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Author: Karthik Naganathan
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Category :
Languages : en
Pages : 0
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Plasma actuators are active flow control devices used for vortex generation, momentum addition, and boundary layer attachment. The advantages of plasma actuators are that they are lightweight, quick to respond, and lack moving parts. Channel Dielectric Barrier Discharge actuators are a type of dielectric barrier discharge actuators in which the exposed electrode is placed in the bulk fluid to reduce viscosity effects. There are very few models that can predict the plasma forcing with good accuracy. These models however do not account for the geometric parameters such as the width of the electrode. This thesis discusses two numerical models, one built from a surface DBD model and one built from electrostatic modeling. The modified surface DBD model predicts exit velocity profiles similar to the experimental results. But it fails to account for some geometric parameters. The electrostatic model successfully captures the potential distribution asymmetry. The forcing function obtained by curve fitting the force distribution was adjusted to give reasonable velocity distribution when implemented as a source term in the CFD solver. The adjusted ES model predicted velocity contours and Reynolds number variation with good accuracy.
Author: Karthik Naganathan
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Plasma actuators are active flow control devices used for vortex generation, momentum addition, and boundary layer attachment. The advantages of plasma actuators are that they are lightweight, quick to respond, and lack moving parts. Channel Dielectric Barrier Discharge actuators are a type of dielectric barrier discharge actuators in which the exposed electrode is placed in the bulk fluid to reduce viscosity effects. There are very few models that can predict the plasma forcing with good accuracy. These models however do not account for the geometric parameters such as the width of the electrode. This thesis discusses two numerical models, one built from a surface DBD model and one built from electrostatic modeling. The modified surface DBD model predicts exit velocity profiles similar to the experimental results. But it fails to account for some geometric parameters. The electrostatic model successfully captures the potential distribution asymmetry. The forcing function obtained by curve fitting the force distribution was adjusted to give reasonable velocity distribution when implemented as a source term in the CFD solver. The adjusted ES model predicted velocity contours and Reynolds number variation with good accuracy.
Author: Dana Elam
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Category :
Languages : en
Pages :
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Turbulent skin-friction control is the subject of much research and the use of transverse (spanwise) oscillating motions offers the means of obtaining a significant reduction in skin-friction. Dielectric barrier discharge (DBD) actuators can be used to generate spanwise oscillating waves but the difficulty in placing a sensor in the area of plasma gives rise to problems in recording near-wall velocities. A modified version of the Shyy et al. (2002) DBD model was integrated into a direct numerical simulation (DNS). This numerical model was used in a series of two-dimensional simulations, in initially quiescent ow, and the results were compared to results reported from experimental investigations. A close affinity was found confirming that the DBD model is satisfactory. Both a temporal and a spatial, spanwise oscillating ow were investigated. Only one plasma profile was investigated. Three actuator spacings were investigated. Only the largest actuator spacing resulted in a gap between each plasma profile that was larger than the plasma profile width itself. A spatially uniform plasma configuration produced larger DR% than spanwise wall oscillation for both spatial and temporal waves, maximum DR = 51% compared to a DR = 47% for a spanwise wall oscillation. Increased skin-friction reductions originated from the displacement of the Stokes layer. The spatial wave produced lower skin-friction values than temporal waves for all the configurations. For both spatial and temporal waves the performance of the discrete configurations in producing an overall skin-friction reduction decreased with increasing actuator spacing. Using both temporal and spatial waves, the configuration with the largest spacing, which is relatively small, did not produce a drag reduction for any case that was tested.
Author: Kendal David Dennis
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ISBN:
Category : Boundary layer control
Languages : en
Pages : 162
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Author: Rocco Arpa
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Category :
Languages : en
Pages :
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Author: Alexandre Likhanskii
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Category :
Languages : en
Pages : 182
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Author: Denis Palmeiro
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ISBN: 9780494823682
Category :
Languages : en
Pages : 198
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Book Description
Single-dielectric-barrier-discharge (SDBD) plasma actuators have shown much promise as an actuator for active flow control. Proper design and optimization of plasma actuators requires a model capable of accurately predicting the induced flow for a range of geometrical and excitation parameters. A number of models have been proposed in the literature, but have primarily been developed in isolation on independent geometries, frequencies and voltages. This study presents a comparison of four popular plasma actuator models over a range of actuation parameters for three different actuator geometries typical of actuators used in the literature. The results show that the hybrid model of Lemire & Vo (2011) is the only model capable of predicting the appropriate trends of the induced velocity for different geometries. Additionally, several modifications of this model have been integrated into a new proposed model for the plasma actuator, introducing a number of improvements.
Author: Régis Sperotto de Quadros
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ISBN:
Category :
Languages : en
Pages : 208
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Author: Kazuo Shimizu
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Category : Technology
Languages : en
Pages :
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Dielectric barrier discharge (DBD) plasma actuators are a technology which could replace conventional actuators due to their simple construction, lack of moving parts, and fast response. This type of actuator modifies the airflow due to electrohydrodynamic (EHD) force. The EHD phenomenon occurs due to the momentum transfer from charged species accelerated by an electric field to neutral molecules by collision. This chapter presents a study carried out to investigate experimentally and by numerical simulations a micro-scale plasma actuator. A microplasma requires a low discharge voltage to generate about 1 kV at atmospheric pressure. A multi-electrode microplasma actuator was used which allowed the electrodes to be energized at different potentials or waveforms, thus changing the direction of the flow. The modification of the flow at various time intervals was tracked by a high-speed camera. The numerical simulation was carried out using the Suzen-Huang model and the Navier-Stokes equations.
Author:
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Category :
Languages : en
Pages : 84
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Dielectric Barrier Discharge (DBD) type devices, when used as plasma actuators, have shown significant promise for use in many aeronautical applications. Experimentally, DBD actuator devices have been shown to induce motion in initially still air, and to cause re-attachment of air flow over a wing surface at a high angle of attack. This thesis explores the numerical simulation of the DBD device in both a lD and 2D environment. Using well established fluid equation techniques, along with the appropriate approximations for the regime under which these devices will be operating, computational results for various conditions and geometries are explored. In order to validate the code, results are compared to analytic or experimental data whenever possible, or matched with other similar numeric simulations to help establish the accuracy of the code. Solutions to Poisson's equation for the potential, electron and ion continuity equations, and the electron energy equation are solved semi-implicitly in a sequential manner. Each of the governing equations is solved by casting them into a tridiagonal grid, and using the computationally efficient Thomas algorithm to solve lD regions in a single iteration. The Scharfetter-Gummel flux discretization method is used to add stability to the code when transitioning from a field to diffusion dominated region or vice versa. Estimates for the ionization and recombination rates and for the transport coefficients of the background gas are calculated as a function of the local average electron energy, and updated for every calculation point in the domain on the completion of the solution to the electron energy equation.
Author: Farid Mirhosseini
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ISBN:
Category : Actuators
Languages : en
Pages : 0
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"Plasma actuators for aerodynamic applications are receiving significant research attention and it is necessary to know the effects of this plasma on the vehicle radar cross section (RCS). This study identifies the critical parameters affecting the RCS of plasma along with experimental techniques and numerical techniques for determining the effects of plasma on RCS. A review of plasma physics is presented along with the background of cavity design, cavity-waveguide coupling, choke design and the microwave perturbation technique. A cylindrical dielectric barrier discharge (DBD) plasma under five different pressures is generated in an evacuated glass tube. The microwave perturbation method is used to measure permittivity and loss factor of the plasma and then the plasma frequency, electron-neutral collision rate and electron density are determined for these five pressures. Simulations by a commercial microwave simulator are comparable to the experimental results which show little effect at sea level and increasing effects with increased elevation. Plasma has a capability that its refractive index can be controlled by changing parameters such as the electron density profile, plasma frequency or collision rate so the RCS becomes controllable. However controlling the aforementioned parameters practically in order to decrease RCS is not as simple as the theoretical simulations. From the various methods of plasma generation, our focus is on the DBD because this method has shown benefits like aerodynamic drag reduction noticed in the last decade. The effect of a plasma slab on the RCS of a conductive sheet is investigated. The RCS is simulated and measured to verify the validity of the model used for simulations. Moreover, we show the DBD actuator generates extra scattering because of Bragg diffraction phenomenon not previously reported in the DBD literature. A comprehensive study on dispersive media RCS using Finite-Difference Time-Domain (FDTD) method is done. The method used to generate the plane wave is the discrete plane wave (DPW) method. However, by plane wave we mean a wave packet which can behave like a plane wave not a real plane wave. A 12-layer split-field perfectly matched layer (PML) is used for the Absorbing Boundary Conditions (ABC). The dispersive media is modelled by shift-operator FDTD. Near-to-Far Field transformation (NTFT) is applied to calculate RCS in the far-field. This NTFT method is based on the surface equivalence theorem (Huygens’s principle). Finally the Fast Fourier Transform (FFT) is used to transform time domain signals to the frequency domain. Moreover, the simulation was extended for anisotropic dispersive media for two general profiles of exponential and polynomial. The results show that by choosing the right profile the RCS can be reduced to a large extent; however, achieving such a profile practically is very challenging."--Pages ii-iii.
