Although wind turbines are widely used for conversion of wind energy to electrical power, there are still many opportunities for improvements in their design and operation to increase the efficiency of wind energy harvesting, and the reduction in cost that results from these improvements. A key area for improvement is the design of the turbine rotor blade. Structural, manufacturing, and transportation constraints in utility-scale wind turbines lead to aerodynamically imperfect blade designs, especially in the root region near the hub joining the rotor blade. Root loss is estimated to cause about 5% loss in wind energy extraction for a single wind turbine. This problem is compounded in wind farms containing many wind turbines, where mixing of air creates a wake. Wake losses in wind farms resulting from the ingestion of upstream turbine wakes by downstream turbines range between 8 to 40% of wind energy harvesting efficiency, depending on onshore vs. off shore wind farm location, turbine layout, and atmospheric stability conditions. The goal of this research is to conduct a comprehensive theoretical and experimental study to explore a novel dual-rotor wind turbine (DRWT) concept to mitigate these losses for improved turbine performance and wind farm efficiency. In this dual-rotor concept, a smaller set of turbine blades is positioned near the larger blades to reduce the root loss and improve wind turbine efficiency using aerodynamic principles. This novel dual-rotor wind turbine configuration will be studied experimentally using scale models in a wind tunnel. Experimental studies will be complimented by advanced computer simulations to identify the best design for the dual rotor system. With respect to education and broadening participation, course modules developed from these research efforts will be incorporated into the undergraduate and graduate mechanical and aerospace engineering courses at Iowa State University (ISU). Existing programs at ISU will be used to recruit students from under-represented groups in engineering for participation in the research project. The project results will also be used to prepare seminars and demonstrations on Renewable Energy and Wind Turbine Technology for presentation at local K-12 schools to increase public awareness about recent advances in wind energy. The project will also continue existing collaborations with wind turbine manufacturers.
Structural, manufacturing, and transportation constraints in utility-scale wind turbines lead to aerodynamically imperfect blade designs, especially in the root region near the hub joining the rotor blade. Root loss is estimated to cause about 5% loss in wind energy extraction for a single wind turbine. The goal of this research is to conduct a comprehensive theoretical, numerical, and experimental study to explore a novel dual-rotor wind turbine (DRWT) concept to mitigate root losses for improved turbine performance and wind farm efficiency. The proposed DRWT concept will employ a secondary, smaller, co-axial rotor that is intended to mitigate losses incurred in the root region of the main rotor by using an aerodynamically optimized secondary rotor, and also mitigate wake losses in wind farms through rapid mixing of turbine wake and increased upper-layer flow entrainment. The integration of experimental and numerical modeling studies will enable a first-principles based evaluation of the proposed DRWT concept. Numerical simulations will first be used to design an aerodynamically optimum DRWT. Aerodynamic performance of the optimized DRWT will be investigated for operation of a single turbine and then a turbine array sited in non-homogenous atmospheric boundary layer (ABL) flows. Towards this end, the large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) wind tunnel at Iowa State University (ISU) will be used for the experimental study. In addition to measuring turbine power outputs and dynamic wind loads acting on model DRWTs, a high-resolution Particle Image Velocimetry (PIV) system will measure the flow field to characterize turbine wake-vortex system dynamics relative to conventional single-rotor wind turbines. Highly resolved Large Eddy Simulations (LES) will be also performed in coordination with the experimental study to elucidate the underlying flow physics. With respect to broader impacts in education and outreach, the project results will also be used to prepare seminars and demonstrations on Renewable Energy and Wind Turbine Technology for presentation at local K-12 schools to increase public awareness about recent advances in wind energy. The project will also continue existing collaborations with wind turbine manufacturers.
