A note on the numerical simulations of flow past a wavy square-section cylinder

The flow past a square-section cylinder with a geometric disturbance is investigated by numerical simulations. The extra terms, due to the introduction of mapping transformation simulating the effect of disturbance into the transformed Navier-Stokes equations, are correctly derived, and the incorrect ones in the previous literature are pointed out and analyzed. Furthermore, the relationship between the vorticity, especially on the cylinder surface, and the disturbance is derived and explained theoretically. The computations are performed at two Reynolds numbers of 100 and 180 and three amplitudes of waviness of 0.006, 0.025 and 0.167 with another aim to explore the effects of different Reynolds numbers and disturbance on the vortex dynamics in the wake and forces on the body. Numerical results have shown that, at the mild waviness of 0.025, the Kairmain vortex shedding is suppressed completely for Re = 100, while the forced vortex dislocation is appeared in the near wake at the Reynolds number of 180. The drag reduction is up to 21.6% at Re = 100 and 25.7% at Re = 180 for the high waviness of 0.167 compared with the non-wavy cylinder. The lift and the Strouhal number varied with different Reynolds numbers and the wave steepness are also obtained.

Experimental investigation of the flow-induced motion of a square-section cylinder

The flow-induced motion(FIM)of an elastically mounted square-section cylinder is experimentally investigated over a wide range of Reynolds numbers(1.5×10^(4)<Re<7.0×10^(4)).A 14 mlong towing tank water channel and a carrier are designed to facilitate the investigation of FIM at high velocities.The cylinder is limited to a transverse oscillation and is carried inside the water channel.The effect of cylinder orientation on FIM is studied by performing experiments for two angles of attack(45°and 0°).The experiments are performed for two different spring stiffness to consider the influence of the natural frequency on the response of the system.Since the water has been allowed to stay calm between the tests,experiments are conducted with zero disturbance of the fluid flow around the cylinder.The experimental setup has shown promising results for a circular cylinder in our previous studies.The results for the diamond cylinder(square-section cylinder with a 45°angle of attack)indicate that FIM only consists of vortex-induced vibration(VIV)and the oscillation in the upper branch occurs in a wider range of reduced velocities compared with the circular cylinder.It can be concluded that a diamond cylinder is a better option for having synchronization in a wider range of water velocities for the purpose of energy extraction in VIV-based ocean energy conversion devices.