title: Structure function of passive scalars in two-dimensional turbulence.
abstract: The structure function of a scalar theta(x,t), passively advected in a two-dimensional turbulent flow u(x,t), is discussed by means of the fractal dimension delta1g of the passive-scalar graph. A relation between delta1g, the scaling exponent zeta(theta)(1) of the scalar structure function D1(theta)r, and the structure function D2(r) of the underlying flow field is derived. Different from the three-dimensional (3D) case, the 2D structure function also depends on an additional parameter, characteristic of the driving of the passive scalar. In the enstrophy inertial subrange a mean-field approximation for the velocity structure function gives a scaling of the passive scalar graph with delta1g<2 for intermediate and large values of the Prandtl number Pr. In the energy inertial subrange a model for the energy spectrum and thus D2(r) gives a passive-scalar graph scaling with exponent delta1g=5/3. Finally, we discuss an application to recent observations of scalar dispersion in nonuniversal 2D flows.
authors.affiliation: Fachbereich Physik, Philipps-Universität Marburg, D-35032 Marburg, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Eckhardt
authors.forename: J
authors.initials: J
authors.lastname: Schumacher