水平流动边界层内气固相间作用的试验研究

EXPERIMENTAL INVESTIGATION ON INTERACTIONS BETWEEN PHASES IN GAS-SOLID HORIZONTAL BOUNDARY LAYER

应用三维粒子动态分析仪（threedimensionalparticledynamicsanalyzer），测量了含有230μm颗粒的气固两相水平流的特性，特别是壁面边界层内的两相流动特性．结果表明颗粒载荷比（质量流率）对相间作用有较大影响，随颗粒流率的增加颗粒对气流平均速度和湍流的影响增大，颗粒使气流速度边界展变薄．颗粒和气流相互作用在不同方向上呈各向异性，颗粒对气流垂直方向的脉动影响较大．颗粒与湍流边界层气流的作用行为大致可以分成三个区域：贴壁区、中间区和外流区．

In this paper the interactions between air flow and particles have been investigated with a three dimensional particle dynamics analyzer (PDA) for the gas-solid two-phase flow in a horizontal boundary layer. The mean velocity and the statistics of turbulence fluctuations for both phases in the steamwise and the vertical direction were obtained simultaneously. Effects of particles with nominal diameter of 230μm at two different particle mass loading ratio, 1.8%and 24%, on the air flow boundary layer were examined. The turbulence modification due to the addition of particles was compared at two cross-sections along the flat plate, which was used to develop the boundary layer.The experimental results show that the particles have significant effects on the statistic characteristics of the boundary layer. Different interaction features are shown at the two different cross-sections, with x = 100mm and x = 700mm, from the front sharp tip. Though the mean velocity of the air flow was not distinguishably changed, augments in the Root Mean Squared fluctuation velocity were observed in both directions at the 100mm cross-section under the low load ratio condition, but not the case at the 700mm section. At the x = 700 mm location, attenuation effects were detected in both directions, the streamwise and the vertical direction. The augments of fluctuation at the front cross-section, which is opposite to that at the 700 mm location, may be due to the considerable fluctuation in the particle concentration. As the particle mass loading ratio is increased, the modification effects on turbulence in the boundary layer will be more significant.In the case of high load ratio, the change of turbulence in the vertical direction is more considerable than that in the streamwise direction.The particle/turbulence interaction behavior can be demarcated into three regions: the near wall region, the intermediate region and the outer region. In the region adjacent to the wall,increases in the bulk velocity and the fluctuation were detected, with evidence in the velocity and the concentration of the particles in the area. The particles are moving faster than the air and the particles airs denser near the wall. In the region above the near wall region, the lowest turbulence was located. Out of the boundary layer, the influences of particles on the fluid are not as significant as those in the intermediate region.In the paper, the behaviors of particles in the boundary layer regarding the slip velocity, the particle Reynolds number and the Stokes number are also discussed.