^{1} Risø National Laboratory for Sustainable Energy, Technical University of Denmark^{2} IT Service Department, Risø National Laboratory for Sustainable Energy, Technical University of Denmark^{3} Department of Wind Energy, Technical University of Denmark^{4} IT Service, Administration, Technical University of Denmark

Abstract:

On the basis of Corrsin’s independence hypothesis, in conjunction with specific assumptions about the form of the distance-neighbour function, an equation is derived for twoparticle dispersion in isotropic turbulence with no mean motion. It is formulated in terms of the mean-square difference between the particle positions r 1(t1) and r2(t2) at arbitrary times t1 and t2 after the release of the particles with a given initial separation. Eddy removal and eddy decay are included with wave-number dependent time scales. The equation, which in general must be solved numerically, has been considered for the scale free k−5/3 energy spectrum as well as for the von K´arm´an spectrum. The model implies that only when the outer scale is infinite, i.e. in the limit where the energy spectrum is of the form k−5/3, will there be a Cεt 3 range of the mean-square separation between the two particles. In this limiting case it is possible to estimate the dimensionless Richardson- Obukhov constant C as a function of a dimensionless eddy-decay parameter. A reasonable choice of this parameter leads to a C-value of the order 1.