Two-Dimensional RANS simulation of Flow Induced Motion of Circular Cylinder with Passive Turbulence Control.

Abstract

Passive Turbulence Control (PTC) in the form of selectively distributed surface roughness is used to alter Flow Induced Motion (FIM) of a circular cylinder. Recent de-velopments in the Marine Renewable Energy Laboratory (MRELab) on PTC of spring-mounted rigid circular-cylinders have improved dramatically the hydrodynamics of hy-drokinetic energy harnessing. In the present study, 2D-RANS with the Spalart-Allmaras turbulence model is used to simulate flow past a circular cylinder undergoing FIM trans-versely to the flow. Flow simulation is performed using a special flow solver built upon the OpenFOAM. The governing equations are solved numerically with a finite volume discretization method. Gaussian integration with a linear interpolation scheme is selected for spatial terms and a backward Euler scheme is used for time integration. The momen-tum equations are solved in a segregated manner, and the pressure and momentum va-riables are coupled using a PISO algorithm. Roughness parameters model accurately the PTC applied in the corresponding model tests. Sand paper attached to the cylinder wall is modeled as part of the body geometry. The sand grit effect is taken into account in the wall function as boundary conditions. Series of cases with different system parameters (spring constant, damping) are simulated and the results are compared with experiments. Amplitude ratio (A/D) curves show clearly 3 different branches: the VIV initial branch, the VIV upper branch, and a galloping branch, similar to those derived experimentally. Frequency, vortex pattern, transition and lift are also investigated and provide good agreement with experiments. The system parameters: Mass ratio 1.88, damping ratio ζharn 0-0.12, and spring constant 1,200 – 2,000 N/m. Re ranges from 30,000 to 130,000. The effect of system damping, stiffness and placement angle are further studied. FIM en-hancement and suppression in various zones are investigated under the guidance of PTC-to-FIM map. The phase angle by which the lift force leads the displacement is found to have a major effect on determining the FIM behavior in different zones. 2D-RANS simu-lation of cylinder flows for Re>10,000 is challenging. Nevertheless, with proper modeling of PTC, 2D-RANS simulations exhibit several of the salient features of experiments and can provide complementary flow information.