Departamento de Engenharia Electromecânica
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Browsing Departamento de Engenharia Electromecânica by Author "Abdollahzadehsangroudi, Mohammadmahdi"
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- Analysis and development of numerical methodologies for simulation of flow control with dielectric barrier discharge actuatorsPublication . Abdollahzadehsangroudi, Mohammadmahdi; Marques, José Carlos Páscoa; Oliveira, Paulo Jorge dos Santos Pimentel deThe aim of this thesis is to investigate and develop different numerical methodologies for modeling the Dielectric Barrier discharge (DBD) plasma actuators for flow control purposes. Two different modeling approaches were considered; one based on Plasma-fluid model and the other based on a phenomenological model. A three component Plasma fluid model based on the transport equations of charged particles was implemented in this thesis in OpenFOAM, using several techniques to reduce the numerical issues. The coupled plasma-fluid problem involves wide range of length and time scales which make the numerical simulation difficult. Therefore, to obtain stable and accurate results in a reasonable computational run time, several numerical procedures were implemented including: semi-implicit treatment of coupling of Poisson equation and charge density equation, super-time-stepping and operator splitting algorithm. We examined our code for a constant positive voltage, testing for the dependency of the behavior of the current density to the selected numerical scheme. In addition, although there is no clear numerical or experimental benchmark case for DBD plasma actuator problem, the developed plasma solver was compared quantitively and qualitively with several numerical works in the literature. Afterward, the developed numerical methodology was used to explore the possibility of influencing the flow, with higher speed, using nano-second (NS) pulsed DBD plasma actuator. Therefore, the interaction of the transonic flow and actuation effects of DBD plasma actuator with nano second pulsed voltage was simulated. The effect of gas heating and body force was calculated by the plasma solver and was supplied into the gas dynamic solver for simulating the flow field. Moreover, the results of the plasma fluid model were used to develop an energy deposition model. It was shown that the energy deposition model is able to capture the main features of the effect of NS DBD plasma actuators correctly, with less computational time. It was also shown that fast energy transfer, from plasma to fluid, leads to the formation of micro-shock waves that modify locally the features of the transonic flow. Although the numerical efficiency of the plasma fluid model was improved, the computational cost of simulating the effect of DBD plasma actuator on a real scale flow situation was still high. Therefore, a simple model for plasma discharge and its effect on the flow was developed based on scaling of the thrust generated by DBD plasma actuators. The scaled thrust model correctly predicts the nonlinear dependency of the thrust produced and the applied voltage. These scales were then introduced into a simple phenomenological model to estimate and simulate the body force distribution generated by the plasma actuator. Although the model includes some experimental correlations, it does not need any fitting parameter. The model was validated with experimental results and showed better accuracy compared to previous plasma models. Using a simple phenomenological model that was developed here, a numerical study was conducted to investigate and compare the effect of steady and unsteady actuation for controlling the flow at relatively high Reynolds number. Firstly it was shown that the size of the time-averaged separation bubble is greatly reduced and the flow structure is sensitive to the frequency of burst modulation of DBD plasma actuators. The results also confirmed that in the case of unsteady actuation, the burst frequency and burst ratio are crucial parameters for influencing the capability of the actuators to control the flow. It was found that burst frequencies near the natural frequencies of the system were able to excite the flow structure in a resonance mode. This observation also confirmed that with proper frequencies of excitation, the flow structure can be well rearranged and the flow losses can be reduced. In the end, Plasma actuators were used for controlling the flow over the Coanda surface of the ACHEON nozzle. When the plasma actuator was used, it was possible to postpone separation of the flow and increase the deflection angle of the exit jet of the nozzle. To find the optimum position of the actuators, seven DBD actuators in forward forcing mode were placed over the Coanda surface considering the numerically obtained separation points. Results show that when the actuator is placed slightly before the separation point, enhanced thrust vectorizing with the use of DBD actuator is achievable. Preliminary results of the experiments agree with planned/foreseen deflection angle obtained from numerical computation.
- Comparative Evaluation of Dielectric Materials for Plasma Actuators Active Flow Control and Heat Transfer ApplicationsPublication . Rodrigues, Frederico; Nunes-Pereira, João; Abdollahzadehsangroudi, Mohammadmahdi; Pascoa, Jose; Lanceros-Mendez, SenentxuDielectric Barrier Discharge (DBD) plasma actuators are simple devices with great potential for active flow control applications. Further, it has been recently proven their ability for applications in the area of heat transfer, such as film cooling of turbine blades or ice removal. The dielectric material used in the fabrication of these devices is essential in determining the device performance. However, the variety of dielectric materials studied in the literature is very limited and the majority of the authors only use Kapton, Teflon, Macor ceramic or poly(methyl methacrylate) (PMMA). Furthermore, several authors reported difficulties in the durability of the dielectric layer when the actuators operate at high voltage and frequency. Also, it has been reported that, after long operation time, the dielectric layer suffers degradation due to its exposure to plasma discharge, degradation that may lead to the failure of the device. Considering the need of durable and robust actuators, as well as the need of higher flow control efficiencies, it is highly important to develop new dielectric materials which may be used for plasma actuator fabrication. In this context, the present study reports on the experimental testing of dielectric materials which can be used for DBD plasma actuators fabrication. Plasma actuators fabricated of poly(vinylidene fluoride) (PVDF) and polystyrene (PS) have been fabricated and evaluated. Although these dielectric materials are not commonly used as dielectric layer of plasma actuators, their interesting electrical and dielectric properties and the possibility of being used as sensors, indicate their suitability as potential alternatives to the standard used materials. The plasma actuators produced with these nonstandard dielectric materials were analyzed in terms of electrical characteristics, generated flow velocity and mechanical efficiency, and the obtained results were compared with a standard actuator made of Kapton. An innovative calorimetric method was implemented in order to estimate the thermal power transferred by these devices to an adjacent flow. These results allowed to discuss the ability of these new dielectric materials not only for flow control applications but also for heat transfer applications.
- Comparison of DBD plasma actuators flow control authority in different modes of actuationPublication . Abdollahzadehsangroudi, Mohammadmahdi; Páscoa, J.C.; Oliveira, P.J.The principal mechanisms by which DBD plasma actuators influence flow characteristics, and are thus able to control that flow, depend strongly on their modes of actuation. Here two different modes based on steady and unsteady actuation are compared and investigated. A simple sinusoidal voltage distribution and a duty cycled sinusoidal voltage were considered for these purposes. Leading edge separation around a stalled NACA 0012 airfoil at Re=3 ×10^16 is considered as test case. A simplified phenomenological model which uses the correct scale of the plasma body force is considered for the modeling of the plasma actuator effects. The steady actuation results show that flow control can be effectively achieved by this mode of operation with continuous injection of momentum in the boundary layer. Unsteady actuation with an imposed frequency equal to the calculated natural frequencies of the flow gives rise to a resonance actuation effect.
- 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.
- Implementation of the classical plasma–fluid model for simulation of dielectric barrier discharge (DBD) actuators in OpenFOAMPublication . Abdollahzadehsangroudi, Mohammadmahdi; Páscoa, J.C.; Oliveira, P.J.To simulate the coupled plasma and fluid flow physics of dielectric-barrier discharge, a plasma–fluid model is utilized in conjunction with a compressible flow solver. The flow solver is responsible for determining the bulk flow kinetics of dominant neutral background species including mole fractions, gas temperature, pressure and velocity. The plasma solver determines the kinetics and energetics of the plasma species and accounts for finite rate chemistry. In order to achieve maximum reliability and best performance, we have utilized state-of-the-art numerical and theoretical approaches for the simulation of DBD plasma actuators. In this respect, to obtain a stable and accurate solution method, we tested and compared different existing numerical procedures, including operator-splitting algorithm, super-timestepping, and solution of the Poisson and transport equations in a semi-implicit manner. The implementation of the model is conducted in OpenFOAM. Four numerical test cases are considered in order to validate the solvers and to investigate the drawbacks/benefits of the solution approaches. The test problems include single DBD actuator driven by positive, negative and sinusoidal voltage waveforms, similar to the ones that could be found in literature. The accuracy of the results strongly depends to the choice of time step, grid size and discretization scheme. The results indicate that the super-time-stepping treatment improves the computational efficiency in comparison to explicit schemes. However, the semiimplicit treatment of the Poisson and transport equations showed better performance compared to the other tested approaches.
- 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.
- Numerical simulation of the polymer electrolyte membrane fuel cells with intermediate blocked interdigitated flow fieldsPublication . Bagherighajari, Fatemeh; Ramiar, Abbas; Abdollahzadehsangroudi, Mohammadmahdi; Pascoa, José; Oliveira, Paulo J.The main purpose of this paper is to study fuel cell performance using an interdigitated flow field with intermediate channel blocks on the cathode side. Application of an intermediate block in the middle of the interdigitated flow channel is a very new idea aimed at increasing the performance of polymer membrane fuel cells, which in practice result in novel arrangements of interdigitated flow channels. A middle block is desirable because the change in flow channel is minimal, the cost of fabricating bipolar plates does not increase, and it leads to an increase in the transfer rate of reactants into the gas diffusion layer due to enhanced over-rib flow pattern and direction. In this work, a three-dimensional, isothermal, and two-phase model is used to simulate the performance of such fuel cells. The polarization curves, the distribution of reactants on the cathode side, the distribution of liquid water, and the induced transverse flow were analyzed for three type of interdigitated flow fields along with parallel flow fields at reference conditions. The results showed that interdigitated flow fields with middle blocks lead to an increase in reactant transfer to the catalyst layer, an increase in reaction rate, and better removal of the resulting liquid water within the fuel cell. In the reference condition, in terms of maximum power density, the type I interdigitated flow field (without intermediate block) increased the net power by 8.2% compared to the parallel flow field, and the type II and III interdigitated flow fields also increased the power by 12.58% and 9.03%, respectively. At high current density, the type II interdigital flow field had the best performance in terms of enhancing the transfer of reactants to the catalyst layer and the expulsion of liquid water from that layer.
- Parametric optimization of surface dielectric barrier discharge actuators for ice sensing applicationPublication . Abdollahzadehsangroudi, Mohammadmahdi; Rodrigues, Frederico; Nunes-Pereira, João; Páscoa, J. C.; Pires, LuísIn this paper a parametric optimization of the dielectric barrier discharge (DBD) plasma actuator is con ducted in order to achieve better ice sensing and deicing performance. For this purpose, different DBD plasma actuators were tested by changing the main geometrical dimension of the DBD plasma actuator and dielectric material. Both the ice sensing and thermal characteristics of the DBD plasma actuator were analyzed and compared. The results reveal that there exists two separate set of optimum parameters that lead to best ice sensing and thermal behavior. For both the sensing and thermal characteristics, the thinnest DBD showed the best performance. Kapton DBD plasma actuator showed the highest surface temperature while PMMA (poly methyl methacrylate) had the best performance for ice sensing. In the end, the deicing performance of a DBD actuator that had in average better thermal and ice sensing performance was tested for deicing an ice layer and a frost layer. The progress of the deicing process and the ice sensing measure on the surface were recorded and analyzed.