WIND TUNNEL ANALYSIS OF A COUNTER-ROTATING WIND TURBINE

Wind power is a reliable form of energy, and increases in wind turbine efficiency have helped to provide cost-effective power to an ever-growing portion of the world. However, there are physical limits to the amount of energy that can be removed from an airstream using a single wind turbine system. This paper explores the possibility of increasing power production using two counter-rotating sets of wind turbine blades. A review of design characteristics, such as number of blades, blade angle of twist, chord length, and generator efficiencies, resulted in the design of a counter-rotating wind turbine using three different National Renewable Energy Laboratory (NREL) cross-sectional blade profiles for the blades. A three-blade front system and two three-blade rear systems were studied. The blade prototypes were modeled in SolidWorks ® , produced using a Dimension ® 3D printer, and then tested using two Parallax™ four-pole stepper motors as generators in a model 406B ELD wind tunnel. Initial testing showed a power increase of 101.4% at 25 mph. This power increase can be attributed to the addition of the second generator and a rear-blade system that was a mirror image of the front system. Testing was performed between 15 mph and 40 mph in 5-mph increments. The counter-rotating system reached its optimum operating efficiency at 25 mph, at which 12.6% of the energy in the air was converted into usable power. This outcome compares to a 6.25% power conversion for the frontblade system. Preliminary results indicate that a counter-rotating assembly is promising for increasing energy extraction from a column of air. Additional testing should focus on system efficiency based on blade angle of twist, chord length, and generator efficiencies. A power increase of 101.4% with the addition of the rear-blade system indicates that the front-system efficiency has not been maximized. The next logical step is designing blade systems for maximum total system efficiency at specified wind speeds. Additionally, it would be valuable to determine if counter-rotating systems could expand the range of possible turbine locations by lowering the required average wind speed.