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Kruse N. — Isothermal and Non-Isothermal Turbulent Flow over Solid Waves Transport and Structure
Kruse N. — Isothermal and Non-Isothermal Turbulent Flow over Solid Waves Transport and Structure

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Название: Isothermal and Non-Isothermal Turbulent Flow over Solid Waves Transport and Structure

Автор: Kruse N.

Аннотация:

An experimental study on transport phenomena in a turbulent flow with
separation in a wide water channel (aspect ratio 12:1) is presented. The
wavy bottom wall, characterized by the wavelength  and the wave amplitude
2a, is heated with a constant heat flux under non-isothermal
condition. Spatiotemporal information on the flow velocity is obtained
from digital particle image velocimetry (PIV). Digital particle image
thermometry (PIT) is used to assess simultaneously the temporal and
spatial variation of velocity and temperature fields. The temperature
is measured with thermochromic liquid crystal particles (TLC) which
change their reflected wavelengths as a function of the temperature.
At isothermal conditions, measurements are performed at Reynolds numbers
up to 20500, defined with the bulk velocity and the half-height of the
channel. Large ensembles of instantaneous velocity fields are decomposed
into orthogonal eigenfunctions. A projection of instantaneous snapshots
of the velocity field onto eigenfunctions is used to extract the time development
of flow structures of defined kinetic energy. Large longitudinal
structures with a characteristic spanwise scale O{1.5Λ} can be found
by projecting instantaneous realizations of the flow onto the first two
eigenfunctions. Any interactions between coherent structures result in a
merger into newer structures via complete, partial, and fractional pairings
or divisions. The structures retain the characteristic separation and
contribute significantly to the kinetic energy. The meandering motion of
O{1.5Λ}-scales provides a mechanism for the transport of momentum.
To quantify how turbulence statistics and eigenfunctions in the outer part of the shear layer depend on the interaction with the wall, three
wavy surfaces, characterized by different amplitude-to-wavelength ratios,
are investigated. Similar dominant eigenfunctions with similar spanwise
scales are obtained in the outer part of the wall shear layer. The
root-mean-square of the streamwise and spanwise velocity fluctuations,
Reynolds shear stress, Reynolds stress coefficients, and turbulent kinetic
energy are approximately the same regardless the surface roughness,
when normalized with the friction velocity. The structure of stress producing
motions in the outer flow could have a universal character, in
that they are influenced by turbulence producing processes in the inner
flow only through the magnitude of the friction velocity.


Язык: en

Рубрика: Физика/

Тип: Диссертация

Статус предметного указателя: Неизвестно

ed2k: ed2k stats

Год издания: 2005

Количество страниц: 225

Добавлена в каталог: 26.06.2006

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