Ivaylo Nedyalkov

Optical coherence tomography-based micro-particle image velocimetry.

We present a new application of optical coherence tomography (OCT), widely used in biomedical imaging, to flow analysis in near-wall hydrodynamics for marine research. This unique capability, called OCT micro-particle image velocimetry, provides a high-resolution view of microscopic flow phenomena and measurement of flow statistics within the first millimeter of a boundary layer. The technique is demonstrated in a small flow cuvette and in a water tunnel.

Cavitation Investigation of Hydrofoils for Marine Hydrokinetic Turbines

Three different hydrofoil sections were investigated in the recently renovated High-Speed Cavitation Tunnel (HiCaT) at the University of New Hampshire: a NACA 0015 (reference foil), a NACA 63-424, and a bidirectional version of the NACA 63-424 hydrofoil. Bi-directional hydrofoils are of interest for marine renewable energy conversion, since they allow the elimination of pitch control mechanisms on marine hydrokinetic turbines. Hydrofoil lift and drag were measured for different velocities, pressures, and angles of attack. For some experimental conditions, comparative PIV measurements were performed in the near-wake region. A cavitation inception model for marine hydrokinetic turbines was derived. Cavitation numbers for inception were obtained for the two NACA 63-424 foils by varying pressure at constant speed as well as by varying speed at constant pressure. The performance of the NACA 63-424 and the bidirectional NACA 63-424 was compared.Copyright

Performance of Bi-Directional Blades for Tidal Current Turbines

Horizontal-Axis Tidal Current Turbines can utilize bi-directional blades which operate well in both directions in a reversing flow, avoiding the use of yaw or pitch mechanisms, thus reducing initial and maintenance costs. A “class” of bi-directional hydrofoil shapes was designed, and studied numerically using OpenFOAM, and one foil with favorable characteristics, named B3-351045, was tested experimentally in the University of New Hampshire High-Speed Cavitation Tunnel - HiCaT. The foils were designed with considerations for lift, drag, and cavitation inception. Simplified 2D simulations for a range of angles of attack for foils with different foil-geometry parameters were used to select a favorable hydrofoil. The selected hydrofoil was fabricated and tested in the HiCaT. Lift and drag were measured using a custom-designed force balance and cavitation inception was observed visually. Experimental and numerical data were compared. Bi-directional blades may be an economically-feasible option when addressing the reversing direction of tidal flows, since the decreased performance of the blades can be offset by the lower costs compared to unidirectional blades.Copyright