Active Control of Flow and Turbomachinery Ref.

To request a copy of a publication send an email to antonio.ficarella02@gmail.com

2017

"ACTIVE SENSORS/ACTUATORS‐BASED FLOW AND NOISE CONTROL FOR AEROSPACE APPLICATIONS", Maria Grazia De Giorgi, Elisa Pescini, Antonio Suma, Maria A. Signore, Chiara De Pascali, Antonio Ficarella,  XIX AISEM 2017, Lecce, 21 ‐ 23 Febbraio 2017

Several active and passive flow control systems are studied to improve the performances of fluid machineries and to increase aerodynamic efficiency of propulsion systems. Among all the well-known active flow control devices, the dielectric barrier discharge plasma actuator (PA) is in full expansion and of great interest in the scientific community. A PA modifies the following behaviour of a fluid by providing an electronically controllable disturbance that brings to drag reduction, flow separation control, enhanced mixing, and noise suppression. PA is potentially easy to construct, has no moving parts and has low power requirements. This leads to its possible applications for separation control in low pressure turbine blade and compressor cascade, tip clearance flow control and compressor stability range extension. The present work reports the design and fabrication of cheap Kapton-based flow turbulence capacitive sensors able to be embedded into aircraft wing profiles and airfoil structures for critical turbulence conditions detection and early-detected separated flows control. The embedded system will provide a Kapton-foil based pressure detection and linear/synthetic jet plasma actuators working in feedback, for prevention and active reduction of separated flow for regional aircraft applications.

"Micro DBD plasma actuators for flow separation control on a low pressure turbine at high altitude flight operating conditions of aircraft engines", De Giorgi, M.G., Ficarella, A., Marra, F., Pescini, E., Applied Thermal Engineering, Vol. 114, pp. 511-522,  10.1016/j.applthermaleng.2016.11.198, 2017.

The present study aims to investigate, by numerical simulations, the potentiality of alternate current (AC) driven plasma actuators to reattach the separated flow along a low pressure turbine blade operating at low-Reynolds number. The flow over a curved wall plate, installed in a wind tunnel, to simulate the suction surface of a low-pressure turbine blade, was examined. Different plasma actuator geometries have been studied: a macro single dielectric barrier discharge (SDBD), a micro SDBD and a micro linear plasma synthetic jet (L-PSJ) without and with thrust vectoring. Numerical simulations were performed in absence and in presence of actuation. In presence of actuation, the plasma induced force was modelled and introduced as a source term in the momentum Navier-Stokes equation. The numerical flow simulations were validated with the experimental data. To compare the different plasma actuator geometries effects, the velocity profiles have been considered. The micro SDBD and the micro L-PSJ with thrust vectoring led to a reduction of recirculation and a substantial decrease of the boundary layer thickness. The reattachment of the flow was also evident by analyzing the wall shear stress profiles and the vortical flow structure using the Q-criterion. The characteristics of the boundary layer (shape factor, displacement and momentum thickness) in presence of the different actuation techniques were also studied.

"Investigation of the boundary layer characteristics for assessing the DBD plasma actuator control of the separated flow at low Reynolds numbers", Pescini, E., Marra, F., De Giorgi, M.G., Francioso, L., Ficarella, A., Experimental Thermal and Fluid Science, Vol. 81, pp. 482-498, 10.1016/j.expthermflusci.2016.09.005, 2017. 

The present study intends to investigate the boundary layer characteristics to assess the potentiality of the single dielectric barrier discharge plasma actuators (SDBDPAs) to reattach the separated flow at low Reynolds numbers. The effect of the actuator geometrical parameters and of the Reynolds number on the device control authority was experimentally investigated. For this aim, a curved wall plate, which profile shape was designed to reproduce the suction surface of a low-pressure turbine (LPT) blade, was installed in the test section of a closed loop wind tunnel and a groove was made over it, at the front of the adverse pressure gradient region, for allocating a SDBDPA. Three actuators, characterized by different streamwise width, were manufactured by photolithography technique and they were tested. The velocity flow field, in both presence and absence of external flow, was investigated by particle image velocimetry (PIV) measurements. When the actuator was turned on, a sinusoidal voltage excitation with amplitude of 8 kV and frequency of 2 kHz was applied and the dissipated power (View the MathML source) was retrieved by electrical characterization. The effect of the active flow control was firstly estimated by analyzing the plasma induced velocity fields in absence of external flow. Subsequently the wind tunnel inlet free stream velocity (View the MathML source) was set to 1.54 m/s. The velocity, turbulence intensity (Tu) and vorticity (ωz  ) fields together with the boundary layer shape factor (H12) and momentum coefficient (cμ) were evaluated in both presence and absence of actuation. All the aforementioned analyses together with the estimation of the device electrical-to-fluidic energy conversion efficiency (ηfm  ) allowed identifying the best actuator geometry. Then, that configuration was chosen to investigate the effects of the wind tunnel velocity on the device control authority. The tested View the MathML source values ranged from 1.54 m/s up to 3.16 m/s. In absence of actuation, a large reverse flow and high turbulence intensity was observed in the separation region. Considering the actuated cases, it was found that at View the MathML source ≈ 7 W, the SDBDPA operation always implied a reduction of the separated region, of the flow angle and of the turbulence intensity. Moreover, the plasma induced jet had a larger impact on the flow at lower velocities and a low flow control effect was noticed at the highest View the MathML source values. The H12 factor evaluation confirmed the flow regimes at the different tested velocities (i.e. cμ values). The whole data set allowed to evaluate the actuator success for separation control and to identify a threshold value of the cμ coefficient delimiting the still detached flow from the reattached one.

2016

“Electrode Material Degradation Monitoring for Durable Dielectric Barrier Discharge Plasma Actuators Manufacturing”, Elisa Pescini, Maria Grazia De Giorgi, Luca Francioso, Antonietta Taurino, M. C. Martucci, Philippe Lavoie, AIAA SciTech, 54th AIAA Aerospace Sciences Meeting, 4‐8 January 2016, San Diego, California, USA, Paper N°. AIAA 2016‐0196, eISBN: 978‐1‐62410‐393‐3, doi: 10.2514/MASM16

This study aims to develop effcient, reproducible and durable plasma actuators. Thin metal deposition and high manufacturing reliability control were gained by adopting the photographic technique. As dielectric material degradation and electrodes corrosion are significant issues, emphasis was put in selecting materials that could withstand the plasma environment. Gold was selected as electrode material for all the geometric configurations. A Schott alkali-free borosilicate glass substrate was chosen as dielectric because of its resis- tance to material degradation in the plasma environment. Measurements of the actuator power consumption and capacitance were used to quantify the change in actuator performance over time. Moreover, scanning electron microscope images and energy dispersive X-ray spectroscopy analysis were utilized on the used devices to help explain the observed changes in actuator performance. After usage, unexpected degradation effects were observed on the gold electrodes, in both the front side and back side of each actuator. The electrode edges retracted and residual gold remained on the glass substrate. In particular, the exposed electrode width reduced by up to approximately 50%, depending on the actuator working conditions. Moreover, the morphology of the electrode surfaces changed and melting/crystalline reorganization of the gold layer was observed at the borders of the shrunk electrodes. As a consequence, a decrease of the actuator cold capacitance with age was evident. Furthermore, a rise in the actuator power consumption and effective capacitance was noted with increasing actuation time. At the same time, the actuator aging process produced an increase in its effective capacitance at a given dissipated power.

“Experimental and Numerical Study of Plasma Based Flow Control for Low Pressure Gas Turbines Operating at Low Reynolds Numbers”, E. Pescini, D. S. Martinez, M. G. De Giorgi, Antonio Ficarella, 6th EASN International Conference on Innovation in European Aeronautics Research, Porto, Portugal, 18-21 October 2016. 

High altitude cruise represents a crucial issue for small size low pressure turbines (LPT), commonly used in the propulsion of unmanned air vehicles (UAVs). The Reynolds number can drop below 25000, which in turn can lead to laminar boundary layer separation on the suction surface of the blades. This makes the turbine working in off-design conditions with very poor performances. Modifying the blade shape to counteract the boundary layer separation is not a feasible solution since the performance of the turbine will be adversely affected at the engine design conditions (take-off and landing). Therefore, the implementation of a boundary layer control system on the suction side of the turbine able to operate only at low Reynolds number is the most practical solution. The present study investigates experimentally and numerically the potential of an alternate current (AC) driven Single Dielectric Barrier Discharge Plasma Actuator (AC-SDBDPA) to reattach the separated flow at a Reynolds number around 2·104. The SDBDPA was designed and manufactured by means of lithographic technique, which ensured a thin metal deposition with high manufacturing reliability control. The experimental approach comprised the actuator testing over a curved plate with a shape designed to reproduce the suction surface of a LPT. A closed loop wind tunnel was employed. The curved plate was mounted directly over the bottom wall of the test section. The AC-SDBDPA was placed in a grove made at the middle of the curved plate and located at the front side of the adverse pressure gradient region. Sinusoidal voltage excitation was tested. The flow measurements –with and without actuation– were carried out by laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). Planar measurements were performed over the curved plate at the midspan plane. Simultaneously to the velocity measurements the applied voltage and the discharge current were acquired in order to determine the device dissipated power. The experimental data was complemented with CFD simulations based on the finite volume method. The actuator effect was modelled as a time-constant body force calculated prior to the fluid flow simulation by using a dual potential algebraic model. Reynolds Averaged Navier Stokes (RANS) method was used to consider the turbulence effect. The validity of the numerical model allows to expand the study of the actuation effect including different locations and multiple devices, saving considerably experimental efforts.

"INVESTIGATIONS OF THE ACTUATION EFFECT OF A SINGLE DBD PLASMA ACTUATOR FOR FLOW SEPARATION CONTROL UNDER SIMULATED LOWPRESSURE TURBINE BLADE CONDITIONS", Elisa Pescini, Fedele Marra, Maria Grazia De Giorgi, Luca Francioso, Antonio Ficarella, GT2016 - 57432, Proceedings of ASME Turbo Expo 2016: Turbine Technical Conference and Exposition, GT2016, June 13-17, 2016, Seoul, South Korea, 2016.

The present study intends to investigate the potentiality of the single dielectric barrier discharge plasma actuators (SDBDPAs) to reattach the separated flow, occurring at low Reynolds numbers. For this aim, a curved wall plate, which profile shape was designed to reproduce the suction surface of a low-pressure turbine (LPT) blade, was installed in the test section of a closed loop wind tunnel and a SDBDPA was placed in a groove made over it, at the front of the adverse pressure gradient region. The flow behavior in absence of actuation has been experimentally investigated by particle image velocimetry (PIV) and laser Doppler velocimetry measurements (LDV). Moreover, sinusoidal voltage excitation with amplitude of 8 kV and frequency of 2 kHz was applied to the SDBDPA and PIV measurements were also performed in presence of actuation. The applied voltage and the discharge current have also been recorded simultaneously, and they have been used for the determination of the device dissipated power. Different wind tunnel free stream velocities were investigated, both in absence and presence of actuation. The effect of the active flow control was then studied in the entire measurement domain by analyzing the velocity fields, the turbulence intensity (Tu) values, the momentum coefficient (cμ) and the boundary layer shape factor (H12). In absence of actuation, a large reverse flow and a turbulence intensity up to ≈60% was observed in the separation region. Good agreement was found between the flow results obtained by the two velocity measurement techniques. Considering the actuated cases, it was found that, in all the tested operating conditions, actuation implied a reduction of the separated region and the turbulence intensity, even if a low flow control effect was noticed at the highest tested velocity.

"Plasma actuator scaling down to improve its energy conversion efficiency for active flow control in modern turbojet engines compressors", De Giorgi M.G., Pescini E., Marra F., Ficarella A., Applied Thermal Engineering, vol. 106, pag. 334-350,  10.1016/j.applthermaleng.2016.05.186, 2016.

The present work was performed to investigate the employment of micro dielectric barrier discharge plasma actuators for mitigating separation, thereby decreasing wake losses and increasing efficiency, on a highly loaded compressor cascade. To this aim, the experimental characterization of the control device was initially done. A dedicated activity was devoted to microelectronic technology adoption for micro plasma actuator fabrication, together with batch production of electrodes with photolithographic techniques. The actuation effect on quiescent flow was evaluated by measuring the induced wall-jet with particle image velocimetry. The actuator power consumption was estimated by recording the applied voltages and resulting currents. Experimental results were then used to calibrate a multi-physics numerical model, for the prediction of the body forces induced by plasma actuator. Different algebraic models were compared. Numerical modelling was applied to predict the capability of micro plasma actuation to suppress flow separation into a highly-loaded subsonic compressor stator cascade. At first, simulations of the compressor cascade without active flow control were carried out and the results were compared with the literature experimental data. A good agreement was found between the experimental and the numerical results. Active flow control by the micro plasma actuator was then tested under different sinusoidal voltage amplitudes. It was found that the compressor pressure losses were reduced by increasing the applied voltage; actuation brought to a reduction in the pressure loss coefficient up to 14% and to an increase in static pressure up to 3%. When the actuator was on, the isosurface of the Q-criteria showed the reduction of secondary flow structures and the shape factor at the trailing edge of the midspan section was always lower than 2.2, confirming a reattachment of the flow. Furthermore, a conventional macro actuator found in the literature was also modelled and its actuation effect was compared to the one of the micro plasma actuator. In conclusion, the analysis of the actuation cost underlined that the adoption of micro actuation allowed reaching a higher gain when operating at lower voltage and same frequency.

"Flow separation control on a compressor-stator cascade using plasma actuators and synthetic and continuous jets", Traficante S., De Giorgi M.G., Ficarella A., Journal of Aerospace Engineering, vol. 29 n. 3, 10.1061/(ASCE)AS.1943-5525.0000539, 2016.

The effects of active separation control on a highly loaded subsonic compressor stator cascade were numerically studied by comparing the behavior of different devices: continuous jet actuator (CJA), zero-net mass-flux synthetic jet actuator (SJA), and plasma actuator (PA). For the jet actuator modeling, a suction/blowing type boundary condition was used, imposing a time-constant velocity for the CJA case and a prescribed sinusoidal time-varying velocity for the SJA case. For the PA case, the body force, which represents the effect of the plasma actuator on the flow, was added to the momentum equations in the computational fluid dynamics (CFD) code. The PA is slightly more efficient for the reduction of flow separation in the region just downstream of the blade actuators. However, at the same mechanical power delivered by the actuator to the fluid, the SJAs are more advantageous than the CJAs and slightly outperform plasma actuator application from the pressure loss reduction and pressure rise viewpoints. The fluidic jets have low power requirements, whereas the power consumption would be prohibitive for the PA configuration that shows low fluid mechanic efficiency. 

2015

"INVESTIGATION OF PLASMA ACTUATORS FOR FLOW SEPARATION CONTROL ON A LOW PRESSURE TURBINE BLADE AT LOW REYNOLDS NUMBER", Maria Grazia De Giorgi, Elisa Pescini, Fedele Marra, Antonio Ficarella, Luca Francioso, 23rd Conference of the Italian Association of Aeronautics and Astronautics, AIDAA2015, Politecnico di Torino, 17-19 November 2015.

The present study aims to investigate, by numerical simulations, the potentiality of plasma actuators to reattach the separated flow along a low pressure turbine blade, at low-Reynolds number. The flow over a curved wall plate, installed in a low Reynolds wind tunnel to simulate the suction surface of a low-pressure turbine blade, was simulated. The installation on the profile of plasma actuators has been considered. Numerical simulations on a three dimensional computational grid were performed in absence and in presence of actuation. The three dimensional case without actuation was validated with experimental data found in the literature. In presence of actuation, the plasma induced force was modeled and introduced as a source term in the momentum Navier-Stokes equation; the corresponding two dimensional numerical flow simulations were validated with the experimental data obtained by Particle Image Velocimetry and Laser Doppler Velocimetry. The same force was applied in the three dimensional simulations. Two different plasma actuator configurations have been investigated: a micro single dielectric barrier discharge and a micro linear plasma synthetic jet with and without thrust vectoring. By using these devices the separation of the flow has been considerably reduced.

"A comparison between micro linear plasma synthetic jets and conventional DBD plasma actuators for separation control in a low pressure turbine", De Giorgi Maria Grazia, Ficarella Antonio, Marra Fedele, Pescini Elisa, Traficante Stefania. ASME-ATI-UIT 2015 Conference on Thermal Energy Systems: Production, Storage, Utilization and the Environment. p. 1-8, Napoli:asme-ati-uit, ISBN: 978-88-98273-17-1, Napoli, 17-20 Maggio 2015.

At high altitudes the boundary layer of the blades of low-pressure turbine of small gas turbines for aircraft propulsion could be dominated by laminar flow and susceptible to flow separation and secondary vortices, with a reduction of turbine performance. The present study concerns the active flow control using plasma actuators to reattach the simulated separation flow over the suction surface of a low-pressure turbine blade at low Reynolds number. Different actuator geometries have been studied: a macro single dielectric barrier discharge (SDBD), a micro SDBD and a micro linear plasma synthetic jet (L-PSJ) with and without thrust vectoring. In particular, the micro plasma actuator was realized and experimentally characterized by measuring the induced wall-jet with Particle Image Velocimetry (PIV) and by evaluating the electrical power consumption. The numerical modelling was used to assess and compare the performances of the different configurations in the separation control. In presence of these active flow control devices the separated flow was successfully reduced.

"Optimization of micro single dielectric barrier discharge plasma actuator models based on experimental velocity and body force fields", Pescini, Elisa; Martínez, David S.;De Giorgi, Maria Grazia; Ficarella Antonio, ACTA ASTRONAUTICA, 116, 318-332, 2015.

Recently, the Micro Single Dielectric Barrier Discharge Plasma Actuator has become attractive for application in aeronautics and micropopulsion thrusters. The present work carried out a preliminary characterization of such device, acting on initially quiescent air by experimental and numerical approaches. Sinusoidal voltage excitation with amplitude up to 7 kV and frequency up to 2.5 kHz was applied. The induced flow was investigated by particle image velocimetry and the measured velocity fields were used to estimate experimentally the time-averaged induced body force distributions by a differential method. Plasma induced forces were modeled by following three different approaches, later implemented as a source term in the Navier–Stokes equations for the fluid flow simulations. Potentialities, advantages and disadvantages of the considered force modeling methods were investigated. Quantitative comparison of the experimental and numerical induced force, as well as of the velocity fields, allowed establishing which model best predicted the actuator effects. The algebraic Dual Potential Model provided a good agreement between experimental and simulated results, in terms of flow velocities and thickness of the induced wall-jet. The downstream decay of the wall-jet velocity, experimentally observed, was also successfully predicted. A maximum induced velocity of ≈2 m/s was obtained and a jet thickness of ≈3 mm.

"Investigation of a Micro Dielectric Barrier Discharge Plasma Actuator for Regional Aircraft Active Flow Control", Pescini, E. ; Francioso, L. ; De Giorgi, M.G. ; Ficarella, A., IEEE TRANSACTIONS ON PLASMA SCIENCE, 43, 3668-3680, 2015.

This paper reports a multitechnique investigation of a micro dielectric barrier discharge plasma actuator (DBDPA) as a promising system to control separated flows. The device was manufactured through a photolithographic technique and its performances and capabilities were compared with the ones of conventional macro DBDPAs. Alternate current operation under sinusoidal voltage excitation was studied in the absence of external flow by means of many experimental techniques like discharge imaging, flow visualizations, particle image velocimetry, infrared thermography, and electrical characterization. The influence of the operating parameters was investigated. The main results underlined that an increase in the voltage amplitude or frequency brought to a rise in the maximum induced velocity, electrical power dissipation, and actuator surface temperature. Moreover, it was assessed that the small heating of the micro DBDPA did not affect the actuated flow. A jet velocity up to 1.36 m/s was obtained at a 9.01 W/m electrical power dissipation per unit electrode length. The device realized by microelectronic fabrication technology allowed reaching a flow velocity magnitude comparable with the one of conventional macro DBDPAs, with a reduction in applied voltage, power dissipation, and actuator size. Furthermore, the induced wall jet was more confined in the area in proximity of the device, because of the limited plasma discharge extension.

"Dissipated power and induced velocity fields data of a micro single dielectric barrier discharge plasma actuator for active flow control", Pescini, Elisa; Martínez,  David S; De Giorgi, Maria Grazia; Francioso, Luca; Ficarella, Antonio,DATA IN BRIEF, 5, 65-70, 2015.

In recent years, single dielectric barrier discharge (SDBD) plasma actuators have gained great interest among all the active flow control devices typically employed in aerospace and turbomachinery applications. Compared with the macro SDBDs, the micro single dielectric barrier discharge (MSDBD) actuators showed a higher efficiency in conversion of input electrical power to delivered mechanical power. This article provides data regarding the performances of a MSDBD plasma actuator. The power dissipation values and the experimental and numerical induced velocity fields are provided. 

"Comparison between synthetic jets and continuous jets for active flow control: Application on a NACA 0015 and a compressor stator cascade", De Giorgi M.G.; De Luca C.G.; Ficarella A.; Marra F., AEROSPACE SCIENCE AND TECHNOLOGY, 43, 256-280, 2015.

A numerical investigation is performed to analyse the suppression of the boundary layer separation first on a NACA 0015 airfoil and subsequently in a highly loaded subsonic compressor stator cascade using two different active flow control techniques: synthetic jet actuators (SJA) and continuous jet actuators (CJA). In particular, the effort is concentrated towards understanding the physics of the phenomenon, which makes one configuration perform better than the other one as an active flow control (AFC) system. The analysis of the interaction of the jet with the boundary layer was performed, with a description of the vortical structures, which are beneficial for the mixing of the boundary layer and the entrainment of energy from the external flow towards the most inner layers. Regarding airfoils, the comparisons of the SJA with the CJA were performed considering two similarity conditions: identical momentum coefficients and identical amounts of energy fed into the cross flow. Finally, the flow behaviour and the topology structure in a highly loaded compressor cascade with and without AFC are examined. Active flow control using synthetic jet actuators proved to be attractive because it could exploit the unsteady phenomena, inhibit the separation, improve and control the aerodynamics of the flow in both external aerodynamics and turbomachinery components. Furthermore, comparing the CJA and the SJA for active flow control on the compressor at similar momentum coefficients shows that the relative reduction of the total pressure losses for the SJA is approximately twice as large as that for the CJA. It should also be remarked that even if the two AFC configurations present similar effects on the reduction of secondary flow structures, the SJA is more advantageous than the CJA from the regaining energy viewpoint.

2014

“Development of Dielectric Barrier Discharge Actuators Arrays for Boundary Layer Streaks Production”, Elisa Pescini, Maria Grazia De Giorgi, Philippe Lavoie, Luca Francioso, in proceedings of the 1000 Island Fluids Mechanics Meeting, May 30‐June 1, 2014, Giananoque, Ontario, Canada.

The present study intends to investigate the boundary layer characteristics to assess the potentiality of the single dielectric barrier discharge plasma actuators (SDBDPAs) to reattach the separated flow at low Reynolds numbers. The effect of the actuator geometrical parameters and of the Reynolds number on the device control authority was experimentally investigated. For this aim, a curved wall plate, which profile shape was designed to reproduce the suction surface of a low-pressure turbine (LPT) blade, was installed in the test section of a closed loop wind tunnel and a groove was made over it, at the front of the adverse pressure gradient region, for allocating a SDBDPA. Three actuators, characterized by different streamwise width, were manufactured by photolithography technique and they were tested. The velocity flow field, in both presence and absence of external flow, was investigated by particle image velocimetry (PIV) measurements. When the actuator was turned on, a sinusoidal voltage excitation with amplitude of 8 kV and frequency of 2 kHz was applied and the dissipated power ( ) was retrieved by electrical characterization.

"Experimental and Numerical Analysis of a Micro Plasma Actuator for Active Flow Control in Turbomachinery", E. Pescini, M.G. De Giorgi, F. Marra; A. Ficarella. Proceedings of ASME Turbo Expo 2014: Turbine Technical Conference and Exposition GT2014, June 16 – 20, Düsseldorf, Germany GT2014-25337, 2014.

Nowadays several active flow control systems, particularly dielectric barrier discharge plasma actuators, appear to be effective for the control of flow stream separation and to improve performance of turbomachinery. However these applications require high actuation strength, higher than the one generated by conventional macro plasma actuators. Research is actually improving the design of plasma actuator in order to enhance the flow control capability and reduce the power consumption. In this contest, this work concerns the implementation of a micro plasma actuator for the active control in a compressor cascade. For this aim, firstly the micro actuator was developed and an experimental characterization of the flow induced by the device was done. The induced flow field was studied by means of Particle Image Velocimetry and Laser Doppler Velocimetry. The dissipated power was also evaluated. Experimental results were used to validate a multi-physics numerical model for the prediction of the body forces induced by the plasma actuator. Finally, the obtained body force field was used for modeling the separation control by means of the micro plasma actuator in a highly-loaded subsonic compressor stator.

"Effect of a micro dielectric barrier discharge plasma actuator on quiescent flow", E. Pescini, L. Francioso, M.G. De Giorgi, A. Sciolti, A. Ficarella, IET Science, Measurement & Technology, Volume 8, Issue 3, pp. 135 – 142; DOI:  10.1049/iet-smt.2013.0131, May 2014.

A dielectric barrier discharge plasma actuator (PA) was designed and manufactured with microscale dimensions using photolithographic process on fibre glass substrate. AC operation under sinusoidal voltage was investigated experimentally by means of electrical characterisation, smoke flow visualisations and particle image velocimetry. The performances of the micro PA were evaluated and compared with the ones of a macro PA found in this literature. The velocity induced by the micro PA was comparable with the macro PA one, but with lower applied voltage, electrical power dissipation and actuator size. This is particularly interesting for potential applications in turbomachinery.

2013

"Comparing Plasma Actuator Models And Application On A Compressor Cascade", D. Bello, M.G. De Giorgi, S. Traficante, A. Ficarella, ISABE2013-21st ISABE Conference, Busan Korea, 9-13 September 2013.

An important issue in the study of active flow control by dielectric barrier discharge plasma actuators is the implementation of a model that accurately predicts the induced flow. In this study different numerical plasma models were compared, by estimating the Lorentz force generated by the plasma without spatially resolving the plasma chemistry directly. The body force distribution computed with each model was introduced in the CFD code to compute the resulting velocity field induced by the plasma actuators on a quiescent flow on a flat plate. The limit of many of these models is the necessity to calibrate some parameters, as the charge distribution on the dielectric surface. In the present study a unique method has been defined to establish this parameter, by applying an unsteady plasma model based only on the solution of the electrostatic potential field. Steady linear body fields were also estimated based on results of the previous unsteady plasma models and applied to simulate plasma effects on a highly loaded compressor cascade. By the active flow control the secondary flow is successfully reduced, resulting in a decreased total pressure loss and a rise in the static pressure.

"Microscale Dielectric Barrier Discharge Plasma Actuators: Experimental Characterization", Elisa Pescini, Maria Grazia De Giorgi, Luca Francioso, and Antonio Ficarella, 4th Imeko TC19 Symposium on Environmental Instrumentation and Measurements, Protecting Environment, Climate Changes and Pollution Control, June 3-4, Lecce, Italy, 2013.

Dielectric Barrier Discharge (DBD) plasma devices have been designed and manufactured with micro scale dimensions through photolithographic process on fiber glass substrate. AC operation under sinusoidal voltage up to 14 kVpp and carrier frequency up to 2.5 kHz has been investigated experimentally by means of smoke flow visualizations and Particle Image Velocimetry. Velocity profiles, maximum induced velocity and induced body force have been calculated. A comparison between the microactuator and a conventional macroactuator has been performed. It has been demonstrated that the microactuator produces velocities on the order of the macro scale actuator with a significant reduction in inception voltage, size and mass. This leads to a simpler and a less intrusive dispositive.

2012

"NUMERICAL INVESTIGATIONS OF AFC METHODS ON HIGHLY LOADED COMPRESSOR CASCADE", M.G. De Giorgi, S. Traficante, D. Bello, A. Ficarella, 67° Congresso Annuale ATI, Trieste (Italy), Sept. 11-14, 2012.

In the design of aircraft propulsion systems, particular attention is given to improving efficiency, to increasing the payload and to reducing noise and pollutants. Today, active and passive boundary layer control systems are studied and widely used to increase external aerodynamics efficiency. Particularly, those systems appear to be effective for the control of separation of flow stream, to reduce pressure losses and to improve efficiency and performance of engine. In this work a CFD analysis is applied to investigate the increase of pressure rise by suppression of boundary layer separation into a highly-loaded subsonic compressor stator cascade, by different active flow control techniques: pulsed jet, synthetic jet and plasma actuator. In literature, several works have investigated the use of these actuators on airfoil, but only few studies have compared their performance. Active flow control devices are installed at two different locations: end walls near the leading edge (with the aim to control secondary flow structures) and blade suction side (to reduce the flow separation at the trailing edge of the blade). The best actuators configuration appeared to be the combined forcing at side wall and suction side. Concerning pulsed/synthetic jet actuators, a suction/blowing type boundary condition is used, imposing a prescribed sinusoidal velocity depending on velocity amplitude, jet frequency and jet angle. Concerning plasma actuation, the effect is modeled into numerical flow solvers by adding the paraelectric plasma body force into momentum equation. The plasma, generated by Dielectric Barrier Discharge, acts as a momentum source to boundary layer allowing it to remain attached throughout a larger portion of blade.

"ACTIVE FLOW CONTROL TECHNIQUES ON A STATOR COMPRESSOR CASCADE: A COMPARISON BETWEEN SYNTHETIC JET AND PLASMA ACTUATORS", Maria Grazia De Giorgi, Stefania Traficante, Carla De Luca, Daniela Bello, Antonio Ficarella, GT2012-69535, Proceedings of ASME Turbo Expo 2012 - GT2012, June 11-15, Copenaghen, Denmark, 2012.

In this work a CFD analysis is applied to study the suppression of the boundary layer separation into a highly-loaded subsonic compressor stator cascade, by different active flow control techniques. Active flow control techniques have the potential to delay separation and to increase the pressure ratio. In particular three different techniques have been applied: the actuation by steady jet, by zero net mass flux Synthetic Jet (SJA) and by plasma actuator. Several works have investigated the use of synthetic jet and plasma actuators on the airfoil, but only few studies have compared the effect of these devices. Concerning the synthetic jet actuator, a suction/blowing type boundary condition is used, imposing a prescribed sinusoidal velocity depending on velocity amplitude, jet frequency and jet angle of ejection with respect to the wall. Concerning the plasma actuation, the effect is modeled into numerical flow solvers by adding the paraelectric force that represents the plasma force into the momentum equation. The plasma, generated by Dielectric Barrier Discharge, acts as a momentum source to the boundary layer allowing it to remain attached throughout a larger portion of the airfoil. The time-averaged body force component, acting on the fluid, depends on the frequency and on the applied voltage, the charge density, the electrical field and the dimensional properties of the actuator, like width of the electrodes and gap between the electrodes. Using this numerical model, the effect of plasma actuators to suppress the flow separation over the blade has been investigated, increasing the turbo-machinery performance too. Finally, the comparison between the different actuation devices shows that, reducing the secondary flow structures, each actuation technique beneficially affects the performance of the stator compressor cascade, even if in the steady jet the costs are relevant.

2011

"Modellazione numerica degli effetti da scarica a barriera per il controllo attivo del flusso su profili alari", M. G. De Giorgi, S. Traficante, A. Ficarella, ATI 2011, 66° Congresso Nazionale ATI – Rende (Cosenza), 5 - 9 Settembre 2011.

In questa memoria è preso in esame il controllo attivo del flusso su un profilo aerodinamico attraverso attuatori al plasma. Tali dispositivi generano plasma nello strato limite del profilo, inducendo una scarica a barriera a pressione atmosferica, permettendo il trasferimento di energia dal campo elettrico alle particelle neutre dello strato limite, dove il flusso è in procinto di separazione dal profilo (interazione Elettroidrodinamica – EHD), e influenzando il profilo di velocità nello strato limite. Gli elettrodi eccitati ionizzano, seppure debolmente, l’aria circostante ed il campo elettrico prodotto dagli stessi genera un vettore forza che agisce sul flusso esterno. Questa forza può essere espressa in termini di potenziale applicato ed essere considerata nelle equazioni di Navier-Stokes. Numerosi sono i lavori che hanno analizzato l’effetto di attuatori al plasma attraverso l’implementazione di modelli numerici semplificati che studiano l’effetto del plasma come forza volumetrica costante nel tempo e nello spazio, oppure modelli che analizzano la forza elettro-idro-dinamica che genera il plasma, forza elettrica linearizzata e dipendente dal campo elettrico. Nel presente lavoro, invece, è stato implementato un modello numerico in cui la forza, generata dal plasma, è ottenuta come prodotto della densità di carica e del campo elettrico, risolvendo l’equazione di Maxwell per ottenere il campo elettrico generato dal potenziale applicato agli elettrodi e un’ulteriore equazione che tiene in considerazione la densità di carica, che rappresenta la densità del plasma. Inizialmente il suddetto modello è stato simulato su una piastra con un attuatore al plasma, composto da due elettrodi e da materiale dielettrico. Successivamente, la modellazione numerica è stata implementata su un profilo NACA 0015, con attuatore al plasma posizionato in prossimità del bordo di attacco, che ha comportato una quasi scomparsa della zona di separazione del fluido dalla superficie ed una riduzione delle zone di turbolenza del fluido in movimento sul profilo alare.

"Attuatori a fluido per il controllo attivo di flussi aerodinamici", M. G. De Giorgi, C. De Luca, A. Ficarella, ATI 2011, 66° Congresso Nazionale ATI – Rende (Cosenza), 5 - 9 Settembre 2011.

Questo lavoro ha come obiettivo il controllo attivo di flussi aerodinamici mediante l’impiego di attuatori a getto sintetico (SJA – Synthetic Jet Actuators), per possibili applicazioni in campo aeronautico. In particolare, é stato caratterizzato il campo di moto in prossimità di un profilo alare NACA 0015 in condizioni di stallo aerodinamico, con l’obiettivo di analizzare le prestazioni aerodinamiche in presenza di un attuatore a getto sintetico allocato al 12% della lunghezza della corda a partire dal bordo di attacco. Lo studio, dapprima nel caso non controllato, è stato condotto per angoli di attacco compresi fra 12° e 22° a numero di Reynolds pari a Re =8.96 x 105. È stata inoltre effettuata un’analisi di sensibilità dei parametri dell’attuatore (angolo di inclinazione del getto rispetto alla parete del profilo, frequenza ed ampiezza del segnale di attuazione) in corrispondenza di un angolo di attacco pari a 16° (condizione di post-stallo), con l’intento di aumentare il coefficiente di portanza e di ritardare il distacco della vena fluida. Nella scelta dei valori ottimali si è tenuto conto non solo della configurazione con la migliore prestazione aerodinamica, ma anche del fatto che, al fine di poter applicare tale tecnica su un sistema aeronautico, ci sono ulteriori considerazioni da tener farsi. Relativamente all’ampiezza del getto, un picco troppo elevato nel profilo di velocità del getto, deve poter essere compatibile con il peso e le dimensioni dell’attuatore, e la sua realizzazione. Analogamente frequenze di attuazione troppo elevate possono comportare un aumento della potenza richiesta dal dispositivo, senza un aumento eccessivo delle prestazioni aerodinamiche del getto sintetico. Si ottiene, in questo modo, una configurazione ottimale del dispositivo con un aumento significativo della portanza massima (+38% rispetto al caso non controllato) e un ritardo del verificarsi del fenomeno di stallo.

PERFORMANCE IMPROVEMENT OF TURBOMACHINERY USING PLASMA ACTUATORS, M. G. De Giorgi, S. Traficante, A. Ficarella, GT2011- 46413, ASME Turbo Expo 2011, June 6-10, 2011, Vancouver, Canada.

This work deals with the computational modeling of the single dielectric barrier discharge (SDBD) plasma actuator and its applications as a flow actuator. In the literature, plasma actuators have been used especially in order to control boundary layer separation. The plasma acts as a momentum source to the boundary layer allowing it to remain attached throughout a large portion of the airfoil.

The RANS simulations are performed using a CFD code in which the plasma force have been modeled as paraelectric force acting on the charged particles in the working flow.

Using this numerical model, different cases have been simulated on NACA 0015 airfoil, depending on the direction of the force, to study the effect of the force on the flow and on the boundary layer.

The best flow control solutions have been displayed when body force component in the direction straight along the flow is positive and the component normal to the flow is considered. Finally, this numerical simulation methodology has been used for the investigations on the potential of plasma actuators, to suppress the flow separation over a compressor blade.

Specifically, the analysis has been focused to evaluate the increasing of the compressor performance depending on the actuator strength and position on the blade.

ACTIVE FLOW CONTROL USING PLASMA ACTUATORS IN GAS TURBINE ENGINE, Maria Grazia De Giorgi, Stefania Traficante, Antonio Ficarella, ISABE-2011-1732, 20th ISABE Conference, September 12-16, 2011, Gothenburg, Sweden.

This study is focused on the active flow control in the internal flow of turbo-jet engines by Dielectric Barrier Discharges Actuators. In particular the application of this techniques has been studied with the aim of improving the aerodynamic behavior of compressor blades by reducing, or even eliminating, flow separation.

A numerical electrostatic model has been implemented in the CFD code, to investigate the aerodynamic behaviour of a transonic compressor rotor with and without plasma actuators.