/43262
ISSN: 0723-4864
PURE UUID: c085e4de-e35a-46eb-b843-b8c4d8727aa8
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Date deposited: 22 Jan 2007
Last modified: 15 Mar 2024 08:54
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Contributors
Author:
Ralph Savelsberg
Author:
A.P.C Holten
Author:
W. van de Water
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