Abstract
Dynamic stall control of a S809 airfoil is numerically investigated by implementing a co-flow jet (CFJ). The numerical methods of the solver are validated by comparing results with the baseline experiment as well as a NACA 6415-based CFJ experiment, showing good agreement in both static and dynamic characteristics. The CFJ airfoil with inactive jet is simulated to study the impact that the jet channel imposes upon the dynamic characteristics. It is shown that the presence of a long jet channel could cause a negative effect of decreasing lift and increasing drag, leading to fluctuating extreme loads in terms of drag and moment. The main focus of the present research is the investigation of the dynamic characteristics of the CFJ airfoil with three different jet momentum coefficients, which are compared with the baseline, giving encouraging results. Dynamic stall can be greatly suppressed, showing a very good control performance of significantly increased lift and reduced drag and moment. Analysis of the amplitude of variation in the aerodynamic coefficients indicates that the fluctuating extreme aerodynamic loads are significantly alleviated, which is conducive to structural reliability and improved life cycle. The energy consumption analysis shows that the CFJ concept is applicable and economical in controlling dynamic stall.
Highlights
In the Half Year Report of World Wind Energy Association [2], it was reported that the growth of the wind energy industry will continue with the rapid increase in energy demand, more efforts are still needed to increase the efficiency of wind energy generation in order to keep wind energy economically competitive compared with traditional fossil fuels and other renewable energy sources such as hydroelectric energy, solar energy and bio-energy
The present study investigates the unsteady aerodynamic characteristics of the NREL S809 baseline and co-flow jet (CFJ) airfoils undergoing sinusoidal pitch oscillations about the quarter chord point with various jet momentum coefficients
The static prediction precision of the solver has been validated in a previous study [21] by comparing the numerical results of NREL S809 airfoil static characteristics with the experiment conducted in the Delft University of Technology [34]
Summary
The depletion of fossil-fuel reserves, stricter environmental regulations and the world’s ever-growing energy demand have greatly promoted the usage of alternative renewable energy sources. Since the beginning of the commercial wind industry, the rotor diameter and turbine size have gradually increased in order to capture more energy during the lifetime. As turbines grow in size, the structural and fatigue loads become more noticeable. The extreme structural and fatigue loads are important factors in turbine design and most of these loads result from the dynamic stall. A dynamic stall phenomenon takes place when the wind turbine blade section is subjected to unsteady variation of angle of attack. Due to the complicated atmospheric environment at wind farms, wind turbine blades usually experience adverse conditions under which the local angle of attack of a particular blade
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