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- Desenvolvimento de uma instalação experimental, e sistema PIV, para o ensaio de tubeiras de efeito Coanda com atuadores a plasmaPublication . Rodrigues, Frederico Miguel Freire; Marques, José Carlos PáscoaEsta dissertação teve como objetivo o estudo experimental do comportamento do escoamento na geometria HOMER, em particular com o intuito de validar a capacidade desta geometria defletir o escoamento em função de um diferencial de caudais. Este trabalho fez parte integrante do Projeto Europeu ACHEON. A geometria CAD 3D fornecida pelos restantes parceiros do projeto foi reproduzida, e montou-se uma instalação experimental que permitiu a realização de diferentes tipos de ensaios. Desenvolveu-se ainda, de raiz, um sistema de análise do escoamento baseado na técnica de medição PIV, o qual permitiu a obtenção do campo de velocidades do escoamento à saída da tubeira. Os resultados das medições PIV mostraram que a capacidade da tubeira HOMER em defletir o escoamento é fortemente afetada pelos efeitos 3D do escoamento. Para reduzir a influência dos efeitos 3D do escoamento implementaram-se alhetas nas entradas de ar da tubeira. As alhetas mostraram-se eficazes na redução da influência dos efeitos 3D, nomeadamente reduzindo a velocidade tangencial, e permitiram a obtenção de melhores resultados para a deflexão do escoamento. Os resultados obtidos com e sem alhetas foram comparados e discutidos. Testaram-se atuadores de plasma de DBD, que foram posteriormente implementados na superfície Coanda da tubeira HOMER, de modo a aumentar o ângulo de deflexão do escoamento. Os atuadores de plasma de DBD mostraram-se eficazes, contribuindo para maior adesão do escoamento à superfície Coanda e um consequente aumento do ângulo de deflexão máximo do escoamento. Foram captadas imagens da visualização do escoamento que permitiram comparar a deflexão do jato com e sem atuadores de plasma. Os resultados deste trabalho experimental foram, ao longo do seu desenvolvimento, apresentados aos restantes parceiros do projeto.
- Development of a Background-Oriented Schlieren (BOS) System for Thermal Characterization of Flow Induced by Plasma ActuatorsPublication . Moreira, Miguel; Rodrigues, Frederico; Cândido, Sílvio; Santos, Guilherme; Pascoa, JoséCold climate regions have great potential for wind power generation. The available wind energy in these regions is about 10% higher than in other regions due to higher wind speeds and increased air density. However, these regions usually have favorable icing conditions that lead to ice accumulation on the wind turbine blades, which in turn increases the weight of the blades and disrupts local airflow, resulting in a reduction in wind turbine performance. Considering this problem, plasma actuators have been proposed as devices for simultaneous flow control and deicing. These devices transfer momentum to the local airflow, improving the aerodynamic performances of the turbine blades while producing significant thermal effects that can be used to prevent ice formation. Considering the potential application of plasma actuators for simultaneous flow control and deicing, it is very important to investigate the thermal effects induced by these devices. However, due to the significant electromagnetic interference generated by the operation of these devices, there is a lack of experimental techniques that can be used to analyze them. In the current work, a background-oriented Schlieren system was developed and is presented as a new experimental technique for the thermal characterization of the plasma-induced flow. For the first time, the induced flow temperatures are characterized for plasma actuators with different dielectric materials and different dielectric thicknesses. The results demonstrate that, due to the plasma discharge, the temperature of the plasma-induced flow increases with the increase of the applied voltage and may achieve temperatures five times higher than the room temperature, which proves the potential of plasma actuators for deicing applications. The results are presented and discussed with respect to the potential application of plasma actuators for simultaneous flow control and deicing of wind turbine blades.
- Modelação experimental para otimização de atuadores a plasma com aplicações em termofluidodinâmicaPublication . Rodrigues, Frederico Miguel Freire; Marques, José Carlos Páscoa; Trancossi, MicheleOs atuadores a plasma são dispositivos de grande simplicidade mas com capacidade comprovada para aplicações nas áreas de controlo ativo de escoamentos e de transferência de calor. Estes dispositivos inovadores apresentam diversas características bastante atrativas tais como, fabricação de elevada simplicidade, peso reduzido, rápido tempo de resposta, baixo consumo de potência e robustez. O presente trabalho foca-se no estudo de atuadores a plasma tendo em vista a otimização destes dispositivos e a sua aplicação em termofluidodinâmica. A interferência eletromagnética gerada pela formação de plasma impossibilita a utilização de diversas técnicas de laboratório convencionais. Como tal, foi idealizada uma instalação experimental baseada em diversas técnicas experimentais que permitem ultrapassar os problemas causados pela interferência eletromagnética. Para além disso, uma técnica experimental não-intrusiva baseada em princípios calorimétricos foi idealizada tendo em vista a quantificação da potência calorifica gerada pela atuação do plasma. Recorrendo à instalação experimental concebida, foi realizada uma análise exaustiva sobre o escoamento induzido por atuadores a plasma de barreira dielétrica de descarga (DBD), incluindo visualizações do jato de parede induzido e medições das velocidades do escoamento. A influência da espessura da camada dielétrica foi avaliada, bem como a influência de diferentes materiais dielétricos. Na análise de diferentes materiais dielétricos, três materiais dielétricos foram propostos como materiais alternativos para a fabricação de atuadores a plasma. A potência mecânica e a eficiência mecânica foram também quantificadas para diferentes espessuras de camada dielétrica e diferentes materiais dielétricos. O conceito de uma nova configuração de atuadores a plasma, designada de “Stair Shaped Dielectric Barrier Discharge Plasma Actuator”, foi apresentado e testado experimentalmente. Foi demonstrado que esta nova configuração permite melhorar a eficiência de atuadores a plasma, sendo que também apresenta uma excelente durabilidade da camada dielétrica. Uma possível aplicação de atuadores a plasma dentro da área do controlo ativo de escoamentos consiste na redução da esteira de veículos. Como tal, um corpo “Ahmed” e um “Backward-facing step” foram testados em túnel de vento e a capacidade de atuadores a plasma para redução da esteira foi demonstrada. As propriedades térmicas de atuadores a plasma foram também analisadas durante o presente trabalho. A potência calorífica gerada por atuadores a plasma DBD foi quantificada e os mecanismos de geração de calor por detrás do funcionamento de atuadores a plasma foram explicados. Os campos de temperatura à superfície de diferentes atuadores a plasma foram obtidos através de termografia de infravermelhos para condições de ar quiescente e também sob influência de um escoamento externo imposto. A influência do escoamento externo no campo de temperaturas de superfície foi também discutida. Um novo sistema de proteção de gelo e controlo de escoamento baseado na impressão de atuadores a plasma DBD de descarga por deslizamento foi proposto.
- Dielectric barrier discharge plasma actuators based on thermosetting composites for flow control in wind turbines bladesPublication . Nunes-Pereira, João; Rodrigues, Frederico; Abdollahzadehsangroudi, Mohammadmahdi; Pina dos Santos, Paulo Sérgio; Silva, Marco; Pereira Silva, A; Pascoa, Jose; Lanceros-Mendez, SenentxuThe massive use of fibre reinforced plastics (FRP) in several industrial sectors such as aeronautics, aerospace, or wind turbines, raises serious environmental concerns with respect to the end-of-life of these structures, based on their poor recyclability. The low density of FRP gives it outstanding specific properties, such as strength and stiffness, when compared to materials with high recyclability rates, such as metals1. FRP find several applications in structures in which the aerodynamic performance is of extreme importance to guarantee a proper operation. In this sense, to endow these structures with the ability to control or modulate the flow around their surface could be an extraordinary feature to improve the performance of the structure, thus saving considerable amounts of energy and increasing its useful life cycle, contributing in this sense also to reduce the environmental impact of the materials. This work is focused on the development of dielectric barrier discharge (DBD) plasma actuators supported on fibre reinforced thermosetting composites, which can be used in manufacturing of wind turbine blades: epoxy resin and glass, aramid (Fig. 1) and natural flax fibres. DBD plasma actuators are electrohydrodynamic devices capable of generating induced flows of a few m/s through nonthermal plasma, that can be successfully leveraged for flow control applications2, 3. The characterization of the system was carried out in terms of mechanical (flexural strength, strain and stiffness), electrical (power consumption, capacitance, charge-discharge cycles) and electromechanical (induced flow velocity, electromechanical power and efficiency) properties. The results showed the multifunctionality of the composites, demonstrating their suitability for the application, in particular, the epoxy/glass composite with a bending stress of ≈600 MPa, which obtained an induced flow velocity of ≈2.1 m/s with a power consumption of ≈15.1 W, when powered by an AC signal of 11 kVpp and 24 kHz.
- Multifunctional Ceramics for Aeronautical and Aerospace ApplicationsPublication . Shvydyuk, Kateryna; Nunes-Pereira, João; Rodrigues, Frederico; Pascoa, Jose; Lanceros-Mendez, Senentxu; Pereira Silva, AIn the areas of aeronautics and aerospace, ceramic composites play an essential and increasing role due to their superior performance and tailorable properties, exhibiting highly specialized mechanical, thermal, and electric features1. Their main applications include thermal protection systems (TPS), thermal barrier coatings (TBC), and dielectric barrier discharge (DBD) plasma actuators, both for instrumentation and control purposes2. This work reports the manufacture and characterization of three ceramic composites capable of fulfilling the multifunctional ceramic condition according to the aforementioned applications. Accordingly, MgO-Al2O3 (MA), MgOCaZrO3 (MCZ), and Y2O3 stabilized ZrO2 (YSZ) are introduced for TPS, TBC, and DBD dielectric elements. To this aim, MA, MCZ, and YSZ ceramic composites were fabricated via a sequential process, encompassing the selection of raw powders and milling, die pressing, and sintering. Further, the samples were polished for surface optimization. Overall, the results obtained, including mechanical (Young’s and shear moduli, flexural strength, hardness, and fracture toughness), thermal (thermal conductivity and thermal expansion (CTE)), and electrical (dielectric constant) properties, report evidence that the developed ceramics show suitable multifunctional characteristics and therefore fulfil the aeronautical and aerospace demands for increased materials performances. The combined analysis of the Young’s and shear moduli (Fig.1a) with the CTE – the latter over a wide range of temperatures (Fig. 1b) – allows concluding that the cost-effective and widely used alumina appears suitable for bulk monolithic (TPS) and joint applications (TPS, TBC, and DBD).
- Plasma Actuators Based on Alumina Ceramics for Active Flow Control ApplicationsPublication . Rodrigues, Frederico; Shvydyuk, Kateryna; Nunes-Pereira, João; Pascoa, Jose; Silva, AbilioPlasma actuators have demonstrated great potential for active flow control applications, including boundary layer control, flow separation delay, turbulence control, and aircraft noise reduction. In particular, the material used as a dielectric barrier is crucial for the proper operation of the device. Currently, the variety of dielectrics reported in the literature is still quite restricted to polymers including Kapton, Teflon, poly(methyl methacrylate) (PMMA), Cirlex, polyisobutylene (PIB) rubber, or polystyrene. Nevertheless, several studies have highlighted the fragilities of polymeric dielectric layers when actuators operate at significantly high-voltage and -frequency levels or for long periods. In the current study, we propose the use of alumina-based ceramic composites as alternative materials for plasma actuator dielectric layers. The alumina composite samples were fabricated and characterized in terms of microstructure, electrical parameters, and plasma-induced flow velocity and compared with a conventional Kapton-based actuator. It was concluded that alumina-based dielectrics are suitable materials for plasma actuator applications, being able to generate plasma-induced flow velocities of approximately 4.5 m/s. In addition, it was verified that alumina-based ceramic actuators can provide similar fluid mechanical efficiencies to Kapton actuators. Furthermore, the ceramic dielectrics present additional characteristics, such as high-temperature resistance, which are not encompassed by conventional Kapton actuators, which makes them suitable for high-temperature applications such as turbine blade film cooling enhancement and plasma-assisted combustion. The high porosity of the ceramic results in lower plasma-induced flow velocity and lower fluid mechanical efficiency, but by minimizing the porosity, the fluid mechanical efficiency is increased.
- Long-lasting ceramic composites for surface dielectric barrier discharge plasma actuatorsPublication . Shvydyuk, Kateryna; Rodrigues, F.F.; Nunes-Pereira, João; Pascoa, José; Lanceros-Mendez, Senentxu; Silva, A PereiraThe developed research presents a novel experimental study of the cost-effective MgO-Al2O3, MgO-CaZrO3 perovskite, and thermally stable YSZ ceramic composites for DBD plasma actuators in aerospace applications. This study focuses on the implementation of ceramic DBD plasma actuators for aerodynamic flow control and ice creation mitigation. For this purpose, electrical power consumption analysis, induced flow velocities assessment, and mechanical and thermal characterization were performed. MgO-Al2O3 presented higher induced velocities than its zirconia-based counterparts of up to 3.3 m/s, and lower heat dissipation, achieving a ceiling temperature of 46 ºC, being thereby the best-suited candidate for active flow control mechanisms. In contrast, YSZ had very high-power consumption translated into a maximum surface temperature of 155.4 ºC, establishing itself for ice mitigation. This extensive research evinces that the strategic combination of the developed ceramics’ thermomechanical, thermoelectric, and electromechanical properties allows them to be a promising breakthrough material for DBD plasma actuators.
- Improved performance of polyimide Cirlex‐based dielectric barrier discharge plasma actuators for flow controlPublication . Nunes-Pereira, João; Rodrigues, Frederico Miguel Freire; Abdollahzadehsangroudi, Mohammadmahdi; Pascoa, José; Lanceros-Mendez, SenentxuDielectric barrier discharge (DBD) plasma actuators are simple electrohydrodynamic devices, which are able to provide effective aerodynamic control. One of the main components of these devices is the thin dielectric layer, which allows to separate and prevent the arc between the high-voltage electrodes. Different materials can be used as dielectric layer to reduce the power consumption or boost the flow controlling effect of the actuators. In this context, this report presents a comparative study of two commercial polyimides, Kapton and Cirlex, used as dielectric layer of surface DBD plasma actuators. The electrical, dielectric, mechanical, electromechanical, and thermal properties were obtained to evaluate overall performance. It was verified that Cirlex (8.3 W) consumes less power than Kapton (21.3 W) to generate higher induced flow velocity of ≈3.4 m/s for an input voltage of 11 kVpp and 24 kHz. During one AC cycle at 11 kVpp the charge transferred for Cirlex (70 nC) is lower than for Kapton (100 nC), as well as the dielectric breakdown voltage to ignite the plasma discharge, 1.5 and 2.2 kVpp, respectively. The Cirlex DBD presents a higher voltage operation limit (at least 14 kVpp) and a more regular plasma discharge, which results in a more homogenous thermal profile and temperature distribution during its operation. The Cirlex actuator delivered higher mechanical power (6.2 mW) and achieved higher electromechanical efficiency (0.004%). The polyimide Cirlex proved to be a suitable alternative for Kapton to fabricate DBD plasma actuators for flow control with improved performance.
- Review of Ceramic Composites in Aeronautics and Aerospace: A Multifunctional Approach for TPS, TBC and DBD ApplicationsPublication . Shvydyuk, Kateryna O.; Nunes-Pereira, João; Rodrigues, Frederico Miguel Freire; Silva, AbilioThe quest for increased performance in the aeronautical and aerospace industries has provided the driving force and motivation for the research, investigation, and development of advanced ceramics. Special emphasis is therefore attributed to the ability of fine ceramics to fulfill an attractive, extreme, and distinguishing combination of application requirements. This is impelled by ensuring a suitable arrangement of thermomechanical, thermoelectric, and electromechanical properties. As a result, the reliability, durability, and useful lifetime extension of a critical structure or system are expected. In this context, engineered ceramic appliances consist of three main purposes in aeronautical and aerospace fields: thermal protection systems (TPS), thermal protection barriers (TBC), and dielectric barrier discharge (DBD) plasma actuators. Consequently, this research provides an extensive discussion and review of the referred applications, i.e., TPS, TBC, and DBD, and discusses the concept of multifunctional advanced ceramics for future engineering needs and perspectives.
- Recent Developments on Dielectric Barrier Discharge (DBD) Plasma Actuators for Icing MitigationPublication . Rodrigues, Frederico Miguel Freire; Abdollahzadehsangroudi, Mohammadmahdi; Nunes-Pereira, João; Pascoa, JoséIce accretion is a common issue on aircraft flying in cold climate conditions. The ice accumulation on aircraft surfaces disturbs the adjacent airflow field, increases the drag, and significantly reduces the aircraft’s aerodynamic performance. It also increases the weight of the aircraft and causes the failure of critical components in some situations, leading to premature aerodynamic stall and loss of control and lift. With this in mind, several authors have begun to study the thermal effects of plasma actuators for icing control and mitigation, considering both aeronautical and wind energy applications. Although this is a recent topic, several studies have already been performed, and it is clear this topic has attracted the attention of several research groups. Considering the importance and potential of using dielectric barrier discharge (DBD) plasma actuators for ice mitigation, we aim to present in this paper the first review on this topic, summarizing all the information reported in the literature about three major subtopics: thermal effects induced by DBD plasma actuators, plasma actuators’ ability in deicing and ice formation prevention, and ice detection capability of DBD plasma actuators. An overview of the characteristics of these devices is performed and conclusions are drawn regarding recent developments in the application of plasma actuators for icing mitigation purposes.