An approach for estimating seetling velocity in turbulent flows

Abstract

Precise estimation of the settling velocity of particles in turbulent flows is required for many engineering applications including modeling of the transport of suspended sediments and the transport of particle pollutants. This study attempts to quantify the turbulence from direct measurements at a reservoir and presents an approach for estimation of settling velocities of suspended sediments modified by the quantified turbulence. A novel application of acoustic Doppler instruments for measurement of settling velocities was presented considering the fact that settling velocity of particles are commonly estimated indirectly from the balance of settling and diffusive gradients. In the present study, synchronized 3-D velocity and temperature time series were monitored at Tahtali Reservoir in Turkey where the data were utilized to characterize the turbulence characteristics by various means (i.e. buoyancy flux, Richardson flux and Stokes number) provided in the literature. Stokes' settling velocities modified by the turbulent characteristics were compared with the measured settling velocities to discuss which parameters have the greatest impact on the settling mechanism and need to be considered in the presented approach. The results of the study revealed that, when production of turbulence was high, modified settling velocities matched the monitored velocities better. So; it was concluded that modification of Stokes' settling velocities by turbulent kinetic energy production profiles performs better for high turbulent conditions.