Mehmet Meric Hirpa
A large-scale 9 m long horizontal flow loop equipped with a non-intrusive laser-based particle image velocimetry (PIV) system was used to carry out bed erosion experiments with water and viscoelastic fluids. Also, pipe flow experiments with viscoelastic fluids were carried out in this horizontal flow loop. Effect of sand particle surface characteristics on the critical velocity and the near wall turbulence characteristics of water flow in the horizontal loop were investigated by using
more » ... by using surface-treated and untreated industrial sands of four different mesh size. The PIV technique was used to determine instantaneous local velocity distribution near the stationary sand bed-water interface under sub-critical and critical flow conditions. The near wall velocity distributions determined with the measured frictional pressure loss values were then used for the evaluation of the Reynolds shear stresses, axial and radial turbulent intensities acting at the bed/water interface. Critical velocity for the onset of particle removal from the sand bed increased with the increasing particle size. When sand particles with special surface treatment were used, it was observed that the critical velocity required for the onset of the bed erosion was significantly lower than that of required for the untreated sand particles. The degree of reduction in critical velocity varied between 14 to 40% depending on the particle size. The effect of surface treatment on the transport efficiency became more significant with the decreasing particle size. Effects of sand particle size and sand surface properties on the critical velocity required for the onset of the bed erosion and the near-wall turbulence characteristics of the polymer fluid flow over the sand bed in the horizontal pipeline were studied experimentally. Industrial sand particles having three different size ranges with and without special surface treatment were used in this experimental study. The instantaneous local velocity distributions and near wall turbulence characteristics (such as Reynolds stress, axial and turbulence intensity profiles) of dilute polymer fluid flow over the stationary sand bed under turbulent flow conditions were determined by PIV technique. The critical velocity for the onset of the particle removal from a stationary sand bed using a polymer fluid flow is affected by the sand particle size and the surface characteristics, however, the iii effect was not straightforward, and it was varied depending on the relative comparison of the sand particle size with respect to the thickness of the viscous sublayer under turbulent flow condition. An experimental study was conducted to investigate how the fluid elastic properties would influence, the frictional pressure drops, the critical velocity for the onset of the bed erosion, and turbulent flow characteristics (i.e. Reynolds stress, axial and radial turbulence intensity profiles) of the polymer fluid flow over the stationary sand bed deposited in horizontal pipeline. Polymer fluids were prepared by mixing three different grades (i.e. 5x10 5 , 8x10 6 , 20x10 6 g/gmol) of partially hydrolyzed polyacrylamide (HPAM) polymer. These polymer fluids, which had almost identical shear viscosity characteristics while showing significantly different elastic properties, were used together with 30/50 mesh size industrial sands in the bed erosion experiments. After determining the critical velocities for the onset of the bed erosion using both fluids, the frictional pressure drops at critical and several subcritical velocities were recorded for both fluids. Results showed that the fluid elasticity affects the bed erosion dynamics significantly. Generally, frictional pressure drops, and critical velocities for the bed erosion all increased with the increasing fluid elasticity. Three polymer fluids were prepared by mixing three different grades of HPAM polymer and these fluids, having the same shear viscosity but different elasticity, were used for the experiments. By using these fluids, we were able to investigate the direct effect of the fluid elasticity on drag reduction and the onset of the turbulence in horizontal pipe flow. Results showed that that drag reduction associated with the pipe flow of a dilute polymer fluid was enhanced by the increasing the fluid elasticity. Moreover, the fluid elasticity was effective in controlling the onset of the turbulent flow. An earlier transition to turbulent flow regime (as compared to water flow) was only observed during the flow of the most elastic fluid. Drag reduction started to be effective at a Weissenberg number around 2 and it increased with increasing Weissenberg number. iv
doi:10.7939/r3-f0e9-z293 fatcat:bxqpdq3d25ecvfwbauyzheb6ni