1. Introduction 20 kW Demonstration Key Accomplishments
Plasma Flow Control for Wind Turbines
Neal E. Fine, PhD
July 2015
Neal E. Fine, PhD 07/06/15 1/10
2. Introduction 20 kW Demonstration Key Accomplishments
Introduction to Plasma Flow Control
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Surface mounted plasma actuator:
• High sectional lift, low drag
• Solid state, no moving parts
• Leads to improved aerodynamic efficiency
• Can be used to increase wind turbine AEP
3. Introduction 20 kW Demonstration Key Accomplishments
Introduction to Plasma Flow Control
Neal E. Fine, PhD 07/06/15 3/10
Advanced proprietary plasma actuator
• Proven technology
• High control authority
• Conformal to blade
• Low power
• High reliability
• Fast reacting and adaptive
• Controllable
Exposed Electrode
Insulated Electrode
Dielectric Plasma
AC
Voltage
Induced Flow
Exposed Electrode
Insulated Electrode
Dielectric Plasma
AC
Voltage
Induced Flow
Plasma Actuator
4. Introduction 20 kW Demonstration Key Accomplishments
Benefits
• Improved aerodynamic performance,
leading to increased energy capture
— Increased sectional lift leads to increased CP
— Increased CP in Region 2 of 5-15% or higher
— Increased AEP of 5-10%, or higher
• Reduced reliance on pitch for pitch-
controlled turbines
• Reduction in fatigue loads in Region 3
Neal E. Fine, PhD 07/06/15 4/10
Results
0
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-10 -5 0 5 10 15
LiftCoefficient
Angle of Attack (deg)
Lift Coefficient vs Angle of Attack (deg)
Plasma On
Plasma Off
35%
INCREASE
5. Introduction 20 kW Demonstration Key Accomplishments
Leveraging $3M in Government R&D
• ONR-sponsored demonstration project, 2012-2015
• Demonstrated on a Renewegy VP20 turbine mounted
on the wing walls of Navatek’s dry dock in Honolulu
• Supported by wind tunnel testing and performance
predictions
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6. Introduction 20 kW Demonstration Key Accomplishments
VP20 Demonstration
Shore-side turbine is outfitted
with the demonstration system.
Renewegy VP20
• 9.5 m diameter
• 20 kW nameplate rating
• Variable speed
• Pitch controlled
• Rated wind speed 14.5 m/s
Hydraulic lift kit
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7. Introduction 20 kW Demonstration Key Accomplishments
System Architecture
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slip ring
anti-rotation
bracket
3x transformer
inductor
hub bracket
8. Introduction 20 kW Demonstration Key Accomplishments
System Architecture
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9. Introduction 20 kW Demonstration Key Accomplishments
System Architecture
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10. Introduction 20 kW Demonstration Key Accomplishments
Key Accomplishments
Facilities
• State-of-the-art plasma lab with custom-built low-speed wind tunnel
Actuators
• Improved control authority and longevity
• Low cost, flexible “peel-and-stick” construction
Power Supply
• Custom inverter
• Working towards low-profile, integrated transformers
Demonstration
• Full-scale demonstration with first-generation actuator
• Measured increased CP, projected to yield a 13% increase in AEP
Neal E. Fine, PhD 07/06/15 10/10
Editor's Notes
This video was shot in Navatek’s wind tunnel. It shows a wing section which is a geosym of a wind turbine blade built by Renewegy, at the seven-tenths radius. On the left of the frame, just off camera, is a low-voltage hot wire. When the wire is coated with oil and heated electrically, the oil vaporizes, forming the white streak lines. A pair of plasma actuators is mounted on the suction side of the blade between mid-chord and the trailing edge. As you can see, when the plasma is on, the flow goes from stalled to fully attached. Because this is a low-speed demonstration, it is in a sense an exaggeration of what goes on at full scale Reynolds numbers. Nevertheless, it is a very quick way of demonstrating what we are trying to do with active flow control – mitigate boundary layer separation, delaying stall and increasing the maximum lift coefficient.
The graph on the right shows a sample lift polar for the VP20 section shown in the previous slide. The improved aerodynamic performance leads to an increased energy capture. Depending on the platform and system design, we project an increase in CP in Region 2 between 5 and 15%, resulting in increased AEP of 5-10%. For pitch-controlled turbines, we expect that plasma flow control would reduce the dependence on pitch control. Ultimately, we envision a Region 3 role as well in reacting to gusts to reduce fatigue loads. This is an area that has not been fully explored.
The Office of Naval Research sponsored a demonstration project during the 2012-2015 time frame, performed by Navatek with Neal Fine as the PI. Navatek purchased a pair of Renewegy VP20 wind turbines and mounted them on the wing walls of the Company’s dry dock in Honolulu. The demonstration project began with laboratory testing and performance predictions, and culminated with a series of full-scale demonstrations.
The picture shows the two identical VP20 turbines mounted on the wing walls of a drydock in Honolulu. The shore side turbine (on the right) includes the prototype plasma flow control system. A hydraulic lift kit allows the tower to be tilted down for installation and servicing. The VP20 is a variable-speed, pitch controlled turbine, which is unusual for this size. We chose this turbine in part because the manufacturers attempted to incorporate control and monitoring technology usually only seen on the large industrial turbines.
This schematic shows the general layout of the system. The power inverter and controller are mounted near the base of the tower. We also use a variable autotransformer (commonly known as a Veriac) for manual voltage control. The inverter connects to a trunk cable carrying a high frequency signal at roughly 200 V and 3 kHz. That passes through a slip ring and connects to a set of HV transformers mounted in the hub. This design prevents us from passing a high voltage signal through the slip ring (in exchange for higher current). Each transformer serves one blade’s worth of actuators, which consisted of five independent actuators daisy-chained from roughly 20% span to roughly 95% span.
This picture shows transformers and inductor mounted in the hub beneath the nose cone. The red component beneath the blades is the custom slip ring.
This picture shows the actuators glowing against the night sky, following our second-phase installation.
These are some of the key accomplishments to date. We have put together a state-of-the-art plasma lab at Navatek, including a custom-built low-speed wind tunnel. We have advanced actuator technology along a track that will lead to a low-cost, flexible “peel-and-stick” actuator with the highest control authority and longevity in the nascent industry. We developed a new inverter that is also designed to keep costs low, and could support a future design where the transformers are integrated with the actuators. We performed a full-scale demonstration with the first-generation actuator, and measured an increase in CP that’s projected to yield a 13% increase in AEP.
