Search

This study is focused on the flow physics in the condition of employing the active flow control methods and DBD plasma actuators as a transverse jet. In the current research, a single DBD plasma actuator is added to the Trailing Edge of a flat plate model and several wind tunnel experiments are conducted to study the flow structures. The salient goal of this work is to investigate the flow physics of Plasma Jet in Cross-Flow. Wind tunnel experiments results in two different free stream velocities of U ∞ = 10 m/s and U ∞ = 20 m/s and several model's angles of attack show that the flow domain consists of two different counter rotating vortices at S t = 0. 1886 and 0. 1725 and a secondary vortex with S t = 0. 5842. The manner of these vortices in the different A o A and free stream velocities, and also the shape of the velocity profile in the near wake and far-field wake of the plasma jet prove that the flow domain around the Plasma Jet in Cross-Flow is very similar to the flow around an airfoil equipped with Gurney Flap. [ABSTRACT FROM AUTHOR]

Cold 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. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the effectiveness of plasma actuators in controlling the flow around a finite wall-mounted square cylinder (FWMSC) with a longitudinal aspect ratio of 4. The test is conducted in a small-scale closed return-type wind tunnel. The Reynolds number of the experiments, Red, is 500 based on the width of the bluff body and the freestream velocity. The plasma actuators are installed on the top surface and the rear surface of the square cylinder. The induced flow velocities of the plasma actuators are modulated by adjusting the operating voltage and frequency of the high-voltage generator. In this work, particle image velocimetry (PIV) is used to obtain the velocity fields. Furthermore, force calculations are conducted to investigate the effect of using plasma actuators with different driving voltages on the drag force. Our results show that the plasma actuators can successfully suppress flow separation and reduce the turbulent kinetic energy (TKE) in the wake. A correlation between the drag coefficient and the operating voltage of the power generator is also revealed, and the mean drag coefficient is found to decrease with increasing imposing voltage. The plasma actuators can enhance the momentum exchange and the interactive behavior between the shear layer and the flow separation region, resulting in flow reattachment at the free end and shrinkage of the recirculation zone in the near-wake region of the bluff body. Overall, the present study demonstrates the practical effectiveness of using plasma actuators for flow control around FWMSC. [ABSTRACT FROM AUTHOR]

The pervasiveness of unmanned air vehicles (UAVs), from insect to airplane scales, combined with active flow control maturity, has set the scene for vehicles that differ markedly from present-day configurations. Nano and micro air vehicles, with characteristic Reynolds numbers typically less than 105, rely on periodically generated leading-edge vortices for lift generation, propulsion, and maneuvering. This is most commonly achieved by mechanical flapping or pulsed plasma actuation. On larger UAVs, with Reynolds numbers greater than 105, externally driven and autonomous fluidic systems continue to dominate. These include traditional circulation control techniques, autonomous synthetic jets, and discrete sweeping jets. Plasma actuators have also shown increased technological maturity. Energy efficiency is a major challenge, whether it be batteries and power electronics on nano and micro air vehicles or acceptably low compressor bleed on larger UAVs. Further challenges involve the development of aerodynamic models based on experiments or numerical simulations, as well as flight dynamics models. [ABSTRACT FROM AUTHOR]

In this paper, a multi-stage numerical methodology for the description of the Dielectric Barrier Discharge physics in air is discussed. The behavior of the heavy species is computed using drift-diffusion equations. Electrons are taken into account by solving a non-linear formulation of electrostatics. The physical effects of the steamer discharges are modelled by means of a simplified 0D approach. The model also includes a semi-implicit 0D model for the assessment of the elementary chemical processes occurring in air. The developed methodology is employed for the simulation of a volumetric Dielectric Barrier Discharge reactor. The obtained species number density and surface charge deposition rates and are shown and discussed. [ABSTRACT FROM AUTHOR]

• Separated flow is controlled by corona actuators operated in an original way. • The plasma discharge is created and stabilized by a new waveform instead of DC. • Separated flow of an airfoil at Reynolds 330 k in early stall is reattached. • Pulsed actuation for deep stall control is successfully tested. • The resulting flow control technique exhibits an interesting efficiency. In this experimental work, corona actuators with triangular tips on their anodes are applied on a symmetric airfoil and tested in the wind tunnel at a freestream velocity of 20 m/s (Re = 330k). The actuators are driven by a periodic waveform that improves remarkably their operability with respect to DC driving, increasing also their efficiency. The basic waveform or carrier wave can be modulated introducing a pulsed actuation as usually done for other kinds of plasma actuators. Steady (carrier only) and pulsed (modulated) operation are tested for two actuators, selected out of a larger set previously studied in the laboratory, and compared here with a standard wire-plate corona as reference. The diagnostics include measurements of aerodynamic forces, electrical parameters and local velocities, completed by surface visualizations. Force coefficients and electrical power are used to evaluate the actuators performance in terms of coefficients changes with respect to the smooth airfoil and to the unpowered case, determining also effectiveness parameters in N/W. At the same time, the control mechanism is studied by acquiring boundary layer velocity profiles with plasma off and on, and determining the momentum coefficient of the devices. The passive effects of the unpowered actuators are measured separately and also described by means of surface visualizations. The results confirm the streamwise momentum injection as main mechanism for these actuators, and lead to determine the best flow control achievable by this technique. [ABSTRACT FROM AUTHOR]

We address the problem of controlling the unsteady ow separation over an aerofoil, using plasma actuators. Despite the complexity of the dynamics of interest, we show how the problem of controlling ow separation can be formulated as a simple set-point tracking problem, so that a simple control strategy may be used. A robust output feedback control is designed, on the basis of a low-order, linear, dynamical model approximating the incompressible Navier-Stokes equations, obtained from the snapshots of 2D laminar finite element simulations at Re = 1; 000. Fast ow reattachment is achieved, along with both stabilisation and increase/reduction of the lift/drag, respectively. Accurate 2D finite element simulations of the full-order nonlinear equations illustrate the effectiveness of the proposed approach: good dynamic performances are obtained, as both the Reynolds number and the angle of attack are varied. The chosen output can be experimentally measured by appropriate sensors and, despite its simplicity, the proposed set-point tracking controller is suficient to suppress the laminar separation bubble; moreover, its extension to 3D turbulent configurations is straightforward ([33; 7]), thus illustrating the effectiveness of the designed control algorithm in more practical conditions, which are far from the design envelope. [ABSTRACT FROM AUTHOR]

Virtual control surfaces are assessed numerically as a means to enhance the aeroelastic response of a compressor cascade. Virtual surfaces are realized with plasma actuators placed on the pressure and on the suction side of the blade trailing edge. The plasma-induced flow is meant to be against the direction of the freestream. This allows for generating controlled recirculating flow areas and in turn modifying the effective blade camber and enlarging the actual chord. Computational fluid dynamic analyses with the blades at constant angle of attack show that the effects of pressure side actuation on flow field, pressure distribution and integral loads are comparable to those of flap-like devices. On the contrary suction side actuation yields effects which are analogous to those of wing spoilers. Traveling wave simulations for the torsion mode show that properly triggering an alternate pressure/suction side actuation during the blade pitching cycle improves significantly the blade aeroelastic stability. At the same time an effective reduction in the peaks of the oscillating airloads normal to the freestream direction is achieved, with potential benefits for the alleviation of fatigue phenomena. [ABSTRACT FROM AUTHOR]

Since the introduction of Suzen-Huang (SH) model in 2005, a huge number of publications discussing various aspects of this model has been reported. Most of these studies, till date are mainly focused on flow analyses in the framework of a Single Dielectric Barrier Discharge (SDBD) plasma actuator. This paper extends the application of the SH model to analyze the effects of some geometrical and electrical parameters of DBD plasma actuators in flow control applications. In some earlier experimental studies, it has been reported that a thick dielectric (a few mm) enhances the plasma extension resulting in an improvement of the electro-hydrodynamic (EHD) body force and the resulting ionic wind. Various parameters influence the electro-mechanical characteristics of DBD actuators such as - the dielectric thickness, the distance between both electrodes, the magnitude, the frequency and the waveform of the applied voltage The aim of this paper is to highlight the effects of these parameters on the ionic wind and EHD body force induced by the plasma discharge. It was observed that there is an optimal thickness of the dielectric layer for each configuration of actuator; above or below that optimal thickness, there is depreciation in the performance of the actuator. Thus, this paper summarizes the significance of the geometrical parameters for DBD plasma actuators. The optimal gap between the electrodes was found to be equal to zero which is in agreement with experimental observations. It is shown that with the increase in gap beyond 1 mm, the induced ionic wind velocity was significantly reduced. It is concluded that these two geometrical parameters play a fundamental role in optimization of the DBD actuator configurations. The applied voltage frequencies in the range from 1 to 4 kHz did not show significant performance variations in our DBD actuators configurations. Increasing the voltage amplitude leads to a better gain in terms of EHD force as reported in experimental studies. It is shown that square waveform of the applied voltage gives higher induced velocities compared to sinus or triangular waveform. [ABSTRACT FROM AUTHOR]

The influence of the air-exposed active electrode shape on the electrical, optical and mechanical behaviors of a surface DBD plasma actuator is investigated. For high voltage up to 24 kV, a first set of experiments highlights that the discharge current, the plasma morphology and the produced ionic wind are fully different, according to the active electrode shape. With a wire active electrode, the discharge is streamer-free, the ionic wind velocity is improved and more homogeneous along the active electrode compared to the typical baseline plate-to-plate surface DBD. On the contrary, with a sawtooth active electrode, the streamers are more intense and the velocity is higher in front of the tips and smaller between two successive tips, following the shape of the electrode edge. Finally, by increasing the high voltage up to 30 kV, maximum ionic velocities of 7.1 m/s and 8.65 m/s are reported, with a plate active electrode and a sawtooth one, respectively. To our knowledge, these are the highest ionic wind velocities that have never been measured with a single surface DBD based on two electrodes. [ABSTRACT FROM AUTHOR]

Plasma-controlled turbulent jets are investigated by means of Implicit Large–Eddy Simulations at a Reynolds number equal to 460,000 (based on the diameter of the jet and the centreline velocity at the nozzle exit). Eight Dielectric Barrier Discharge (DBD) plasma actuators located just before the nozzle exit are used as an active control device with the aim to enhance the mixing of the jet. Four control configurations are presented in this numerical study as well as a reference case with no control and a tripping case where a random forcing is used to destabilize the nozzle boundary layer. Visualisations of the different cases and time-averaged statistics for the different controlled cases are showing strong modifications of the vortex structures downstream of the nozzle exit, with a substantial reduction of the potential core, an increase of the jet radial expansion and an improvement of the mixing properties of the flow. [ABSTRACT FROM AUTHOR]

During the last twenty years DBD plasma actuators have been known by their ability for boundary layer flow control applications. However, their usefulness is not limited to this application field, they also present great utility for applications within the field of heat transfer, such as a way to improve the aerodynamic efficiency of film cooling of gas turbine blades, or de-icing and ice formation prevention. Nevertheless, there is a relative lack of information about DBD’s thermal characteristics and its heat generation mechanisms. This happens due to the extremely high electric fields in the plasma region and consequent impossibility of applying intrusive measurement techniques. Against this background, this work describes the physical mechanisms behind the generation of heat associated to the DBD plasma actuators operation. An experimental technique, based on calorimetric principles, was devised in order to quantify the heat energy generated during the plasma actuators operation. The influence of the dielectric thickness, as well as the dielectric material, were also evaluated during this work. The results were exposed and discussed with the purpose of a better understanding of the heat generation mechanisms behind the operation of DBD plasma actuators. [ABSTRACT FROM AUTHOR]

Direct Numerical Simulations in a turbulent channel flow at a moderate Reynolds number are performed in order to investigate the potential of Dielectric Barrier Discharge (DBD) plasma actuators for the reduction of the skin-friction drag. The idea is to use a sparse array of streamwise-aligned plasma actuators to produce near-wall spanwise-orientated jets in order to destroy the events which transport high-speed fluid towards the wall. It is shown that it is possible to reduce the drag by about 33.5% when the streamwise-aligned actuators are configured to generate appropriate spanwise-orientated jets very close to the wall so that the sweeps which are mainly responsible for the skin-friction are destroyed. We demonstrate that it is possible to achieve significant drag reduction with a sparse array of streamwise-aligned plasma actuators, with one order of magnitude less actuators than previous experiments in a similar set-up. [ABSTRACT FROM AUTHOR]

The goal of the present experimental study is to investigate the ability of a surface nanosecond pulsed dielectric barrier discharge plasma actuator, located at the leading edge of the airfoil, to delay flow separation along the suction side of an NACA0015 airfoil inclined at 13.5°, using a particle image velocimetry system. The free-stream velocity is equal to U0=40 m/s, giving a chord-based Reynolds number of Re c=1.33 \times 10^{6} . At such conditions, the baseline flow separation occurs at about 50% of chord. On the one hand, the results show that the separation location moves progressively toward the trailing edge when the high-voltage frequency F\mathrm {pulse} is increased, up to 85% of chord at 1630 Hz (reduced frequency F\mathrm {pulse}^{+} = 10.6 ), which is due to the increase of the injected electrical power with F\mathrm {pulse} (from 8 mW/cm at 40 Hz to 290 mW/cm at 1630 Hz). On the other hand, the use of a burst-modulated actuation (with a constant electrical power consumption equal to 145 mW/cm) does not produce the same behavior. At the lowest and highest frequencies (16 and 408 Hz, corresponding to the reduced frequencies of 0.1 and 2.65, respectively), the separation is delayed to about 60% of chord, while the most effective actuation is observed at F\mathrm {burst}= 80 Hz ( F\mathrm {burst}^{+}=0.53 ) with a separation delaying to 83% of chord. [ABSTRACT FROM AUTHOR]

Direct numerical simulations are used to probe the potential of plasma actuators to attenuate nonlinear steady crossflow vortices (CFVs). The investigated base flow mimics the three-dimensional boundary-layer flow of a swept wing. The plasma actuators are positioned at selected spanwise positions to weaken oncoming CFVs and thus the associated (secondary) instability. It is shown that both volume forcing against or in the direction of the crossflow (CF) can be effective, and a significant transition delay can be achieved. The spanwise position of the actuators should be such that the actuation-induced downdraft inhibits the CFV. The forcing in the direction of the CF does not reduce the mean CF, and an unfavourable spanwise position of the actuator may directly increase the strength of the CFV and eventually promote turbulence onset. The forcing against the CF never turned out to promote turbulence onset for all investigated positions, because of the favourable reduction of the mean CF. Adding then a second or third actuator downstream at appropriate spanwise positions can yield enhanced transition delay. [ABSTRACT FROM AUTHOR]

The current document describes a novel concept for actively isolating neighboring electrodes of multi-electrodes plasma actuators. For these actuators, such as the phased-array actuators (Corke and Matlis 2000) or the oscillating-wall ones (Choi et al. 2011), at different time instants, different sets of electrodes are operated; meanwhile the not-operated electrodes are floating grounds for the circuit. The proposed concept consists of splitting the amplitude of the voltage signals supplied to the operated electrodes and needed to generate the plasma discharge in a baseline signal and a time-modulated component. While the first is to be continuously supplied to all electrode sets and is of amplitude below the breakdown voltage for the considered fluid and plasma actuator, the latter, supplied only to the operated electrodes, has an amplitude such that, when superimposed to the baseline voltage, leads to the plasma discharge. The proposed operation reduces the voltage difference between operated and not-operated neighboring electrodes. Therefore, related detrimental interactions, such as parasitic discharges, are prevented. Two proof-of-concept experiments are performed and presented showing the proposed operation mode effective and efficient. [Display omitted] [ABSTRACT FROM AUTHOR]

Two dimensional numerical simulations of plasma actuator flow control of the ACHEON nozzle are conducted to give insight on the design of an experimental setup. Three configurations of the plasma actuators with single and multi AC-DBD actuators are used in steady mode of operation. AC-DBD actuators in standard mode (forward forcing mode), reverse mode (backward forcing mode) and plasma synthetic jets mode were used. Three different main groups of test cases were investigated by varying the reference velocity at the inlet of the nozzle stream from 4, 5 and 6 m/s. Moreover, each group includes four velocity ratios V R = 1 , 1.5 , 2 , 2.5 . The locations of the flow separation points are obtained numerically for all these cases and the plasma actuators are placed slightly upstream of these points leading to a system of seven DBD plasma actuators in the forward forcing mode over the Coanda surface. The induced thrust of the AC-DBD plasma actuators was estimated using a phenomenological model which considers the maximum achieved voltage and frequency from the experiments. Using an excitation voltage with maximum amplitude of 12 kVpp and frequency of 20 kHz, ionic wind was formed with 2.4 m/s velocity. The effects of plasma actuator are presented through change of the thrust and velocity angle and thrust vectoring efficiency. Preliminary results of the experimental set-up correlate well with the numerical design values. [ABSTRACT FROM AUTHOR]

The effects of plasma actuation in a flat plate boundary layer with zero pressure gradient have been simulated. Based on these simulations, non-dimensional parameters and a combined wall jet/boundary layer model of the velocity profile have been developed. A parametric study using local linear stability analysis has been performed to examine the hydrodynamic stability of the velocity profiles created through this model. Convective and absolute instability mechanisms are found to be important, some of which have not been previously documented. Neutral stability curves have been computed for the different instabilities, and when put in terms of the shape factor, they still compare favorably with reported canonical results, indicating that the critical Reynolds number is primarily a function of the shape factor. These results are also discussed in relation to existing experimental results as well as with respect to their implementation. [ABSTRACT FROM AUTHOR]

An exploratory numerical study of the control of transitional and turbulent separated flows by means of dielectric-barrier-discharge (DBD) actuators is presented. The flow fields are simulated employing a high-fidelity Navier-Stokes solver augmented with a phenomenological model representing the plasma-induced body forces imparted by the actuator on the fluid. Several applications are considered, including interaction of an actuator with a laminar boundary layer, suppression of wing stall, control of boundary layer transition on a plate, control of laminar separation over a ramp, and turbulent separation over a wall-mounted hump. Effective suppression of stall over a NACA 0015 airfoil at moderate Reynolds numbers is demonstrated using either co-flow or counter-flow actuators pulsed at a sufficiently high frequency. By contrast, continuous actuation is found to provide little control of separation. For a laminar boundary layer developing along a flat plate, a counter-flow DBD actuator is shown to provide an effective on-demand tripping device. This property is exploited for the suppression of laminar separation over a ramp. Control of turbulent boundary-layer separation over a wall-mounted hump suggests that once the flow is turbulent, control effectiveness is only achieved for higher actuator strengths with implications for the scalability of DBD devices to higher freestream velocities. [ABSTRACT FROM AUTHOR]

This paper presents the measurement of the magnetic field distribution and electronic thrust of atmospheric pressure glow discharge (APGD) plasma at flat panel. The characteristics of APGD plasma and its some mechanism problems have been investigated from a new point of view. The distribution of the magnetic intensity around the APGD low-temperature plasma and its electronic thrust were measured respectively. The results show that the directional airflow induced by APGD plasma is related to the distribution of the magnetic field, and the electronic thrust of APGD plasma is influenced by the structure of the APGD plasma actuators. The experimental study is significant for the further study about the characteristics of APGD low-temperature plasma. [ABSTRACT FROM AUTHOR]

Abstract: In this study a new computational model is proposed to simulate the flow control effects of glow discharge plasma. A velocity inlet boundary condition is applied to model the plasma induced velocity. A test case of the viscous flow around a two-dimensional circular cylinder is used to validate the model. A good agreement is made between the numerical and experimental results. [Copyright &y& Elsevier]

Abstract: In recent years electroaerodynamic actuators have been rather intensively studied in order to control airflow [H. Velkoff, R. Godfrey, J. of Heat Transfer 101 (1979) 157; S. El-Khabiry, G.M. Colver, Phys. Fluids 9 3 (1997) 587; A. Soldati, S. Banerjee, Phys. Fluids 10 (1998) 1742; R. Vilela Mendes, J.A. Dente, J. Fluids Eng. 120 (1998) 626; A. Schütze, et al., IEEE Trans. Plasma Sci. 26 6 (1998) 1685; G.M. Colver, S. El-Khabiry, IEEE Trans. Ind. Appl. 35 2 (1999) 387; J.R. Roth, D.M. Sherman, S.P. Wilkinson, AIAA J. 38 7 (2000) 1172; L. Léger, E. Moreau, G. Artana, G. Touchard, J. Electrost. 50-51 (2001) 300 ; W. Shy, B. Jayaraman, A. Andersson, J. Appl. Phys. 92 11 (2002) 6434; G. Artana, J. D''Adamo, L. Léger, E. Moreau, G. Touchard, AIAA J. 40 9 (2002) 1773; J.R. Roth, Phys. plasmas 10 5 (2003) 2117; K.T. Hyun, C.H. Chun, Exp. Fluids 35 (2003) 541; G. Artana, R. Sosa, E. Moreau, G. Touchard, Exp. in Fluids 35 (2003) 580; C.L. Enloe, T.E. McLaughlin, R.D. VanDyken, K.D. Kachner, E.J. Jumper, T.C. Corke, AIAA J. 42 3 (2004) 589; C.L. Enloe, T.E. McLaughlin, R.D. VanDyken, K.D. Kachner, E.J. Jumper, T.C. Corke, M. Post, O. Haddad, AIAA J. 42 3 (2004) 595; M. Samimy, I. Adamovich, B. Webb, J. Kastner, J. Hileman, S. Keshav, P. Palm, Exp. Fluids 37 (2004) 577; J.P. Boeuf, L.C. Pitchford, J. Appl. Phys. 97 (2005); E. Moreau, A. Labergue, G. Touchard, J. Adv. Oxydation 8 2 (2005) 241; M. Forte, L. Léger, J. Pons, E. Moreau, G. Touchard, J. Electrost. 63 (2005) 929; J. Pons, E. Moreau, G. Touchard, J. Phys., D, Appl. Phys. 38 (2005) 3635; E. Moreau, C. Louste, G. Touchard, J. Electrost. 66 (2008) 107 ; G.I. Font, AIAA Journal 44 7 (2006) 1572; Y. Sung, W. Kim, M.G. Mungal, M.A. Cappeli, Exp. Fluids 41 (2006) 479; E. Moreau, L. Léger, G. Touchard, J. Electrost. 64 (2006) 215; R. Sosa, G. Artana, J. Electrost. 64 (2006) 604 ]. Their principle is to produce a plasma in which ions are submitted to electric field. Then, the molecules of air are drifted by ions, generating an “electric wind”. In the LEA (Laboratoire d''Etudes Aérodynamiques), three kinds of actuators have been mainly performed and studied: the DC actuator, the DBD actuator and the sliding discharge actuator. In the present paper we will first examine briefly the setup of each kind of actuators and how they produce electric wind. Then we will describe a new kind of device based on two DBD actuators and performed to generate a micro-jet in an adjustable direction. [Copyright &y& Elsevier]

Abstract: The introduction of an electro-hydrodynamic (EHD) force in high performance numerical simulation may pose some problems as a consequence of the large differences between time or spatial scales of the physics of the discharge and those of interest for the fluid flow description. In this paper, we try to simplify this problem by looking for a correspondence between the global flow modifications produced by an EHD actuation and those by a moving body surface. Direct numerical simulations (DNS) of flow past a rotating cylinder are performed. For a flow regime corresponding to Reynolds number based on the cylinder diameter and free-stream velocity of the flow of 125 (wake-transition regime), the simulations allow us to make a comparison with particle image velocimetry (PIV) measures of the flow induced by a dielectric barrier discharge (DBD) plasma actuator suitably disposed on the cylinder surface. The results obtained from the projection of mean velocity fields show that the time-averaged vortical structures in the two cases enable us to establish a good analogy between actuations produced by both mechanisms. [Copyright &y& Elsevier]

The effect of high-frequency dielectric barrier discharge plasma actuators on the noise of a flow around a circular cylinder is experimentally studied. It is shown that the plasma actuators are able to reduce the vortex noise of a cylinder within the range of velocities typical for aeroacoustic applications. [ABSTRACT FROM AUTHOR]

This paper examines the possibility of controlling jet-wing interaction noise by plasma actuators. The low-frequency part of the jet installation noise is considered as produced by the diffraction of instability wave packets developing in the jet shear layer. Thus, the main idea of noise control comes to the attempt to reduce the amplitude of these wave packets near the wing trailing edge. A simplified jet-plate configuration is studied experimentally for jet Mach numbers ranging from 0.4 to 0.6. To avoid additional complications related to the control of stochastic signals in the first step, the jet is excited by a loudspeaker at a frequency corresponding to Strouhal number 0.6. Acoustic forcing generates axisymmetric instability wave in the jet shear layer, which is the object of control. The control action is implemented by a high-frequency dielectric barrier discharge (HF DBD) plasma actuator with a ring-like electrode mounted inside the nozzle near the exit. It is demonstrated that installation noise can be significantly suppressed if the plasma actuator generates instability wave with the amplitude equal to that of the excited by the loudspeaker, but in antiphase to it, and vice versa, if these instability waves are in phase, installation noise increases by about 6 dB. The obtained results support the idea that low-frequency jet-wing installation noise can be controlled in a linear framework. [ABSTRACT FROM AUTHOR]

Sliding plasma actuators were used to control the flow-induced broadband noise radiating from a bluff body. The structure consisted of a cylinder and a torque link that was installed on the lee side of the cylinder. The objective was to reduce the noise generated during the cylinder wake impinging on the torque link. By manipulating cylinder wake with the externally-imposed body force generated by the plasma actuators, the flow-structure interaction was reduced, leading to an attenuation of the broadband noise up to 3 dB in overall sound pressure level at a free stream speed of 30 m/s. [ABSTRACT FROM AUTHOR]

A dielectric barrier discharge actuator (DBD) is considered and studied as a stall recovery device. The DBD is installed on the nose of a NACA0015 airfoil with chord × span 300 × 930 mm. The geometry of the exposed electrode has periodic triangular tips purposely designed for the case under study. Wind tunnel tests have been carried out over a range of airspeeds up to 35 m/s with a Reynolds number of 700 k. The flow morphology has been characterized by means of the particle image velocimetry technique, obtaining velocity fields and pressure coefficients. By exploring different planes along the model span, the three-dimensional effect of the DBD has been reconstructed, identifying the flow region mainly sensitive to the plasma actuation. Finally, the actuator effectiveness has been quantified accounting for the power consumption data, leading to defining further design improvements in view of a better efficiency. [ABSTRACT FROM AUTHOR]

The flow control effects of a nanosecond-pulse-driven dielectric barrier discharge plasma actuator (ns-DBDPA) in dynamic stall flow were experimentally investigated. The ns-DBDPA was installed on the leading edge of an airfoil model designed in the form of a helicopter blade. The model was oscillated periodically around 25% of the chord length. Aerodynamic coefficients were calculated using the pressure distribution, which was obtained by the measurement of the unsteady pressure by sensors inside the model. The flow control effect and its sensitivity to pitching oscillation and ns-DBDPA control parameters are discussed using the aerodynamic coefficients. The freestream velocity, the mean of the angle of attack, and the reduced frequency were employed as the oscillation parameters. Moreover, the nondimensional frequency of the pulse voltage, the peak pulse voltage, and the type and position of the ns-DBDPA were adopted as the control parameters. The result shows that the ns-DBDPA can decrease the hysteresis of the aerodynamic coefficients and a flow control effect is obtained in all cases. The flow control effect can be maximized by adopting the low nondimensional frequency of the pulse voltage. [ABSTRACT FROM AUTHOR]

We propose the use of plasma actuators in order to control the vortex induced vibration phenomena (VIV) originated by an airflow around a rigid circular cylinder. The body was placed in a closed loop wind tunnel and mounted on elastic supports that allowed small oscillatory movements in the transverse direction with respect to the free stream. Our goal was to suppress the vibrations that naturally occurred in this configuration. To this end, two plasma actuators were disposed symmetrically on the surface of the cylinder along the span that transferred momentum to the fluid by means of a dielectric barrier discharge. The experiments were performed by varying the free stream velocity and the actuation parameters, which means voltage and frequency were kept constant throughout our experiments. We characterised the dynamics of the system for experimental conditions by involving a high reduced mass m ∗ ≈ O (103) and by considering a range of Reynolds numbers regarding the intermediate sub critical flow regime 1000 ≲ Re ≲ 10000. The reduced velocities lied within the range of 4.50 < U r < 6.25. Our results show that the plasma actuators exhibit a large ability to suppress the VIV throughout the whole range of the experimental conditions tested. Complementary measurements undertaken with a particle image velocimetry (PIV) system enabled us to explain the outstanding performance observed. [ABSTRACT FROM AUTHOR]