A laser method to determine turbulent intensity using probability after-effects

Abstract

A novel way to use particle arrival statistics in two-spot laser anemometry of turbulent flow is developed. For two cylindrical scattering volumes spaced a fixed distance apart in the flow direction, a relationship between the classical 'probability after-effects function' and the mean square displacement of a fluid particle in a turbulent flow can be established. Determination of this displacement as a function of the separation of the probe centers gives a measure of the turbulent Lagrangian correlation function. Experimental measurements are given for short separation distances for turbulent flow in a submerged water jet. The turbulence intensity obtained directly from the 'probability after-effects function' agrees favorably with other laser velocity measurements. The experimental technique can be combined with a laser Doppler velocimeter to measure Lagrangian and Eulerian turbulence quantities simultaneously at a point in the flow.