Kármán-Howarth closure equation on the basis of a universal eddy viscosity.

This Rapid Communication presents a simple closure for the two-point correlation transport equation in decaying isotropic turbulence. It relies essentially on an eddy viscosity ν(t) which exhibits some remarkable universal facets over an impressively wide range of scales. This allows us to model the third-order structure functions in different decaying flows covering a large extent of Reynolds numbers. The model is numerically time integrated to predict the decay of second-order structure functions and compared to experiments in grid turbulence. Agreement between predictions and measurements is satisfactory.