Influence of cylinder rotation in close to a free surface on flow characteristics

This study investigates the numerical simulation of unsteady flow over a rotating circular cylinder near a free surface using the Volume of Fluid (VOF) method. The hydrodynamic characteristics and flow pattern are analyzed for various Froude numbers (0.3, 0.55, and 1), submergence depths (0.4, 0.6, and 1), and rotation rates (+/- 0.5, +/- 1, and +/- 2). The results indicate that both the rotation direction and rate significantly influence flow instability. Counterclockwise rotation reduces free surface instability and drag coefficient. At a rotation rate of 2, the average drag coefficient decreases by 93% compared to a stationary cylinder at Froude number 0.3. Clockwise rotation induces free surface instability and increases the lift and drag coefficients. Higher Froude numbers result in more significant free surface variations, and increased submergence depth leads to stretched vortices.