PARTICLE DISPERSION IN A TURBULENT ROUND JET

Particle dispersion and particle velocities were measured with laser s heets and a position sensitive photomultiplier tube to track particles . Monodisperse hexadecane droplets were injected onto the centerline o f a turbulent air jet. Their radial dispersion, axial velocities, and times of flight were measured as functions of axial position. The time and length scales of the jet were varied through the control of the j et exit velocity and nozzle diameter. Nozzle diameters of 7 and 12.6 m m were used. Reynolds numbers were in the range of 10,000-32,400. Two different droplet diameters were used viz., 60 and 90 mu m. A signific ant range in the Kolmogorov, turbulent, and acceleration Stokes number s was covered. The times-of-flight were used to analyze the dispersion measurements in terms of Lagrangian statistics. Dispersion data at lo ng times of flight for a range of nozzle diameters, particle diameters and exit velocities were analyzed to obtain the Lagrangian particle d iffusivity. The non-dimensional diffusivities or Peclet numbers were f ound to approach a value that was similar to the Eulerian Peclet numbe r for scalar transport in a jet. Furthermore, the particle dispersion increased linearly with time at long times from their release in the j et. (C) 1998 Elsevier Science Inc. All rights reserved.