Usually it happens when one studies a new phenomenon

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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 MISCONCEPTIONS MISCONCEPTIONS Mentioned and not mentioned in Mentioned 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. Vortex 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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