. Caracterização física, aspectos morfológicos, comportamentos térmico e mecânico do pecíolo do miriti como um material potencial para aplicações em pás de turbinas eólicas.

Abstract

In many small wind turbine blades, the internal space between the laminated shells is filled with a core material. In this context, with the aim of enabling the application in both small and large blades, this thesis presents the petiole of the miriti palm (PMP) as a potential material for such applications. PMP is abundant in the Amazon region, and its harvesting does not harm the palm, as the petiole regrows, making the process fully sustainable. This could play an important role in enhancing the sustainability of wind turbine manufacturing. The physical properties, morphological aspects, and thermal and mechanical behaviors of PMP were determined and compared to balsa wood (BW). Additionally, the advantages of using the easily worked petiole for the core in manufacturing were considered, as demonstrated by the construction of a 0.598 m blade and starting performance tests of the turbine in both computational simulations and wind tunnel experiments. The results showed that PMP is about 50% less dense than BW. Consequently, turbine starting simulations indicated that the low density of the small blade made from PMP reduces starting time by 10% compared to EPS and by 42% compared to BW. While PMP and BW have similar morphological aspects as they are natural materials, BW tends to absorb about 3.6% more moisture and around 9% more water than PMP. The thermal behavior of PMP shows stability up to approximately 200°C, making it suitable for most wind turbine manufacturing processes. Regarding mechanical properties such as tensile, compression, bending, and shear strength, both BW and PMP exhibited elastoplastic behavior. Although BW generally possesses higher mechanical properties than PMP, the specific properties of PMP are greater than those of BW, except in cases where the load application does not align with the vascular bundle direction. For instance, the specific elastic strength and specific elastic modulus in tensile with a load applied at 90° in relation to the vascular bundle and in tensile with a load applied at 0° in relation to the vascular bundle of the PMP are approximately 13.5%, 3%, 30% and 61% higher than those of the BW, respectively. PMP’s specific elastic strength in GS compression is approximately 18.5% higher than BW. In shear strength, the specific elastic strength and specific modulus of elasticity of PMP are 20% and 54.5% higher compared to BW. Fatigue results indicate that PMP has a fatigue life of around 106 cycles. Wind tunnel tests showed that, regardless of wind speed, the best results for power coefficient, torque, and thrust were observed in 6-blade configurations, with values of 0.3083, 0.1224, and 2.2993 for λopt equal to 2.519. In analyzing the experimental results for rotation, thrust, torque, and kinetic energy ratio during turbine starting, the periods through which the turbine transitions between transient and steady states were observed, aligning with literature findings. The results presented in this work show that PMP has potential for application in wind turbine blades, as the combination of sustainable materials with significant specific mechanical properties, such as low density, has the potential to improve turbine design, reduce starting time, and extend the high-efficiency operating range.