Turbulence Spectrum Around a Suspended Cylinder with Vertical Endplate Effects to Enhance VIVACE Strength

Abstract

Alternating vortex formation on a horizontal suspended cylinder depends largely on flow turbulence causing its vibration. This vibration is known as “vortex-induced vibration” that leads to a power-harnessing device such as VIVACE, which was usually tested for high velocities (>1.3 m/s) and minimum 0.8 m flow depth. The present research provides feature flow field analysis around such VIVACE-like structures at only 0.17 m shallow waterway with a much lower velocity of ∼0.59 m/s. However, synchronization does not occur at such low water depth using a suspended cylinder only. Therefore, to overcome these conditions, behind that suspended cylinder of 0.04 m diameter (D), a 1.25D-wide vertical endplate was placed. The endplate was sensibly used here to further strengthen the induced vortex. Detailed analysis of the turbulent flow behaviors was done for different cylinder positions D/2, 1D, 3D/2, and 2D and locating the vertical endplate 2.25D away. The turbulence spectrum characteristics were studied from 3D velocity components, velocity vectors, Reynolds shear stresses, turbulence intensities, turbulence kinetic energy (TKE), its dissipation rate, and vorticity. The shear effect on the approach flow was inspected for different flow separation angles. The statistical parameters of velocity fluctuation moments of third-order skewness and TKE fluxes for longitudinal and vertical velocity were calculated in different lengths from the vertical endplate. Flow separation can be visualized from the three-directional velocity contours. Alternating vortex formation is identified from vorticity contours. The best vertical position of the cylinder was identified for which the induced vibration effect is enhanced for the combined effect of wake and horseshoe vortices developing between the cylinder and plate. This setup may be utilized as a hydrokinetic device similar to VIVACE in harnessing power from shallow waterways.