PROPAGATION OF GRID TURBULENCE IN HOMOGENEOUS FLUIDS

The purpose of this paper is to present the results of a laboratory ex periment dealing with one-dimensional propagation of a turbulent front induced by an oscillating grid in a homogeneous fluid. The symmetrica l quadrupolar mode of the flow, induced by the grid elements, was stud ied in the range KC=4-45, S=1-20 (KC is the Keulegan-Carpenter number, S is the Stokes number). It is shown that the depth H of the turbulen t layer increases with time t as H proportional to t(1/2). Experimenta l data for different grid parameters and oscillation amplitudes and fr equencies are presented in the nondimensional form h=const tau(1/2), u sing nondimensional depth h of the turbulent layer and nondimensional time tau. A semiempirical model is presented to explain this behavior. This model is based on the properties of a flow induced in a visous f luid by localized forcing of a line force dipole (force doubler). (C) 1996 American Institute of Physics.