Experimental Study of Fluid Flow through Model Fractures, No.2 Cylindrical Contact Areas

Abstract

The pressure drop through model fractures with cylindrical contact areas has been studied experimentally. The model fractures are made of two parallel acrylic plates whose dimensions are 2m (length)×0.44m (width), and the created aperture has a dimension of 2mm, which is common to all model fractures. In the mid portion of the opening space (0.8m in length), the cylindrical obstacles, whose diameters are 120mm, 40mm and 20mm, are glued between the acrylic plates. The water is pumped up from the reservoir and led to one end of the model fracture. The pressure drops along the flow direction are monitored. The nature of water flow in the model fracture, for example laminar or turbulent, is also determined by using the streakline visualization technique and the laser Doppler velocity meter. Experimental results show that the line of friction coefficient A plotted vs. Re, is parallel to 96/Re for Re<100, but deviates from this line for Re>600. This means that the shear stress of the parallel plate walls governs the phenomena at low velocities. In other word Darcy's law is a good approxima tion model for predicting the pressure drop of model fractures at low velocities if the aperture depth is replaced by a hydraulic mean depth. In contrast at high velocities, the drag force of cylinders becomes strong, and the pressure drop is controlled mainly by the force. The pressure drop predicted by the presented model which is expressed by the combination of the shear stress and the drag force, agrees well with the experimental data over all Re region.