Ducted rotors are configurations known to outperform their unducted reference baselines when aerodynamic performance is concerned. Aside from aerodynamic benefits in hover, a duct also affects acoustic emissions. One of the most contended design parameters of a duct-rotor assembly is the radial distance between the blade tip and the duct wall, referred to as the “tip gap”. The present study explains how the aerodynamic performance of a ducted-rotor system is affected by the tip-gap distance, taking into account the performance of the rotor and those of the duct's inlet lip and diffuser sections. Separate thrust measurements of the rotor and duct establish that the latter can generate up to half of the total thrust of the assembly. Static wall-pressure measurements along the inner wall of the duct reveal a low pressure suction zone over the duct's inlet lip area. This allows the assembly to generate more thrust than the rotor alone, even though the duct's diffuser section generates a drag component (negative thrust). From the velocity fields it is further shown that the performance-deterioration with an increasing tip gap distance is associated with a contraction of the rotor slipstream in the duct diffuser. ... Read more

It is expected that several identical Point Absorber Wave Energy Converters (PAWECs) will be arranged in arrays to form a Wave Energy Farm. One of the key challenges in designing such a WEC array is their spatial configuration, as the WECs in the farm interact hydrodynamically with each other. This study focuses on different potential PAWEC deployments to identify the best relative position in order to maximise energy output. This is done by resolving the hydrodynamic interactions between a modelled WEC point absorber, with use of open-source Boundary Element Methods (BEM) and time domain WEC simulator. The results from the numerical model are also compared with wave tank testing, to verify
the accuracy of the analysis. The simulations show that the relative position can significantly increase a WEC’s individual power output. A spatial pattern of relative positions that result in higher potential power extraction was shown, with increases up to 20% compared to a single WEC on its own. However, the computational results showed realistic results for only a select number of configurations. As for the experiment, unexpected variations in test conditions occurred, inhibiting the possibility to isolate certain events. Therefore, when cross checking results from both simulations and experiments, the identified simulated trends only partially showed adherence with the experimental data. Henceforth, the knowledge gathered from the simulations can’t conclusively be validated by the experiments conducted in this study. This study shows that the spatial configuration of two WECs influences their individual power outputs. ... Read more