Our customer is one of India’s foremost designers and manufacturers of naval vessels. During the design of one ship, customer was fitting a harmonically oscillating hydrofoil wing to the vessel to control it. It was required to estimate the hydrodynamic characteristics of the hydrofoil to estimate the effect of oscillation on control of the vessel. Simulations were carried out at various vessel speeds and angular speeds of the hydrofoil.
Zeus Numerix carried out a systematic study with 2D and 3D analysis of the problem statement using both the steady and unsteady approaches. Hydrofoil is located on one side of the ship, hence the ship was ignored in simulation and the hydrofoil root ended in a flat plate. Angle of attack (AoA) attained due to the oscillation went up to 35 deg on both sides. Results were compared with literature and it was found that the results were in good agreement till 15 deg. The simulations gave oscillatory forces and moments at higher angles of attack and the mean values gave higher prediction of drag and lift as compared to experiment.
Several eddies and separation were seen in the simulation at high AoA and vessel speeds. Customer was given the locations of possible cavitation during the upstroke and down stroke for these cases. The design had chord length and wing length as approximately equal the design suggestions were given to increase the length to get more lift and reduce the high AoA requirement. Bounds of error due to the unsteadiness were reported. Hysteresis effect on lift during the upstroke and down stroke was also given as a result. Customer used the results for structural design and controls.