Magnitude and phase shift of the side-force generated by a collective and cyclic pitch propeller

Almost two-thirds of the earth's surface is covered by water and hidden beneath the water surface remains a vast world yet to be discovered. The high risk and dangerous nature of underwater reconnaissance has resulted in the development of a wide variety of unmanned exploration vehicles. An example of such a vehicle is the Autonomous Underwater Vehicle (AUV), a programmable submersible capable of conducting a pre-determined mission autonomously over large distances and lengths of time without the need for additional human interaction. Since the 1970s AUVs have become the preferred underwater exploration tool in many industries and fields of research, e.g. oil industry, geographical surveying, marine biology, and even military applications. Successful completion of such AUV missions requires a vehicle design that combines long-endurance travelling efficiency with effective operation at low speeds. Considering that traditional control surfaces lose their efficiency at low speeds and low speed manoeuvring aids such as side- or podded-thrusters reduce the long-endurance travelling efficiency, a design issue arises. The design trade-off between travelling range and low speed manoeuvring compromises and limits the performance of AUVs and needs to be addressed accordingly. The work outlined in this thesis investigates the hydrodynamic performance of a novel AUV propulsion and manoeuvring concept, the collective and cyclic pitch propeller (CCPP). Aimed at addressing the aforementioned design issue, the CCPP is an extension of the traditional controllable pitch propeller and applies helicopter technology to achieve advanced control of the propeller blade pitch, i.e. orientation of the blade. As such, the CCPP provides effective and efficient propulsion and manoeuvring forces for an AUV at both high and low forward velocities. The current work focused on investigating the manoeuvring or side-force generated by the CCPP. As such, the performance of the CCPP's side-force generation is quantified by both the magnitude and phase shift of the side-force. The magnitude defines the force generation's effectiveness in manoeuvring the AUV, while the phase shift, as a result from a discrepancy between the intended and resulting force orientation, characterises the efficiency of the AUV manoeuvring. The project objectives were achieved through the extensive development of a numerical methodology to simulate, analyse, evaluate, and improve the CCPP's hydrodynamic performance. Both two-dimensional and three-dimensional periodic unsteady Reynolds-Averaged Navier-Stokes models (URANS) were developed, providing the necessary tools to numerically (re-)design the force generated by the CCPP. The developed three-dimensional methodology is shown to be suitable for the evaluation of the CCPP's current performance, analysis of further design alternatives, and even the assessment of complete new prototypes. In essence, the methodology has become a useful and powerful tool for the development of the CCPP into a viable and realisable propulsion and manoeuvring system for AUVs. Results show that the CCPP was able to generate a large, and thus, effective side-force under the various simulated operational conditions. However, for both bollard pull and captive conditions, the side-force generation is observed to be highly dependent on the generated drag force at high (collective) pitch angles. Because of the associated drag forces, the side-force generation at high pitch angles becomes highly inefficient, with large side force phase shifts occurring. The associated misorientation of the side-force cannot be compensated for efficiently by adjusting the control algorithm without affecting the overall propeller efficiency. At lower pitch angles, variation of the cyclic pitch resulted in the generation of an efficient but ineffective side-force, i.e. a (relatively) small side-force magnitude combined with a low side-force phase shift. To achieve a larger side-force magnitude at lower pitch angles, the effect of increasing the size of the propeller blades is simulated and evaluated. The applied increase in blade size has to be carefully balanced to avoid a compromised overall efficiency of the side-force generation. Through the developed numerical method, evaluation of potential shifts in operating and design conditions has been shown possible and a rationalised solution has been proposed.