Viscous Flow Computations On Propulsors - Verification, Validation And Scale Effects

In this paper, viscous flow calculations using CFD code ReFRESCO are shown for three propulsors in open-water configuration: the INSEAN E779A propeller; a modern skewed propeller; and a ducted propeller. Verification and validation is performed as well as comparison with potential-flow methods. The results show that in all cases the trend for thrust, torque and open-water efficiency is well captured. Thrust and torque values for all propellers deviate within 2- 3% around design condition compared to experiments and are mostly within 5% for off-design conditions. A verification study for the E779A propeller shows that the numerical uncertainty for thrust and open-water efficiency is in the order of 4% and 3% for the torque. A validation analysis shows that ReFRESCO results for the open-water coefficients are validated at a level of 5%. The best results are obtained for the skewed propeller. The flow field around the ducted propeller revealed to be complex, since the shear layers (boundary-layer, tip and blade-root vortices, slip-stream and wake) of the blades, duct and hub interact with each other. For this case, model and full scale calculations are performed. For full scale, all open-water coefficients increase: propeller thrust, duct thrust, propeller torque and total open-water efficiency. The gains in efficiency are between 4 and 10%, the highest values occurring for the lowest loadings.