Performance Analysis of a Hydrofoil with and without Leading Edge Slat

Abstract

Operational effectiveness of the wind and hydrokinetic turbines depend on the performance of the airfoils chosen. Standard airfoils historically used for wind and hydrokinetic turbines had and have the maximum lift coefficients of about 1.3 at the stall angle of attack, which is about 12o. At these conditions, the minimum flow velocities to generate electric power are about 7 m/s and 3 m/s for wind turbine and hydrokinetic turbine, respectively. Using leading edge slat, the fluid dynamics governing the flow field eliminates the separation bubble by the injection of the high momentum fluid through the slat over the main airfoil-by meaning of the flow control delays the stall up to an angle of attack of 20o, with a maximum lift coefficient of 2.2. In this study, NACA 2415 was chosen as a representative of hydrofoils while NACA 22 and NACA 97, were chosen as slat profiles, respectively. This flow has been numerically simulated by FLUENT, employing the Realizable k-e turbulence model. In the design of the wind and hydrokinetic turbines, the performance of the airfoils presented by aerodynamics CL = f (a,d), CD = f (a,d) and CL/CD = f (a,d) are the basic parameters. In this paper, optimum values of the angle of attack, slat angle and clearance space between slat and main airfoil leading to maximum lift and minimum drag, and consequently to maximum CL/CD have been numerically determined. Hence, using airfoil and hydrofoil with leading edge slat in the wind and hydrokinetic turbines, minimum wind and hydrokinetic flow velocities to produce meaningful and practical mechanical power reduces to 3-4 m /s for wind turbines and 1-1.5 m/s or less for hydrokinetic turbines. Consequently, using hydrofoil with leading edge slat may re-define the potentials of wind power and hydrokinetic power potential of the countries in the positive manner.