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In turbulence theory, the application of RG is essentially a simple iterative procedure, involving the elimination of the highest wavenumber modes (corresponding to the smallest eddies) and the replacement of their mean effect upon the remaining modes by a small increment to the viscosity. The resulting equation is then rescaled so that it is defined on the same wavenumber interval as the original equation and the procedure repeated until the rescaled equation is identical upon successive iterations. This is referred to as the fixed point of the RG calculation and has recently been shown to correspond to the onset of Kolmogorov k-5/3 scaling of the energy spectrum - in addition we also obtain a universal form for the effective viscosity which takes into account all the eliminated modes. Although this procedure is appealingly simple it has been difficult to implement in practice. A recent advance has, however, been provided by the use of a rigorous conditional average in conjunction with the introduction of a model field which may be related to the actual velocity field via a perturbation expansion. This calculation re-derives the earlier published results of McComb and Watt [Phys. Rev. A. 45, 3507 (1992)] whilst providing a more sound mathematical foundation for both the treatment of errors and the introduction of approximations within the calculation. Computations based on this method give both a good prediction for the Kolmogorov constant and provide a viscosity model for our ongoing research on large eddy simulations of turbulence. Group contacts: |             
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