Experimental Investigation on Turbulence Modulation in the Boundary Layerof a Horizontal Particle-laden Channel Flow with Relative Low Mass Loading Ratios

摘要

The turbulence modulations were experimentally investigated in the lower boundary layer of a fully developed horizontal channel flow. Polythene beads with diameters of 60um and 110um were used as dispersed phases, respectively. The particle mass loadings examined presently were 0, 2.5 × 10~4, 1 x 10~(-3) and 5 × 10~(-3). The corresponding volume fractions were 0, 2.85× 10~(-7), 1.14 × 10~(-6) and 5.7 × 10~(-6).All experiments were performed at a wall Reynolds number of Re_τ=444, based on wall shear velocity u_τ=0.445m/s and half channel height h=0.015m. The corresponding Reynolds number, based on the mean velocity and half channel height, Re_h=6379. A simultaneous two-phase PIV measurement technique was adapted to acquire the turbulent statistics quantities for both gas and particle phases, and examine the coherent structures in the near-wall region. It is found that the presence of particles significantly modifies the turbulence of gas phase, even when the mass loading were at the order of 10~(-4). In the present low-mass-loading experiment, the velocity fluctuations of gas phase in both the streamwise and wall-normal directions and the shear Reynolds stress all considerably decreased in the lower boundary layer, excepting the velocity fluctuations of the streamwise component increased slightly in the near-core region (y~+>100). The reduce of gas phase two-point correlations of both streamwise and wall-normal fluctuation velocities pointed out that the addition of particle resulted in weaker coherent structures in the turbulent boundary layer, with shorter streamwise extent of the quasistreamwise structures.