Effect of Dispersed Phase on Modification of Turbulent Flow in a Wall Jet

Abstract

The interaction between dispersed particles and fluid turbulence for a vertical down-flow turbulent wall jet embedded in a uniform stream was investigated experimentally and numerically. Three kinds of size classified spherical particles, which were smaller than the Kolmogorov lengthscale of the flow, were dispersed in the jet upstream of the test section. The particle mass loading ratios were set at up to 0.3. Particle and gas-phase velocities were measured by laser Doppler velocimetry with particle size discrimination, and numerical simulations were carried out considering momentum exchange between both phases. Motion of small particles with Stokes number of around unity was influenced by strong shear in the developing region. Streamwise turbulence intensity was strongly attenuated by the addition of particles in the free shear layer region, while transverse turbulence intensity was suppressed in the fully-developed region of both the free and wall shear regions. Modifications of the mean fluid velocity by the particles induced reduction in the Reynolds stress, which alters the turbulence production. Turbulence modification by particles, with Stokes number of order of unity, is due primarily to the extra dissipation which is a function of particle mean concentration and fluid turbulence in the fully-developed region.