Date of Award
Program or Major
Doctor of Philosophy
Hydrofoils have a wide range of applications - from hydro-power generation to marine propulsion. Bi-directional hydrofoils have (comparatively) identical performance when operating in both directions of reversing flows. A typical application of such foils is tidal current power generation; where by using bi-directional blades the need for aligning the rotor (yaw) or blades (pitch) of the turbines to account for the changing flow direction is eliminated. This leads to lower initial, and more importantly, maintenance costs.
A numerical test-bed was developed for studying bi-directional hydrofoils, and foils in general. The test-bed generates all necessary files for flow simulations in OpenFOAM, an open-source Computational Fluid Dynamics (CFD) framework. These include files for geometry, mesh, boundary conditions, simulation parameters, and codes for automatic post-processing of the data. In the interest of shorter simulation times for studying a wide range of foils, the turbulence model used in the present study was k-omega SST. However, the test-bed can be set up to utilize (almost) any feature of OpenFOAM, including a variety of turbulence models.
Mesh convergence studies were performed for three reference foils (NACA 0015, NACA 63-424, and a bi-directional version of the NACA 63-424 - NACA 63-424B); then 3D numerical data for the foils were compared to experimental results obtained for the same flow configurations. Eleven classes of bi-directional foils were developed and by varying geometric parameters, approximately 700 new foils were designed and studied numerically. Based on the simulations of these foils, which provided estimates for the lift and drag coefficients and the inception cavitation numbers, two classes of foils were selected for further investigation. Then, two novel foils from these classes were studied further using a simulated water tunnel, and the results were compared to experimental data.
Experiments were performed in a high-speed water tunnel to measure the lift, drag, and inception cavitation numbers of physical models of the three reference foils, the two novel foils, and the two novel foils manufactured with defective leading/trailing edges. Detailed error estimation analysis was performed to evaluate the accuracy of the experimental setup and data.
A cavitation inception model was developed to predict cavitation inception for horizontal axis tidal current turbines for different operating conditions, and thus assist with their design. Two cases of how the model can be implemented were presented. The model is also an example of how numerical and experimental data obtained in this study can be utilized.
Some of the studied bi-directional blades (foils) have similar performance and cavitation characteristics to conventional blades. Small decreases in performance may be offset by the decreased initial and maintenance costs. Numerical and experimental test-beds for bi-directional foils were established and will significantly simplify further development of this type of hydrofoils. Additional structural, economic feasibility, and fluids-structure interaction studies will be required before new bi-directional hydrofoils can be used in practical applications.
Supplemental files of the numerical test-bed are provided.
Nedyalkov, Ivaylo Petrov, "PERFORMANCE AND CAVITATION CHARACTERISTICS OF BI-DIRECTIONAL HYDROFOILS" (2014). Doctoral Dissertations. 2169.