Date of Award

May 2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Ryoichi S Amano

Committee Members

Yongjin Sung, Lei Wang, Ilya Avdeev, Habibollah Tabatabai

Keywords

Aerodynamics, CFD, HAWT, J-shaped Airfoils, Wind Energy, Winglet

Abstract

Wind energy as a promising energy solution has drawn the attention of many researchers to enhance its generation efficiency. Understanding the aerodynamics of the new designs and configurations of airfoils is crucial in predicting the aerodynamic behavior of wind turbine rotors. Improving the aerodynamic performance of airfoils participates to a far extent in improving a turbine's performance, hence increasing a turbine's power output. Studying aerodynamic performance for both airfoils and wind turbines can be done either by wind tunnel testing, Computational Fluid Dynamics (CFD) techniques, or both. In the first chapter, an introduction was provided for wind energy, two-dimensional airfoils, and wind energy converters. In the second chapter, the effect of the inner opening ratio on the J-shaped airfoils aerodynamic performance was studied and documented for symmetrical airfoils. Three different airfoil thicknesses were investigated: small (NACA0008), medium (NACA0015), and large (NACA0024). The effects of three inner opening ratios were analyzed for each airfoil thickness: one-third, one-half, and two-thirds. The performance of each opening ratio was compared with the performance of the solid airfoil “zero opening ratio” for different angles of attack between 5o and 20o. All designs were simulated using the CFD technology after validating CFD simulation results against experimental results for solid NACA4412 airfoil in the University of Wisconsin Milwaukee (UWM) wind tunnel facility and other published experimental data. It was found that the unsteady Large Eddy Simulation method yields accurate solutions with fewer mesh cells compared with the steady k-ω turbulence model, but with much longer computational time. The lift-to-drag ratio for all studied airfoils has a maximum value for solid airfoils compared to those equipped with openings. For airfoils equipped with a 00.00% opening ratio ‘solid,’ NACA0015 airfoil has the maximum lift-to-drag ratio. Furthermore, it was found that NACA0008 equipped with a 33.33% opening ratio performs better than all studied J-shaped airfoils. In the third chapter, the effect of winglet direction and cant angle on the power production of a small-scale Horizontal Axis Wind Turbine (HAWT) was investigated numerically using CFD techniques after measuring the experimental Tip Speed Ratio (TSR) experimentally in the UWM Wind Tunnel Facility. Suction side and pressure side winglets were studied over a wide range of cant angles between -90 degrees and +90 degrees using three wind speeds 5, 10, and 15 m/s. Blade Element Momentum (BEM) theory was used to design the optimum twisted blade as a baseline design. The output power was the key parameter in this part of the study, where each design power output was compared to the baseline design without winglets. All winglet design parameters other than the cant angle (length, radius of curvature, and toe, twist, and sweep angles) were fixed throughout this study to isolate their effect. CFD methods were used to capture the aerodynamic performance for the most promising configuration. It was found that all the upstream and downstream wingletted turbines outperformed the baseline design except for the perpendicular downstream (-90o) winglet at low wind speed. Furthermore, it was found that the enhancement is more pronounced with higher velocities. In the fourth chapter, the performance of new two-dimensional airfoil designs was simulated and compared with the performance of a baseline design. The studied designs were J-shaped and Kammtail Virtual Foil (KVF) profiles. Three J-shaped pressure side truncation ratios (1/3, 1/2, and 2/3) and two KVF truncation ratios (1/8 and 1/4) were studied. All proposed designs were first investigated in a two-dimensional simulation study to get the lift-to-drag ratio by applying two wind speeds (5 m/s and 10 m/s) and varying the angle of attack (AoA). AoA was varied between 0o and 20o by a step of 5o. Lift and drag forces were calculated and used to calculate the lift-to-drag ratios for each case. It was found that the J-shaped designs enhanced the lift-to-drag ratio with higher AoAs for 5 m/s wind speed. Furthermore, the J-shaped airfoils experienced an increased lift at all studied AoAs. On the other hand, KVF designs enhanced the lift-to-drag ratio, especially with higher AoAs. However, the enhancement was not because of an increased lift but rather because of a reduced planner area and reduced drag. The performance of the new J-shaped and KVF airfoil designs for small-scale horizontal axis wind turbines (HAWTs) was studied and compared with the performance of a baseline design. The baseline design was experimentally investigated. Output power was measured using a digital rotary torque sensor using three different wind speeds (8 m/s, 10 m/s, and 12 m/s). Tip speed ratio (TSR) was calculated after measuring each wind speed's free rotating revolutions per minute (RPM). Three wind speeds and experimental TSRs were used in three-dimensional simulations to capture the performances of the proposed designs and compare them with the baseline. The baseline design subjected to 8 m/s air flow was used to carry out a mesh independence study and to validate the used CFD formulation. Simulated power percent error was around 9% over the entire wind speeds range. Hot Wire Anemometer (HWA) was used to map the experimental wind speed in the direction of flow at one diameter downstream. Experimental wind speed was compared with the simulation wind speed at one diameter downstream and the comparison showed a good agreement. The simulation investigation was carried out for lab-scale and scaled designs. It was found that the J-shaped blades enhanced the performance of the HAWTs for both lab-scale and scaled designs. J-shaped blades with a 1/3 opening ratio yielded an average power coefficient enhancement of around 1.56% and 4.16% for lab-scale and scaled designs, respectively. J-shaped blades with a 1/2 opening ratio yielded an average power coefficient enhancement of around 1.15% and 4.23% for lab-scale and scaled designs, respectively. On the other hand, J-shaped blades with a 2/3 opening ratio yielded an average power coefficient enhancement of around -0.12% and 2.54% for lab-scale and scaled designs, respectively. Furthermore, it was found that the KVF blades diminished the performance for both lab-scale and scaled designs. The synergy of combining two blade design modifications (namely winglet and J-shaped truncations) was studied for scaled designs. J(1/3) truncation was combined with ±30^o and ±90^o cant angle winglets. It was found that the combination enhanced the averaged power coefficient over studied wind speeds. Furthermore, it was found that the combination has a synergetic effect on the power coefficient.

Download

Available for download on Saturday, June 06, 2026

Share

COinS