Energy transfer and dissipation in equilibrium and nonequilibrium turbulence
Author(s)
da Silva Cardoso Isidro Valente, Pedro Manuel
Type
Thesis
Abstract
The nonequilibrium dissipation behaviour discovered for decaying fractal square grid-generated
turbulence is experimentally investigated using hot-wire anemometry in a wind
tunnel. The previous results are consolidated and benchmarked with turbulence generated
by regular square-mesh grids, designed to retain certain geometrical parameters of
the fractal square grid. This comparison shows that the nonequilibrium behaviour is
manifested in both fractal square grid- and regular square-mesh grid-generated turbulence
for a downstream region during the turbulence decay up to the first few multiples
of the wake interaction distance. For one of the regular grids it is shown that beyond this
region there is a transition to the classical dissipation behaviour if the local turbulent
Reynolds number is sufficiently high. A sharp conclusion can thus be drawn that this
behaviour is more general than initially thought and therefore of much greater scientific
and engineering significance.
The nonequilibrium dissipation phenomena is further investigated by experimentally
measuring the terms of an inhomogeneous von Karman-Howarth-Monin equation. This
equation is essentially a scale-by-scale energy transfer budget. From the data it is shown
that the inhomogeneity of the turbulent flow does not tamper with the nonequilibrium
phenomena and that the scaling of the nonlinear energy transfer, i.e. the transfer of
energy to the small-scales, is out of balance with the dissipation. This imbalance leads
to the growth of the small-scale advection to compensate for the increasing gap between
the energy transferred and the energy dissipated.
For the highest Reynolds number data it is also shown that the nonequilibrium dissipation
scaling appears to be consistent with the expectation that it is asymptotically
independent of the viscosity (as the Reynolds number increases) and that the spectra
exhibit a power-law range with the Kolmogorov-Obukhov exponent −5/3. These two
observations are shown to be consistent.
turbulence is experimentally investigated using hot-wire anemometry in a wind
tunnel. The previous results are consolidated and benchmarked with turbulence generated
by regular square-mesh grids, designed to retain certain geometrical parameters of
the fractal square grid. This comparison shows that the nonequilibrium behaviour is
manifested in both fractal square grid- and regular square-mesh grid-generated turbulence
for a downstream region during the turbulence decay up to the first few multiples
of the wake interaction distance. For one of the regular grids it is shown that beyond this
region there is a transition to the classical dissipation behaviour if the local turbulent
Reynolds number is sufficiently high. A sharp conclusion can thus be drawn that this
behaviour is more general than initially thought and therefore of much greater scientific
and engineering significance.
The nonequilibrium dissipation phenomena is further investigated by experimentally
measuring the terms of an inhomogeneous von Karman-Howarth-Monin equation. This
equation is essentially a scale-by-scale energy transfer budget. From the data it is shown
that the inhomogeneity of the turbulent flow does not tamper with the nonequilibrium
phenomena and that the scaling of the nonlinear energy transfer, i.e. the transfer of
energy to the small-scales, is out of balance with the dissipation. This imbalance leads
to the growth of the small-scale advection to compensate for the increasing gap between
the energy transferred and the energy dissipated.
For the highest Reynolds number data it is also shown that the nonequilibrium dissipation
scaling appears to be consistent with the expectation that it is asymptotically
independent of the viscosity (as the Reynolds number increases) and that the spectra
exhibit a power-law range with the Kolmogorov-Obukhov exponent −5/3. These two
observations are shown to be consistent.
Date Issued
2013-02
Date Awarded
2013-05
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Vassilicos, John Christos
Sponsor
Fundacao para a Ciencia e a Tecnologia ; Programa Operacional Potencial Humano ; Fundo Social Europeu
Grant Number
SFRH/BD/61223/2009
Publisher Department
Aeronautics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)