Abstract:

The particle image velocimetry (PIV) is used to conduct experimental research in the solid-liquid two-phase plane turbulent boundary layer. The turbulence statistics such as the average velocity profile, turbulence intensity and Reynolds stress of the particle phase and single-phase clean water are compared to analyze the behavior of the particles in the turbulent boundary layer. The concept of multi-scale spatial locally-averaged vortices is utilized to extract the spatial topologies of the spanwise vortex head and the statistic of the prograde vortex is acquired. From that, the spatial topologies of the fluctuating velocity and streamlines around the prograde vortex at different normal positions can be obtained. The degree of development of the prograde vortex and the surrounding turbulence coherence structure can be compared and analyzed. The results show that compared with the clean water conditions, the buffer layer of the turbulent boundary layer of the particle phase becomes thinner, the logarithmic region moves downward, the turbulence intensity is enhanced, and the Reynolds stress in the logarithmic law region is increased. The fluctuating velocity of the particle phase is different from the clear water condition around the vortex, and the particles can be effectively transferred by the burst process around the spanwise vortex. The particle-laden flow has a large prograde vortex core and develops as the normal position rises. The vortex and the band stretch longer in the flow direction. At the same time, it is found that there is always a retrograde vortex in the lower left of the prograde vortex under both conditions, and the formation of retrograde vortex in the particle-laden flow is weaker than that of single-phase fluids. The number of prograde vortices in both conditions decreases with the increase of the normal position, and finally gradually stabilizes.

Key words: two-phase flow|PIV|turbulent boundary layer|multi-scale spatial locally-averaged vortices|prograde vortex