Analysis of oscillatory flow around a rigidly attached spherical particle to the bottom in a sloshing tank

Oscillatory flows are commonly observed flow conditions in sloshing tanks or at the seabed/river mouths under the effect of gravity and seiche waves. In such environments, particles are exposed to bi-directional oscillation-caused forces. These particles are usually sediments in settling basins under earthquake conditions or deposits on seabed/river mouths.

Physical model tests investigated the hydrodynamic forces acting on a spherical particle. This step is followed by a computational fluid dynamic model (i.e., RANS model), which aims to resolve the pressure and force fluctuations around a rigidly attached spherical particle to the bottom.

The experiments were conducted in a sloshing tank with 28.5cm length, 14.5 cm in width, and 20 cm in depth. A step-type-computer-controlled motor triggered the body of water within the tank. The motion of the mobile component of the tank was measured using two independent devices, i.e., an accelerometer and an ultrasonic distance sensor. The utilization of these measurement devices enables verifying the records of the motion double. Six different cases were conducted to define the error band for each device. These calibration cases emerge as a combination of the “better step motor speed” and “maximum displacement”. The acceleration records constitute a basis as an input for the RANS-based numerical model. During the validation/calibration of the CFD model, video records of the water surface observed during the experiment and the CFD outputs were comparatively analyzed based on an image-processing technique.

Once it was ensured that the CFD model simulated the sloshing process within the tank with an acceptable accuracy, a spherical particle was fixed to the bottom as the second phase of this study. Various sloshing scenarios were performed better to understand the fluctuation of the pressure field around the sphere. Based on these simulations, the variation of drag coefficient around the spherical body which emerges under the oscillatory flow was calculated.