Incompressible SPH simulation of flow past a horizontal cylinder between plane wall and free surface

Flow past a circular cylinder located between free-surface and wall boundaries is modelled numerically using non-uniform particle size incompressible smoothed particle hydrodynamics (SPH). Several enhancements including Rhie and Chow interpolation, colour function-based free surface tracking, and modified particle shifting are introduced to increase the accuracy and efficiency of the method. A parameter study at constant Reynolds number, Re=150, examines the influence of Froude number (Fr=0.2−0.6), submergence ratio (H∕D=0.5−1.0, where H is the distance between the apex of the cylinder and undisturbed free surface, and D is the cylinder diameter), and bottom gap ratio (G∕D=1.0−5.0, where G is the distance between the base of the cylinder and the bed) on the ambient free-surface flow pattern and hydrodynamic force on the cylinder. It is found that the vortex shedding pattern depends on all three parameters. As the Froude number increases for fixed submergence ratio and bottom gap ratio, vortex shedding is eventually suppressed. As the submergence and bottom gap ratios increase, the threshold of vortex shedding suppression shifts to higher values of Froude number. The mean drag coefficient depends on the submergence ratio and bottom gap ratio but is independent of Froude number. Meanwhile, the lift coefficient depends on submergence ratio and Froude number but is independent of bottom gap ratio. Spectral analysis of force and free-surface elevation time signals shows that the free-surface deformation and lift force are closely related during the vortex shedding regime

DFIB-SPH study of submerged horizontal cylinder oscillated close to the free surface of a viscous liquid

The hydrodynamics is studied numerically of a horizontal cylinder undergoing forced in-line oscillation beneath the free surface of otherwise quiescent liquid at low Keulegan-Carpenter and Froude numbers. The direct forcing immersed boundary-smoothed particle hydrodynamics (DFIB-SPH) numerical model uniquely combines two well-established techniques: The direct forcing immersed boundary method and SPH. This facilitates accurate evaluation of the potentially violent free surface motions through SPH and the hydrodynamic force on the solid body using a volume integral. A parameter study is conducted covering a range of Keulegan-Carpenter numbers (KC = 3, 7, and 10) and submergence ratios () at fixed Reynolds number (Re = 100) and Froude number (Fr = 0.35). The flow pattern and transverse force coefficient are found to be affected by the proximity of the cylinder to the free surface. Spectral analysis suggests that free surface wave motions are linked to the transverse force acting on the submerged, oscillating cylinder

Numerical investigation of the effects of a small fixed sphere in tandem arrangement on VIV of a sphere

A direct-forcing immersed boundary (DFIB) method with a virtual force is used to investigate the vortex-induced vibration (VIV) of an elastically mounted sphere in uniform flow at a moderate Reynolds number. A novel method is investigated to control VIV of an elastically mounted sphere by placing a small fixed sphere inline in tandem arrangement. The numerical method is validated by comparisons with previously published results for flow past a stationary sphere and for VIV phenomena. The influence of the small sphere diameter and the gap between the spheres on VIV are studied through an analysis of the hydrodynamic force coefficients, sphere responses, vortex shedding modes and energy efficiency. Regression analysis is conducted to propose mathematical relations for estimating the maximum values of hydrodynamic force coefficients and amplitude ratio. This study proves the capability of the DFIB model for investigating VIV of a sphere. It is also found that the small fixed sphere upstream increases the lift coefficient and amplitude ratio of the vibrating sphere while the drag coefficient is reduced. Furthermore, the energy efficiency of VIV of the sphere is found to be increased by up to three times due to the upstream small fixed sphere