DRAG FORCES ON A SOLID BODY IN DRY SEDIMENT AND SEDIMENT-WATER MIXTURE FLOWS

Experiments of drag forces on a solid body in dry sediment and sediment-water mixture flows are made. The measurements of the drag forces show their significant variation with time. The forces are divided into a mean value and fluctuations. From the mean value a drag coefficient is determined. A nondimensional parameter governing the flow situation around the body is proposed. Drag coefficient depends on the nondimensional parameter. Frequency spectra of fluctuations for the mixtures and dry sediment are compared with those for clear water. The collisions of grains with the body play dominant role for the generation of drag forces in the flows with the smaller values of the parameter. The effect of turbulence becomes important in the flows with the larger values of the parameter.