In order to improve the performance of small horizontal axis wind turbines at low wind speed, this study designs a novel airfoil section with an optimum transition ramp through multipoint inverse design method. A viscous analysis code is used to close the design loop. Further, Shear stress transport-transition model in ANSYS-Fluent is employed with modified constants to analyze the flow and aerodynamic performance of the airfoil at Reynolds numbers 60 000, 100 000, 200 000, 300 000 and 500 000. Next we consider the designing of a 2m rotor from the new airfoil section using an evolutionary algorithm for optimization. The power coefficient and self starting of a small 2m wind turbine is improved significantly with the chosen generator resistive torque of 0.5Nm, the new airfoil section and the optimization technique for finding the optimal values of the parameters.
The mechanism of the laminar separation bubble and the laminar-turbulent transition over the airfoil UBD5494 is simulated in ANSYS-FLUENT using the transition gamma À Re h model at Reynolds number 6 9 10 4 , 1 9 10 5 , 1.5 9 10 5 , 2 9 10 5 and 3 9 10 5 . Modified constants of the Reynolds momentum thickness are incorporated in the model. The aerodynamic performance of the airfoil is also examined against the flow behaviour. Simulation results show that with the increase in angle of attack, laminar separation bubble moves towards the leading edge and at the same time contracts in size. It starts to expand after reaching the foremost point of the leading edge and then bursts, resulting in flow turbulence and stall. With decreasing Re, the size of the laminar separation bubble is found to be increasing and its progress towards the leading edge is noticed to be slower. The numerical results also indicated that UBD5494 airfoil has enhanced lift-to-drag ratio and desirable stall characteristics which are distinctively advantageous for the better performance of small wind turbine rotors.
This paper presents a set of fluid flow patterns obtained by oil flow visualization method over a low Reynolds number airfoil at angle of attack = 4°, 8°, 12° and 15°. The experiments were conducted in a low speed wind tunnel at Reynolds number = 60,000 and 100,000. The aerodynamic performance of the airfoil is also shown for direct comparison with the flow features. The experimental results showed that with increase in both the Reynolds number and the angle of attack, the extent of the laminar separation bubble diminish and at the same time progress towards the leading edge. At angle of attack ≈ 12° shorter bubble at the leading edge was found to burst and reform into a rather longer bubble causing major increase in drag values.
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