Aerodynamic devices to improve the performance of a WTG

How added devices modify the performance of fixed-pitch wind turbine generators? Information gathered from a maintenance company, an experimental wind farm and a university was used to complete this thesis.

Master's thesis | 2017
CFD simulation image of a wind turbine blade

OBJECTIVE

The objective of this study was the analysis of the power performance of a fixed-pitch wind turbine generator and evaluate the convenience of adding devices to modify the aerodynamics of the blades.

I did this project while working in IM Future, a wind turbine generator maintenance company from Galicia, Spain. We wanted to compare data from the experimental wind farm of Sotavento in order to quantify the effects of the modifications.

BACKGROUND

Within the same wind farm normally there is only one WTG model. This is due to easier operation and maintenance. However, different individual WTG may have different performance because of their specific location in the wind farm or because blade surface deformations over their lifetime.

WTGs have a nominal power that they are optimized for and a power curve that shows how much power they generate for a given wind speed. The different performances that may happen in individual wind turbines for any reason will normally lower the total power produced.

power curves diagram

If the WTG under-produces it will never reach the nominal power, and obviously produce less energy. If it overproduces it will reach the nominal power too soon, at wind speeds lower than expected. As soon as the nominal power is exceed by a security margin, the WTG will need to shut down and loose the high and more energetic wind speed that it was designed for, thus producing less energy too.

AERODYNAMIC DEVICES

Dino-tails

This are small plastic plates that look like a saw. They increment the tip cord and an the overall lift of the blade. They move the curve up.

power curves diagram

Vortex generators

They are often used in blade design, so they are already installed in many WTG models. They create vortex that bring energy back to the boundary layer, practically attaching the flow to the surface. They can delay the flow separation and the stall of the blade. They extend the power curve.

power curves diagram

Stall lists

They are plastic lists normally with a triangle cross-section placed in the leading edge of the blades. At a certain angle, they induce a small detached bubble that makes the blade stall earlier. They lower the power curve.

power curves diagram

EMPIRICAL DATA

Checking some of the data from the WTG of Sotavento we could see the clear differences of performance before and after the install of the devices.

The first one is a WTG that overproduced, missing out higher speed winds and power generation. In the graph we can see how after the installment we have power production at higher wind speeds.

real data from a wind turbine generator

The second one under-produced, never reaching the expected power. After the install of the dino-tails we see an increase of the power generated in the higher wind speeds.

real data from a wind turbine generator

CONCLUSIONS AND WARNINGS

It is clear that under an easy analysis, under-performing WTG can be improved with easy and cheap aerodynamic devices. However, this need to be done with great care. Any aerodynamic modification implies a load and stress modification that has to be also analyzed. Extending the power generated by a WTG beyond the designed nominal value would certainly lead to a mechanical or structural failure sooner or later.