Wind test systems are the most advanced testing systems used to evaluate rotor blade fatigue and strength. During the testing process, blades are bent in a flap wise direction using a cycle that is of the same natural frequency during its operations. It is a long process, and it generally takes about 5 million full cycles to bring about the results and analyse the strength of blades and also the fatigue that these blades can withstand.

The natural frequency is the frequency that is measured by the back-and-forth oscillation of the blade when pushed from one direction to a specific direction. The natural frequencies in the flatwise and edgewise directions are different. The blade is substantially stiffer in the edgewise direction; hence edgewise bending has a greater natural frequency compared to the flaps frequency.

An electric motor attached to each blade swings weight up and down, setting it in motion. So, the foundations that support the blade socket must be very strong in a wind test system. The socket foundation for a large blade is generally made of 2,000 tonnes of concrete to accommodate the oscillation frequency.

Denmark follows a strict policy for testing rotor blade strength and fatigue properties. The wind test systems consist of physical testing of rotor blades to check strength properties via static testing and fatigue properties via fatigue testing. Once the results are up to the mark, the rotor blades are then passed through the test.

The objective of wind test systems is to verify that laminations in the rotor blade are safe. The process ensures that the layers of the rotor blade do not break or delaminate or separate from each other when exposed to repeated stress.

Let us discuss the essential features of a wind test system and how the process can help manufacturing companies ensure the best products for end-use.

Rotor Blade Materials

Rotor blades are made of a matrix which is a combination of materials called Glass fibre reinforced polyester (GRP). In GRP, glass fibre mats are impregnated with polyester. After the impregnation process, the polyester is made to harden to create a substantially strong material. Epoxy is also used at times in place of polyester to create the matrix.

The process of building the basic matrix can be different in different cases. It can be either made wholly or partially using carbon fibre, a lighter but costlier material to achieve a material with much higher strength or rotor blades. In the case of large rotor blades, wood and epoxy laminates are also used.

Monitoring Fatigue

In wind test systems, computers are set to continuously monitor the strain gauge results of the blades. The results give an outline of the nonlinear pattern variations, which eventually reveals the damages (if any) that occur during the testing phase.

Static Testing of Rotor Blades

Static testing is done on rotor blades to check the strength of the material. The test is performed to check the ability of the blades to withstand extreme loads. It is done by bending the blades with a very large force after it has passed through the rigorous fatigue testing phase. The static testing results reveal the blades’ ability to withstand stress after prolonged exposure during its operation.

Modal Forms of Rotor Blade Vibrations

Denmark follows a stringent rotor blade testing process where different modal forms of vibrations are checked for each blade. A special type of equipment is used during the testing process to increase the blade vibrations to different frequencies and in different directions to evaluate the blade's effectiveness.

It is essential to check the different forms of vibration frequencies in rotor blades. Turbine manufacturing companies can ensure that the turbine where the blades will be mounted for final usage does not have the same natural frequency as that of the rotor blades. If the frequencies match with each other, the whole turbine structure will have a higher level of resonance, which eventually will lead to undampened vibrations and cause damage to the whole turbine.

Infrared Inspection (Thermography)

The wind testing system uses infrared cameras to identify the local build-up of heat in the blade. The results may suggest a structural dampening in an area. The test specifically reveals areas in the blade where designers have purposefully laid out fibres to convert bending energy into heat to stabilise the blade. The test also reveals areas where delamination of fibres has happened and if the blade approaches its breaking limit.

The Final Wrap

Many turbine manufacturing companies find it difficult to incorporate the entire wind test systems in their own facility. It is best to take external help in conducting such tests and ensure the highest degree of results.

Companies like R&D Test systems A/S offer the superior infrastructure to carry out structural tests of wind turbines and blades. Companies from different sectors in the wind industry in need of a wind testing system can connect with the team and get turnkey solutions for large-scale dynamic test systems.

You may get solutions varying from selecting the most suitable machine testing to testing the major components of a complete cycle of rotor blade testing. It is eminent that the next generation of wind turbines is set to become robust, and the need for an external testing facility will grow. So, if you want to bag the best solutions in the whole process of wind testing for rotor blades, it is best to connect with R&D Test systems A/S.

You may discuss your specific requirements for the wind test systems and accordingly get a rate quotation for the same. However, be sure that you will get the best solutions when you collaborate with the expert team of R&D Test systems A/S as they are equipped with years of experience in the wind industry and also use state-of-the-art infrastructure to carry out the full-cycle testing phase of rotor blades and other parts in the turbine.

Speak to the representatives of R&D Test systems A/S to know more.