Influence of Inertial Particles on Turbulence Characteristics in Outer and Near Wall Flow as Revealed With High Resolution Particle Image Velocimetry

摘要

A fully developed turbulent particle-gas flow in a rectangular horizontal channel 100 x 10 x 4000 mm(3) is disclosed with high spatial resolution two-dimensional (2D) particle image velocimetry (PIV). The objective is to increase the knowledge of the mechanisms behind alterations in turbulent characteristics when adding two sets of relatively large solid spherical particles with mean diameters of 525 and 755 mu m and particle size distributions of 450-600 and 710-800 mu m, respectively. Reynolds numbers are 4000 and 5600 and relatively high volume fraction of 5.4 x 10(-4) and 8.0 x 10(-4) are tested. Both the near wall turbulent boundary layer flow and outer core flow are considered. Results show that the carrier phase turbulent intensities increase with the volume fraction of the inertial particles. The overall mean flow velocity is affected when adding the particles but only to a minor extent. Near the wall, averaged velocity decreases while fluctuating velocity components increase when particles are added to the flow. Quadrant analysis shows the importance of sweep near the wall and ejection events in the region defined by y(+) > 20. In conclusion, high inertia particles can enhance turbulence even at relatively low particle Reynolds number < 90. In the near bottom wall region, particles tend to be a source of instability reflected as enhancement in rms values of the normal velocity component.