A 3D LIF system for turbulent buoyant jet flows

A Laser-Induced Fluorescence (LIF) system for mapping the three dimensional tracer concentration field in turbulent flows is described. The system is particularly suited to studies of single or multiple buoyant jets discharged into unstratified and stratified flowing environments for conditions typical of wastewater discharges into surface water bodies. A laser beam is scanned through the flow and LIF images are obtained in parallel planes with a high-speed synchronized CCD camera. Refractive index matching is used to minimize refractive index variations due to local density gradients. An application to vertical round buoyant jets discharging into unstratified and stratified cross flows is presented. The three-dimensional system can obtain vastly more data than is possible with probe-based techniques and can yield far more insight into the flow and mixing processes.Abbreviations a Combined attenuation coefficient, cm^-1 - a_w Attenuation coefficient for fresh water, cm^-1 - B Buoyancy flux of buoyant jet, cm⁴/s³ - c Tracer concentration, g/l - C _salt, C _eth Salt and ethanol concentrations, g/l - d Port diameter, cm - g Acceleration due to gravity, cm/s² - Modified acceleration due to gravity at source, cm/s² - Q Volume flux of buoyant jet, cm³/s - I Image gray scale level, DN - l _a,l _Q , l _M , l _s, l _t Buoyant jet length scales, cm (Eq. 8) - L _y Distance from camera to image plane, cm - M Momentum flux of buoyant jet, cm⁴/s² - M _y Image scale factor - N Buoyancy frequency, s^-1 - u _a Ambient flow velocity, cm/s - u _j Jet exit velocity, cm/s - P Laser power, W - S ₀ Lowest dilution on the vertical center-plane through the nozzle - S _m Minimum dilution: lowest dilution in a vertical plane perpendicular to the flow - x, y, z Coordinates, cm - z _m Maximum rise height of buoyant jets, cm - z _e Equilibrium rise height of buoyant jets, cm - Image calibration constant - ₀ Effluent density, g/cm³ - _a Ambient density, g/cm³