This research thesis focuses on conducting experimental research into the hydrodynamic properties of a NACA 0012 T-foil in dynamic conditions. An aerodynamically smooth surface was created and used for all dynamic experiments. For exploratory research into the effect of surface finish on the performance of a T-foil in steady state conditions, a second, unfinished but structurally equal, T-foil was made using .15 mm 3D printing layers aligned with the flow.
The hydrodynamic properties were determined by conducting experiments in steady state conditions using conventional towing tank methods. Combining all steady state experiments, the lift and drag coefficient on the foil are expressed as a function of angle of attack, freestream velocity and submergence for a Reynolds number of 1.5·105. The surface finish of the second, raw printed, T-foil resulted in a lower critical Reynolds number of 3.3 · 105 compared to 4.5 · 105 for the aerodynamically smooth foil.
Dynamic flow conditions were simulated in experiments where the setup was subjected to either: sinusoidal pitch motion, sinusoidal heaving motion or waves. As a result of the imposed motions, the static forces on the setup change and inertial forces occur. To compensate for this, a function was made from all static measurements. The inertial forces are compensated by applying a mass/inertia matrix.
Using this new method of towing tank research, the steady state behaviour of a T-foil is described using dynamic experiments. The novel method to determine steady state characteristics includes two angle sweeps, one positive and one negative. The rate of change proves to be sufficiently slow at 0.8 ◦ s−1 for v∞ = 2 ms−1, producing more accurate results while towing tank time can be reduced by 78%.
From the steady state results a model is created. Because this model is limited to Re = 1.5 · 105, it is enriched with a prediction model based on X-foil which is compensated for induced drag, finite foil shape and free surface effects.
The prediction shows good correlation with the results in z-direction for both imposed sinusoidal heaving and pitching motions. During sinusoidal heaving, flow remains attached longer leading to higher and more stable lift and drag at higher absolute angles. In pitching a similar effect can be seen leading to increased fluctuations and slightly higher average lift compared to the prediction models. For both imposed motions, lower drag is measured with respect to both the predictions and the measurement in steady state conditions. An additional component to the drag occurs during a sinusoidal pitching motion. This additional component has a sinusoidal behaviour equal to the imposed motion which suggests that it is caused by induced drag.
When the freestream velocity was increased from 2 to 6 ms−1 in similar waves, it was found that the sinusoidal response of the hydrodynamic forces shifted by ± π rad. Similar to the imposed dynamic motions, predictions show larger values for drag. It was found that the wave height can be related to the drag. When wave height is increased, the drag is reduced.