Abstract
The feasibility of using crossflow runners as single rotors in vertical-axis wind turbines (VAWT) or as blades in horizontal-axis wind turbines (HAWT) is numerically studied. A computational fluid dynamics model is validated from data obtained in a wind tunnel. Three crossflow runners with different number of blades are tested. Values of drag, lift and torque coefficients are numerically obtained at different turning velocities. Power coefficients Cp for crossflow VAWT and HAWT are calculated for different tip-speed ratios (TSR) and runner spin ratios (α). Since crossflow HAWT consume electrical energy for spinning the runners, the net power coefficient is estimated. Simulations indicate that a crossflow runner as a single rotor in VAWT should have a high solidity and work at low TSR. Crossflow runners working as blades in HAWT may achieve low drag to lift ratios but the Cp is penalized by the amount of energy required for spinning the runners. The optimum working condition of crossflow HAWT is located within a narrow band of low TSR and α reaching Cp values < 0.2 only.
Highlights
Wind energy technologies have experienced an important evolution over the last decades [1].In large scale designs, the horizontal-axis wind turbine (HAWT) with a three-blade rotor offers a high aerodynamic performance, being the most suitable option for wind farms with large installed capacities [2,3]
Crossflow runners working as blades in horizontal-axis wind turbines (HAWT) may achieve low drag to lift ratios but the Cp is penalized by the amount of energy required for spinning the runners
The horizontal-axis wind turbine (HAWT) with a three-blade rotor offers a high aerodynamic performance, being the most suitable option for wind farms with large installed capacities [2,3]. This type of HAWT commonly starts working at wind speeds over U = 3.5 m s−1 and with tip-speed ratios (TSR) in the range of 10–13 [2], where TSR is the ratio of the blade tip tangential velocity Ut to the wind speed U, ΩR
Summary
Wind energy technologies have experienced an important evolution over the last decades [1]. Sedaghat [15] has recently developed a theory for designing Magnus wind turbines with rotating cylinders working as blades in HAWT, estimating an optimum of Cp = 0.35 at TSR = 1 in the range of 1.5 < α < 2.5 (see Table 1). External energy (not related with the incoming air flow) is required for spinning the runner at fixed angular velocities in other regimes (e.g., 0 < α) This is a proper functioning for crossflow runners that work as blades in HAWT (as in Magnus HAWT [15]; see Table 2 and Figure 1). Achieved by and achieved by the effect of the air flow); and (b) as blades in horizontal-axis wind turbines (HAWT)(ω(ω (ω must be externally externallysupplied supplied by, for example, electrical motors).
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