Wind Turbine Wakes and Interference

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

2. 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

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

4. 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.

5. 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.

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

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

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

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

29. Multiple Turbine Interactions

30. NREL Combined Experiment :Two HAWTs relative to each other • Considering only two NREL upwind rotors, without tower and nacelle • Relative distance : 4 * Diameter • Angle sweep: [0 to 90 deg] • Rot3dc solutions presented Iowa State University

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

32. 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 kW) Iowa State University

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

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

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

37. Conclusions • Rot3dc : - accurate modeling of flows through HAWTs and VAWTS, including yaw effect • - validated against field test data • Interference studies : • - demonstration of Rot3dc 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 Iowa State University

38. 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.