Hydrodynamic Performance Analysis of a Collective and Cyclic Pitch Propeller under Bollard Pull Condition through Numerical Evaluation of Two-Dimensional Pitching Hydrofoils

Propulsion and maneuvering of autonomous underwater vehicles require a combination of effective and efficient operation at both high and low speeds. The collective and cyclic pitch propeller (CCPP) is a novel system designed to provide the required operational flexibility through control of the propeller's blade pitch. Collective pitch control governs the forward generated thrust, whereas cyclic pitch control governs the generated maneuvering force(s)/side-force(s). In this article, a numerical analysis into the CCPP's hydrodynamic performance at bollard pull is set-up, reducing the complex three-dimensional flow problem to a two-dimensional problem. Through a force break-down model, the CCPP's hydrodynamic performance is related and matched to the operation of a pitching hydrofoil. Analysis of the two-dimensional numerical results can thereby provide insights into the performance of the three-dimensional CCPP. First, the performance of the pitching hydrofoils is investigated as such, relating the generated lift, drag, and moment to the occurrence of dynamic stall. Next, the methodology's applicability and limitations are discussed by comparing the umerical results with recent experiment CCPP work to allow the model to be used for a numerical evaluation of the CCPP's performance. Under the evaluated conditions, testing a range of collective and cyclic pitch angles under bollard pull, the side-force generation by the CCPP is shown to be highly dependent on the generated drag force at higher collective pitch angles. At low pitch angles, the side-force generation is controlled by the lift produced over the pitching blades, and efficient but not highly effective. As the collective pitch is increased, the generated drag affects both the effectiveness of the side-force and the side-force efficiency, defined by the large resulting side-force orientation. At larger collective pitch angles, the lift forces are overtaken by the drag generation, resulting in effective but inefficient side-force generation.