Particle dispersion and particle velocities were measured with laser sheets and a position sensitive photomultiplier tube to track particles. Monodisperse hexadecane droplets were injected onto the centerline of 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 jet exit velocity and nozzle diameter. Nozzle diameters of 7 and 12.6 mm were used. Reynolds numbers were in the range of 10 000-32 400. Two different droplet diameters were used viz., 60 and 90 μm. A significant range in the Kolmogorov, turbulent, and acceleration Stokes numbers was covered. The times-of-flight were used to analyze the dispersion measurements in terms of Lagrangian statistics. Dispersion data at long times of flight for a range of nozzle diameters, particle diameters and exit velocities were analyzed to obtain the Lagrangian particle diffusivity. The non-dimensional diffusivities or Peclet numbers were found to approach a value that was similar to the Eulerian Peclet number for scalar transport in a jet. Furthermore, the particle dispersion increased linearly with time at long times from their release in the jet.
ASJC Scopus subject areas
- Fluid Flow and Transfer Processes
- Mechanical Engineering