Aerodynamic Loads and Performance of the Darrieus Rotor

The double-multiple-streamtube model was used for determining the aerodynamic blade loads and roto performance on the Darrieus vertical-axis wind turbine with curved blades. This analytical model i capable of predicting the difference in the induced velocities at the upstream and downstream passes. The upwind and downwind interference factors are calculated by a double iteration, one for each half of the rotor and vertical variations in the freestream velocity are accounted for. Under local aerodynamic conditions a closed-form analytical solution is obtained for two functions, one for the upwind and one for the downwind hal of the turbine. Thus the local aerodynamic loads on the blade and the rotor performance are calculated more accurately than by other streamtube methods. Comparison of the analytical results obtained with the doublemultiple-streamtube model and the available field test data for the Sandia 17-m machine shows good agreement. This method can therefore be used for generating a suitable aerodynamic-load model for structural-design analysis of the Darrieus rotor.