Wind Turbine Wakes and Interference

R. Ganesh RajagopalanDepartment 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 multi-dimensional 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

30Iowa State University

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

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NREL Combined Experiment :Two HAWTs relative to each other

Cases Tested

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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)

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Case A Y = 00

NREL Combined Experiment :Two HAWTs (Vo = 10 m/s)

Velocity magnitude in the wake

Case B Y = 150

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NREL Combined Experiment :Two HAWTs (Vo = 10 m/s)

Axial induced velocity on the rotor plane

Case A Y = 00

Case B Y = 150

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NREL Combined Experiment :Two HAWTs (Vo = 10 m/s)

Axial induced velocity on the rotor plane

Case C Y = 300

Case E Y = 600

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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

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.