Free decay of turbulence and breakdown of self-similarity

It has been generally assumed, since the work of von Karman and Howarth in 1938, that free decay of fully-developed turbulence is self-similar. Here w e present a simple phenomenological model of the decay of three-dimensional incompressible turbulence, which predicts breakdown of self-similarity for low-wavenumber spectral exponents n in the range n(c) < n < 4, where n(c) is some threshold wavenumber. Calculations with the eddy-damped quasi-norma l Markovian approximation give the value as n(c) approximate to 3.45. The e nergy spectrum for this range of exponents develops two length-scales, sepa rating three distinct wavenumber ranges. [S1070-6631(00)02603-9].