Turbulence structure of dispersed two-phase flows (measurements by laser techniques and modeling)

Development of measurement techniques and numerical simulations gives further insights into understanding turbulence structure of dispersed two-phase flows. The present paper describes investigation of Eulerian particle-turbulence interactions preformed by using laser Doppler velocimetry (LDV) and digital particle image velocimetry (DPIV). Langrangian DPIV measurements are also described. The results are compared with turbulence models based on the multiple time scale concept. Laser Doppler velocimetry (LDV) has been the instrument of choice for measuring dispersed- and gas-phase velocities in particle-laden flows. LDV was used for simultaneous measurements of continuous- and dispersed-phase velocities, which permits the particle size discrimination based on light scattered intensity. Digital particle image velocimetry (DIPIV) is increasingly considered a proven technique for detecting both phases simultaneously. The author's group developed measurement systems to distinguish a dispersed-phase particle from a tracer in fluid flow. Experiments in a water channel showed that fluid turbulence was augmented by particles, which are comparable to or slightly larger than the Kolmogorov lengthscale of the flow. The above experimental results support the idea that several time scales are needed for modeling. The present model (multiple-time-scale) divides the energy containing part of the spectrum into two regions, "production" and "transfer" regions. This model has succeeded in predicting channels flows and wall and confined jets laden with particles. The author's group has developed Lagrangian measurement methods by DPIV and a CCD camera mounted on a moving shuttle with the mean streamwise velocity of the particles in a downflow water channel. This allows the particle dynamics to be investigated and the exact forces acting on a particle to be determined.