Particle size and velocity discrimination in a sediment-laden turbulent flow using phase doppler anemometry

A series of experiments were performed in a mixing box in order: (1) to investigate the applicability of phase Doppler anemometry (PDA) to discriminate fluid and sediment particle sizes and velocities in sediment-laden turbulent flows; and (2) to relate the size and amount of sediment in suspension to the grid-generated turbulence. Natural impurities within the water provide excellent “seeding” to represent the fluid and can be easily discriminated from spherical glass beads (75-355 µm) used as sediment. Slight asphericity in the glass beads results in larger grain size ranges determined by PDA compared to the nominal sieved sizes. The mean, root-mean-square and skewness of the vertical fluid velocities increase at higher grid oscillation frequencies but decrease with distance from the grid. Similarly, the size and amount of suspended sediment increase with grid oscillation frequency and decrease with distance from the grid. The suspension of sediment is shown to be dependent on the magnitude and anisotropy of the fluctuating vertical component of velocity. Phase Doppler anemometry offers a unique methodology to investigate the complex links between the transport of sediment and the turbulent flow field.