Wind Turbine Wakes and Interference R Ganesh Rajagopalan

Wind Turbine Wakes and Interference R. Ganesh Rajagopalan Department of Aerospace Eng. Iowa State University

Research Needs in Wind Energy • Wind Turbines are Complex Aerodynamic Machines. • The wind turbine wakes are unsteady and interact strongly with each other. • The nature and shape of the terrain has significant impact on the performance of the turbines. • Need designs that survive 20 year fatigue loads • Turbines need to be stronger, smarter and less expensive

Research Paradigm • Obtaining an engineering solution to the complex physics that dictates these multidimensional class of problems. • Need to produce solutions cost effectively, in a timely manner. • Modularize the problem to allow parallel development.

Research Problem • Turbines are designed as individual turbines. • In an aerodynamically interacting environment their behavior and performance are not well understood. • Interactions must be simulated with a goal to understand the basic physics and optimize performance.

Components of the Problem • The Resource: Turbulent Wind • The Turbine: Complex Rotating Blades with multiple degrees of freedom • The environment: Complex terrain • The Interaction: Unsteady wakes from different turbines.

The Resource • Assume that the flow is unsteady and that the direction and magnitude are stochastic.

The Terrain • Allow for body conforming grids to account for topography changes (large and small)

The Rotating Blades • An Engineering to Model to allow simulation of many turbines operating in the vicinity.

Basic Validation • Integrated Performance (Power Coefficient). • Forces and Moments as the blades rotate. • Wakes

Multiple Turbine Interactions

NREL Combined Experiment : Two HAWTs relative to each other • Considering only two NREL upwind rotors, without tower and nacelle • Relative distance : Diameter 4* • Angle sweep: [0 to 90 deg] • Rot 3 dc solutions presented Iowa State University 30

NREL Combined Experiment : Two HAWTs relative to each other Cases Tested Iowa State University 31

NREL Combined Experiment : Two HAWTs (Vo = 10 m/s) Power Ratio vs. Angle between HAWTs (Psa = Power of a standalone HAWT under same conditions = 17. 818 k. W) 32 Iowa State University

NREL Combined Experiment : Two HAWTs (Vo = 10 m/s) Case B Y = 150 Case A Y = 00 Velocity magnitude in the wake 33 Iowa State University

NREL Combined Experiment : Two HAWTs (Vo = 10 m/s) Case B Y = 150 Case A Y = 00 Axial induced velocity on the rotor plane 34 Iowa State University

NREL Combined Experiment : Two HAWTs (Vo = 10 m/s) Case E Y = 600 Case C Y = 300 Axial induced velocity on the rotor plane 35 Iowa State University

Conclusions • Rot 3 dc : - accurate modeling of flows through HAWTs and VAWTS, including yaw effect - validated against field test data • Interference studies : - demonstration of Rot 3 dc as an effective tool for qualitative and quantitative study of multiple turbine configurations - Further studies with parametric variations of relative distance and with an array of HAWTs required 37 Iowa State University

Future Research • Improve the cost of computation by smarter numerical algorithms. • Use modern hardware such as GPU to do parallel computation to decrease the simulation time. • Improve the physical representation of the turbines by allowing yaw based on wind conditions.