Unformatted text preview: s vice versa. Usually it happens when one studies a new
phenomenon and only at a later stage, after understanding it
sufficiently, it is classified it, finds its proper place in the existing
theories and eventually the most reasonable definition is chosen.
Though turbulence in not a new field the above is so much true of
turbulence (there is no theory so far). This time has not yet come. # … we should not altogether neglect the
possibility that there is no such thing as
'turbulence'. That is to say, it is not meaningful
to talk of the properties of a turbulent flow
independently of the physical situation in
which it arises. In searching for a theory of
turbulence, perhaps we are looking for a
chimera.. SAFFMAN 1978
# Turbulence was probably invented by the
Devil on the seventh day of Creation when the
Good Lord wasn't looking. BRADSHAW 1994 A LIST OF
Mentioned and not mentioned in
previous lectures. Some to be discussed
in more detail in January – March 2008 Statistical' and `structural' contrapose each other
# Turbulence is nearly Gaussian and/or possesses a random (quasi)Gaussian background
# Kolmogorov picture is structureless and quasi-Gaussian
# Large scales and small scales are decoupled.
# Turbulence can be described adequately by equations ‘simpler’ than
the Navier-Stokes equations, e.g. by a low dimensional system.
# ‘Eddy viscosity' and ‘eddy diffusivity' explain the enhanced transfer
rates of momentum, energy and passive objects.
# Spatial fluxes represent ‘cascade' in physical space.
# At large Re the ratio of non-linear and the viscous terms is large.
# # Vorticity amplification is a result of the kinematics of turbulence, i.e.
# Vortex lines are on average stretched rather than compressed.
because two particles on average move apart from each other.
# When Re is large vorticity is virtually frozen into the fluid.
# The vorticity intensification process is the strongest where vorticity
already happens to be large....
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