Santhosh Chandrabalan / Technical Business Development Leader / 3M / www.3M.com
The design of wind-turbine blades cannot be exclusively aimed at maximizing aerodynamics. The practicalities of manufacturing, transporting, and installing the blades, as well as other limitations, require tradeoffs in aerodynamic efficiency. These tradeoffs equate to a loss in Annual Energy Production (AEP) and can impact the bottom line for turbine owners.
The primary challenge lies at the root and twist of the blade, which has suboptimal aerodynamic properties that contribute to undesired airflow separation, known as aerodynamic stall. Additional real-world factors such as surface roughness and leading-edge erosion can worsen the problem. Some of the major losses in efficiency, due to design compromises, can be offset by vortex generators (VGs). These small attachments, typically made from metal or plastic, regulate the boundary-layer airflow by helping it stay attached to the turbine blade for a longer period thereby, increasing efficiency.
Real-world challenges for vortex generators
While VGs seem like an excellent solution in principle, they have been associated with several problems in practice. Because of the unique designs and properties of wind-turbine blades, a VG should be customizable. Factors such as wind speeds, can vary the performance of VGs, and must be installed correctly with a sturdy attachment mechanism. Liquid adhesives have traditionally been used for installations. Most adhesives are, however, not robust enough or are too brittle to stand up to flexing forces caused by differences in the material coefficient of thermal expansion and the harsh weather conditions that damage the blade over time.
This combination of issues explains why VGs typically have not lived up to their potential. Replacing VGs on a regular basis is neither cost effective nor efficient for owners and operators. On a standard installation where the design is not customized, a VG may fail well before the two-year mark. The demands of the environment and the application are simply too great.
A custom-designed solution
It is this set of challenges that 3M Wind Vortex Generators help address. By combining optimal design and installation processes with an innovative and efficient attachment technology, These VGs provide the long-term reliability needed for owners to see a potential return on their investment.
To create this solution, we partnered with specialists in aerodynamic technology to custom fit each VG. Aerodynamic studies allow tailoring to a blade, which improves performance and flow around the surface. This helps reduce flow separation and increases the performance of the entire turbine in terms of power, loads, and service life.
What’s more, the VGs are made of a highly durable thermoplastic with dimensional stability and strength that has a proven track record of superior weathering resistance. They also easily attach using 3M Acrylic Foam Tapes. These tapes provide increased adhesive strength, as well as the conformability needed to accommodate the flexing and residual forces acting on the turbine-blade surface. While a traditional bonding system is insufficiently durable for long-term success on a turbine blade, acrylic foam tapes provide the flexibility needed for a variation of forces, temperatures, and other weather conditions. In fact, service life prediction studies obtained through weathering testing of the tapes in extreme climates ranging from Minnesota to Arizona have shown that they retain around 95% of their functional properties even after five years.
This helps VGs maximize a blade’s full potential. In case studies, AEP increases of 2 to 3% have been confirmed, and increases of up to 5% are theoretically possible for specific blade types and installations. Additionally, 3M and its partners work with customers to perform trial installations which provide the opportunity for a customized preview of their potential AEP increases before committing to a full-scale project.
The average turnaround time is one day per turbine, which helps turbine owners to see an appreciable boost in AEP with minimal downtime. In consequence, VGs are an economically viable upgrade that can be counted on to maximize ROI and reduce the cost of wind energy.
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