Dense-Spray Properties: Structure and Turbulence Modulation.

摘要

A theoretical and experimental study of aspects of dense sprays is described, considering: the structure and mixing properties of the near-injector, dense-spray region of pressure-atomized sprays; and the direct effect of particle (drop) motion on the turbulence properties of multiphase flows (which is often called turbulence modulation). The structure of dense sprays was studied using large-scale (9.5 and 19.1 mm jet exit diameters) water sprays in still air. Measurements included: flow visualization using flash photography; liquid volume fractions using gamma-ray absorption; streamwise mean and fluctuating velocities at the injector exit, and entrainment velocities, using laser velocimetry; and dispersed-phase properties using single- and double-flash holography. Predictions based on the locally-homogeneous flow (LHF) approximation of multiphase flow theory were evaluated using the measurements. Measurements showed that mixing was strongly influenced by the degree of flow development at the injector exit and the breakup regime: fully-developed flow and atomization breakup yielded the fastest mixing rates. Turbulence modulation was studied by considering nearly monodisperse spherical glass particles falling in a stagnant water bath, where effects of turbulence modulation were responsible for the entire turbulence field. Measurements included phase velocities, as well as the temporal and spatial correlations of continuous-phase velocities, using a two-point phase-discriminating laser velocimeter; and calibration of particle motion properties using motion-picture shadowgraphs. (JHD)