Browsing by Author "Balas, C."

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    Numerical and Experimental Analysis of the Twin-Blade Hydrofoil for Hydro and Wind Turbine Applications
    (2015) Koc, E.; Yavuz, T.; Kilkis, B.; Erol, O.; Balas, C.; Aydemir, M. T.; 0000-0003-2580-3910; ABE-2872-2020; AAJ-2321-2020
    In this study, the hydrodynamic performance of a twin-blade hydrofoil has been numerically and experimentally investigated in three dimensions for tip speed ratios ranging between 1.5 and 5.5. The optimum geometric and flow parameters leading to the maximum value of the C-L/C-D ratio, which is the major design parameter of the wind and hydrokinetic turbines, have been determined. At a design flow velocity of 2 m/s (Re=3 x 10(5)) the maximum power coefficient of 0.457 was obtained at the tip velocity ratio of 3.5 at optimum geometric parameters of h/c(1) =0.667, c(1)/c(2)= 0.671 and the angle of attack of 3 degrees. The maximum torque of 224 Nm was obtained at the tip speed ratio of 2.5 for a prototype that has been built and tested during the experimental studies. The experimental studies were conducted in a towing tank, by which a power coefficient of 0.424 at the tip speed ratio of 3.48 was obtained. This speed ratio of 3.48 is about 7% lower than the numerical results. The optimum tip speed ratio of 3.5 is quite low when compared with the optimum tip speed ratio of 5.0 for the three bladed standard wind turbines. The advantage of employing twin-blade hydrofoils or airfoil is the potential of achieving better engineering designs and applications of wind and hydrokinetic turbines, which can be used for power generation purposes starting-up at lower wind and hydraulic current velocities. (C) 2015 Elsevier Ltd. All rights reserved.
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    Performance Analysis of the Airfoil-Slat Arrangements for Hydro and Wind Turbine Applications
    (2015) Yavuz, T.; Koc, E.; Kilkis, B.; Erol, O.; Balas, C.; Aydemir, T.; 0000-0003-2580-3910; ABE-2872-2020; AAJ-2321-2020
    Standard airfoils historically used for wind and hydrokinetic turbines had maximum lift coefficients of around 1.3 at stall angles of attack, which is about 12 degrees. At these conditions, the minimum flow velocities to generate electric power were about 7 m/s and 2 m/s for the wind turbine and the hydrokinetic turbine cases, respectively. In this study, NACA4412-NACA6411 slat-airfoil arrangement was chosen for these two cases in order to investigate the potential performance improvements. Aerodynamic performances of these cases were both numerically and experimentally investigated. The 2D and 3D numerical analysis software were used and the optimum geometric and flow conditions leading to the maximum power coefficient or the maximum lift to drag ratio were obtained. The maximum lift to drag ratio of 24.16 was obtained at the optimum geometric and flow parameters. The maximum power coefficient of 0.506 and the maximum torque were determined at the tip speed ratios of 5.5 and 4.0 respectively. The experimental work conducted in a towing tank gave the power coefficient to be 0.47 which is about %7 lower than the numerical results obtained. Hence, there is reasonable agreement between numerical end experimental values. It may be concluded that slat-hydrofoil or airfoil arrangements may be applied in the design of wind and hydrokinetic turbines for electrical power generation in lower wind velocities (3 -4 m/s) and current velocities (about I m/s). (C) 2014 Elsevier Ltd. All rights reserved.