A RAYLEIGH LIGHT-SCATTERING FACILITY FOR THE INVESTIGATION OF FREE JETS AND PLUMES

A Rayleigh light scattering facility (RLSF) has been developed and successfully used to examine mixing in free jets and buoyant plumes. The RLSF couples laser diagnostics with a cylindrical clean room, test section diameter of 2.4 m and a height of 2.4 m, to monitor the real-time concentration behavior within turbulent flows. The facility has been carefully designed to minimize interferences of glare and Mie scattering by suppressing background light and removing dust particles. The relatively large working section of the RLSF allows quantitative concentration measurements via Rayleigh light scattering (RLS) in free shear flows entering quiescent surroundings. As a result, RLS measurements are now possible in momentum-driven flows for conditions which were impossible in the past and in buoyancy-driven flows for which no previous RLS investigations have been made. Initial measurements of concentration in momentum-driven jet flows of helium and Freon-13 and a transitional (momentum- to buoyancy-driven) jet of Freon-13 demonstrate the advantages of the new RLSF.