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.

The present work introduces a method for flow and noise control using plasma actuation. The Single Dielectric Barrier Discharge Plasma Actuator (SDBDPA) device is object of study. A discussion of potential applications in flow and noise control in aerospace field is initially done. Then experimental results on separation control applications are presented. The investigated, SDBDPA was manufactured by means of photolithographic technique. Particular attention was paid in materials selection because of possible degradation in plasma environment. The device separation control authority was investigated locating it on a curved plate with a shape designed to reproduce the suction surface of a low pressure turbine (LPT) rotor blade. The changes in the device performances with aging were quantified by monitoring in time the actuator power consumption. Scanning electron microscope (SEM) images on the new and used device were also used to complement the investigation.

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.

The present work is focused on the investigation of an alternate current driven single dielectric barrier discharge plasma actuator (AC-SDBDPA) for the control of separated flow at Reynolds numbers up to 2·104. Laminar boundary layer separation typically occurs on the suction surface of the low pressure turbines (LPT) blades when operating at high altitude cruise conditions, as the Reynolds number can drop below 2.5·104. In this context, the implementation of an active boundary layer control system able to operate in suppressing separation — only at the critical Reynolds numbers — is of great interest. The SDBDPA was manufactured by means of the photolithographic technique, which ensured a thin metal deposition with high manufacturing reliability control. Actuator operation under sinusoidal voltage at 8 kV amplitude and 2 kHz frequency was considered. Investigations were performed in a closed loop wind tunnel. A curved plate with a shape designed to reproduce the suction surface of a LPT was mounted directly over the bottom wall of the test section. The SDBDPA was inserted in a groove made at the middle of the curved plate, located at the front side of the adverse pressure gradient region. The flow pattern and velocities in absence of actuation were experimentally measured by a two-dimensional (2-D) particle image velocimetry (PIV) system and a laser Doppler velocimetry (LDV) system. PIV measurements were performed in presence of actuation. Simultaneously to the velocity measurements, the voltage applied to the AC-SDBDPA and the discharge current flowing through the circuit were acquired in order to determine the power dissipated by the device. The experimental data were supported by computational fluid dynamics (CFD) simulations based on the finite volume method. In order to deeply investigate the effect of flow separation control by the AC-SDBDPA on the LPT blade performances, the viscous and unsteady Reynolds-averaged Navier-Stokes equations were solved to predict the characteristics of the flow with and without actuation. The actuation effect was modelled as a time-constant body force calculated prior to the fluid flow simulations by using the dual potential algebraic model. The experimental data were used to calibrate and successfully validate the numerical model. An unsteady RANS (URANS) approach, using the k-ω Lam and Bremhorst Low-Reynolds turbulence model was employed, accounting with the main transient flow structures. Results showed that the mixing action of the streamwise fluid with higher momentum and the boundary layer fluid with the lower momentum -due to the AC-SDBDPA-led, depending on the tested Reynolds number, to the alleviation or suppression of the boundary layer flow separation which occurred on the suction surface of the LPT blade. The validated numerical model will allow expanding the study of the actuation effect including different locations and multiple devices, saving considerably experimental efforts.

The following work details the experimental and numerical characterization of jet flow control in a coaxial Bunsen burner obtained by an alternate current driven dielectric barrier discharge plasma actuator (AC-DBDPA). Fuel and oxidizer flows could be inverted between the inner circular tube and outer annular tube. Use of the ACDBDPA was intended to improve lean combustion performance. The high voltage (HV) electrode of the ACDBDPA was powered with sinusoidal voltage excitation at 20 kHz frequency and peak-to-peak voltage of about 12 kV. Two burner fueling configurations were tested, characterized by different flow rates in the inner and annular tubes. Values of actuator power dissipation, which were deduced through electrical characterization, ranged between 25 and 28 W. A preliminary analysis of the air-methane flame behavior in presence and absence of plasma actuation was performed. Images of the flame and chemiluminescence emissions showed that the flame luminosity changed and OH radical production increased in presence of the discharge. The thermal and fluid dynamic effects of the plasma actuation on the flow were investigated by means of a non-reacting flow characterization (absence of combustion), where air was used as both fuel and oxidizer. The flow pattern and turbulence in both presence and absence of actuation were studied by laser Doppler velocimetry (LDV) measurements. Flow temperature was acquired using thermocouples. The non-reacting flow experimental results showed that, for a fixed inlet volumetric flow rate, the plasma actuation increased jet velocity and air temperature. Interesting results were obtained from a spectral analysis using the time resolved velocity signals: plasma actuation affected jet mixing and impacted energy distribution between the different flow scales. Complementary numerical simulations identified increasing temperature as primarily responsible for increasing flow velocity. Moreover, numerical predictions permitted better identification of flow regimes under different test conditions.

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 [6] are provided. The present data support and enrich the research article entitled "Optimization of micro single dielectric barrier discharge plasma actuator models based on experimental velocity and body force fields" by Pescini et al.

The reduction of nitric oxides (NOx) in aircraft engines, gas turbines, or internal combustion engines is a main issue in the design of novel combustion systems. The reduction of the NOx emissions might be reached by lean combustion. However, the major issue is the stabilization of the flame under lean conditions. In this context, the present work investigates the possibility of increasing the combustion efficiency of a lean flame through the employment of a plasma actuator, operated by both nanosecond repetitively pulsed high voltage (NRPP) and sinusoidal DBD high voltage (HV). Different actuation conditions have been tested to stabilize and improve the efficiency of a lean non premixed methane/air flame in a Bunsen-type coaxial burner with central fuel jet. An image processing approach was used to characterize the flame behavior near blowout conditions

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.

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 utilised on the used devices to help explain the observed changes in actuator performance. After usage, unexpected degradation effects were ob- served 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 particu- lar, 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 capac- itance 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 powe

The present thesis reports an experimental and numerical characterization of dielectric barrier discharge plasma actuators for active flow control of boundary layer separation and bypass transition.

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.

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.

Nowadays, the control of the particle size distribution and concentration of nanoparticles or nanoparticle aggregates gained special industrial and scientific interest. In this contest, my research project regarded the experimental validation of the Multi Wavelength Extinction Technique (MWLE) on an aerosol of Potassium Chloride nanoparticles. The MWLE is an optical technique that allows in situ real-time monitoring nonintrusively and is able to carry out simultaneous concentration and size measurement in the nanometric size range. In the frame of the present work, a facility for the aerosol generation and for allowing accurate light extinction measurements has been build. As the main goal of this research project was to validate the MWLE, the developed experimental setup allowed also the simultaneous measurement of the same particle flow with both the Muti Wavelenght Light Extinction and with a Scanning Mobility Particle Sizer (SMPS) instrument. The MWLE requires a specific, regularized inversion algorithm for the retrieval of the particle distribution in volume V-PSD, so both the experimental and numerical aspects of the technique were investigated. The Tikhonov NNLS method, with smoothing matrix 0th and 2nd order discrete derivative operator, was applied and the L-curve method (used for finding the optimal regularization parameter) was optimized. All the inversion results gave a volume concentration around one order of magnitude bigger than the one given by the SMPS. Finding the parameter influencing this discrepancy is still a subject of investigation. For this reason normalized distributions, with normalization made with respect to the peak of the distribution, are considered. The comparison with the SMPS, in terms of Normalized Particle Volume Distributions, resulted in good agreement for both the methods, but the 0th order appeared more sensitive to the inversion parameters, like the diameter intervals in which the inversion was applied. Thus the 2nd order was chosen for investigating the effect on the particle size and concentration of the operating parameters like atomization pressure and the ejector feed pressure, which leads to different pressures in the test chamber. Good agreement was found between the MWLE and the SMPS results, in terms of Normalized Particle Volume Distributions and of Volume Mean Diameter D4,3. The measurements showed that, decreasing the atomization pressure, the particle size increases and their concentration decreases. Furthermore, the MWLE showed high sensitivity to the measured transmittance, so an accurate measurement procedure was requested. Summarizing, the objectives of the project have been both the development of the above-mentioned experimental setup and the validation of the MWLE algorithm using a commercial sizing system.

Monitoring and characterization of combustion flames by digital image processing is an active research topic. This study experimentally investigates the feasibility of high speed visualization techniques for combustion instability monitoring in a swirl liquid-fueled lean combustor for different air/fuel ratios. Instability, in fact, is an unpleasant aspect in the combustive system that negatively impacts on combustion efficiency. This work investigates methods for extracting significant parameters using the geometrical and luminous data of the flame images; some flame features are related to the combustion regimes. The stability of the flame is identified using spectral and wavelet-based analysis of the pixel intensities of the flame images. In particular the most flame unstable regions were identified by analyzing the two dimensional maps of different physical quantities. The impact of the fuel/air ratio on the stability of the flame is investigated also by a Monochromator/Photomultiplier system (PMT). The results support the potential of the methods described for flame monitoring.

Abstract Low environmental impact is a main issue in the design of novel combustion systems, as aircraft engines. In this context, the present work investigates the possibility to increase the combustion efficiency of a lean flame through the use of sinusoidally driven dielectric barrier discharge (DBD) plasma actuator. The effect of the plasma discharge on a lean non premixed methane/air flame in a Bunsen-type burner has been studied for two different configurations: the normal diffusive flame (NDF) and the inverse diffusive flame (IDF). The flame behavior was investigated by chemiluminescence imaging through an intensified CCD camera. Optical filters were installed in front of the camera, aiming to selectively record signal from the chemiluminescent species OH*, CH*, or CO2*. This allowed evaluating the changes occurring in presence of plasma actuation in term of flame emissions. It was shown that the plasma effects are significantly influenced by the burner and DBD configuration. A plasma power of approximately 25 W permitted to increase the air mass flow rate at which lean blowout appears; it rose up to 30% for low methane flow rate and up to 10% at high fuel flow rate.

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.

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

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. © 2015 IEEE.

SIBA Get it!(opens in a new window)|View at Publisher| Text export | Download | Save to list | More... IEEE Sensors Journal Volume 16, Issue 10, 15 May 2016, Article number 7426717, Pages 3896-3903 Lean Blowout Sensing and Plasma Actuation of Non-Premixed Flames (Article) De Giorgi, M.G.a , Sciolti, A.a , Campilongo, S.a , Pescini, E.a , Ficarella, A.a , Lovascio, S.b , Dilecce, G.c a Department of Engineering for Innovation, University of Salento, Lecce, Italy b Department of Chemistry, University of Bari, Bari, Italy c Istituto di Nanotecnologie, Consiglio Nazionale delle Ricerche, University of Bari, Bari, Italy View additional affiliations View references (31) Abstract The aim of this paper is the use of optical sensors to recognize lean blowout in a non-premixed methane/air burner, Bunsen-type, and the use of plasma actuators for flame control and stabilization. The burner is optically accessible to permit the imaging acquisitions of the flame region. The plasma actuation regards alternatively the air flow and the fuel flow. The electric field is generated using a fixed configuration of plasma actuator and the dielectric barrier discharge (DBD) but using two different power supplies: a nanosecond repetitively pulsed high voltage (HV) and a sinusoidal DBD HV. The comparison between the two types of actuation is the core of this paper, together with the analysis of the results obtained when actuation acted on the air or on the fuel. For the analysis, the lean blowout (LBO) limits recorded in the presence and absence of plasma actuation to investigate the plasma actuation success. The flame behavior is acquired using a compact digital camera, an intensified charge-coupled device (CCD) in order to capture the differences between the baseline conditions and the actuated cases. It is shown that the plasma significantly allows stabilizing the flame under lean conditions where it would not exist without plasma

Abstract 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.

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.

Preventing the flow separation could enhance the performance of propulsion systems and future civil aircraft. To this end, a fast detection of boundary layer separation is mandatory for a sustainable and successful application of active flow control devices, such as plasma actuators. The present work reports on the design, fabrication and functional tests of low-cost capacitive pressure sensors coupled with dielectric barrier discharge (DBD) plasma actuators to detect and then control flow separation. Finite element method (FEM) simulations were used to obtain information on the deflection and the stress distribution in different-shaped floating membranes. The sensor sensitivity as a function of the pressure load was also calculated by experimental tests. The results of the calibration of different capacitive pressure sensors are reported in this work, together with functional tests in a wind tunnel equipped with a curved wall plate on which a DBD plasma actuator was mounted to control the flow separation. The flow behavior was experimentally investigated by particle image velocimetry (PIV) measurements. Statistical and spectral analysis, applied to the output signals of the pressure sensor placed downstream of the profile leading edge, demonstrated that the sensor is able to discriminate different ionic wind velocity and turbulence conditions. The sensor sensitivity in the 0-100 Pa range was experimentally measured and it ranged between 0.0030 and 0.0046 pF Pa-1 for the best devices

Different input waveforms applied to a Single Dielectric Barrier Discharge Plasma Actuator (SDBDPA) were compared for flow separation control on low-pressure turbines (LPTs). The investigated Reynolds number (Re) was 2·104. The work aim was the device optimization in terms of materials and excitation conditions for enhancing its durability and performances. The SDBDPA was manufactured by microfabrication techniques. Device materials that could withstand the plasma environment were selected. Sine, square and triangle waveforms were compared in terms of actuator dissipated power and induced velocity. At comparable peak-to-peak applied voltage, the sinus outperformed the other waveforms, while the square dissipated the most.

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.

Aim of the present paper is the characterization of a non-premixed methane/air microburner, Bunsen-type, equipped with a plasma actuator for the flame stabilization and the blowoff control. The burner is optically accessible to permit imaging acquisitions of the flame region. The plasma actuation regards the air flow, while the fuel flow is protected by the action of the electric field. The limits of flashback and blowoff were recorded in presence and in absence of the plasma actuation. The flame behavior was acquired using a digital camera in order to capture the differences between the baseline conditions and the actuated cases. The results appear very encouraging for future application in powering micro-devices for aerial and industrial application. It was shown that the plasma significantly allows stabilizing the flame under lean conditions where it would not exist without plasma.

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

Abstract In recent years, the application of plasma actuators in different engineering fields was considered particularly interesting. It was successfully applied for the cold flow control in aero engines and turbo-devices. One important application concerns the use of non-equilibrium plasma for plasma-assisted ignition and combustion control. The reduction of nitric oxides (NOx) in aircraft engines, gas turbines, or internal combustion engines has become a major issue in the development of combustion systems. A way to reduce the NOx emissions is to burn under homogenous lean conditions. However, in these regimes the flame becomes unstable and it leads to incomplete combustion or even extinction. Thus, the major issue becomes to stabilize the flame under lean conditions. In this context the present work aims to demonstrate the possibility to increase the combustion efficiency of a lean flame through the use of nanosecond repetitively pulsed plasma (NRPP). A NRPP produced by electric pulses with amplitude up to 40 kV, pulse rise time lower than 4 ns and repetition rate up to 3.5 kHz has been used to stabilize and improve the efficiency of a lean non premixed methane/air flame in a non-premixed Bunsen-type burner. The burner is optically accessible permitting the imaging acquisitions of the flame region. The flame behavior was acquired using a high rate CCD camera in order to capture the differences between the baseline conditions and the actuated cases. Moreover a post-processing technique showing the jagging of the flame in different conditions was applied to evaluate the changes occurring in presence of plasma actuation in term of flame area weighted respect to the luminosity intensity. It was shown that the plasma significantly allows stabilizing the flame under lean conditions where it would not exist without plasma.

Purpose – Reynolds number in small-size low-pressure turbines (LPT) can drop below 2.5 · 104 at high altitude cruise, which in turn can lead to laminar boundary layer separation on the suction surface of the blades. The purpose of this paper is to investigate the potential of an alternate current (AC)-driven Single Dielectric Barrier Discharge Plasma Actuator (AC-SDBDPA) for boundary layer control on the suction side of a LPT blade, operating at a Reynolds number of 2 · 104. Design/methodology/approach – Experimental and numerical analyses were conducted. The experimental approach comprised the actuator testing over a curved plate with a shape designed to reproduce the suction surface of a LPT blade. A closed loop wind tunnel was employed. Sinusoidal voltage excitation was tested. Planar velocity measurements were performed by laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). The device electrical power dissipation was also calculated. Computational fluid dynamics (CFD) simulations using OpenFOAM© were conducted, modelling the actuator effect as a body force calculated by the dual potential algebraic model. Unsteady RANS (Reynolds Averaged Navier-Stokes equations), also known as URANS approach, with the k- Lam-Bremhorst Low-Reynolds turbulence model was used. Findings – The AC-SDBDPA operation brought to a reduction of the separation region; in particular, the boundary layer thickness and the negative velocity values decreased substantially. Moreover, the flow angle in both the main flow and in the boundary layer was reduced by the plasma control effect. The actuation brought to a reduction of the 17 per cent in the total pressure loss coefficient. The pressure coefficient and skin friction coefficient distributions indicated that under actuation the reattacnment point was displaced upstream, meaning that the flow separation was effectively controlled by the plasma actuation. Adopting slightly higher actuation parameters could bring to a full reattachment of the flow. Practical implications – The work underlines the potentialities of an AC-SDBDPA to control separation in LPTs of aeroengines. Originality/value – The present work sets a methodological framework, in which the validated procedure to obtain the body force model combined with CFD simulations can be used to study a configuration with multiple actuators allocated in array without requiring further experiments.

Small engines will be finding increasing applications in unmanned aerial vehicles (UAVs), drones and helicopters. However, their turbomachines exhibit lower efficiencies than those of large scale engines. In this context, the aerodynamic losses in the low-pressure turbines (LPTs) are largely accountable to flow separation at low Reynolds numbers operation, i.e. in cruise conditions. Active flow control is a promising technology to suppress separation, thus reducing losses, fuel consumption rates and therefore emissions. The present paper is focused on the experimental investigation of the potentialities of a Single Dielectric Barrier Discharge Plasma Actuator (SDBDPA) to reattach the separated flow at a Reynolds number of 2 ·104. The influence of the high voltage (HV) waveform supplying the SDBDPA on both flow separation control and device power dissipation was studied. The investigated SDBDPA was manufactured by microfabrication techniques. Photolithography ensured thin metal deposition with high manufacturing reliability control. Due to the possible device degradation during operation, emphasis was put in selecting thin film materials that could withstand the plasma environment. Schott alkali-free borosilicate glass substrate was chosen as dielectric, while a multilayer tungsten (W)/titanium nitride (TiN) as electrode material. The experimental approach comprised the actuator testing over a curved wall plate, designed with a shape to reproduce the suction surface of a LPT rotor blade and installed in closed loop wind tunnel test section. The SDBDPA was located at the front side of the adverse pressure gradient area, in order to control flow separation. Different HV excitation waveforms (sinus, triangle and square) and amplitudes were tested and compared, aiming to identify the input signal that gave the best flow control authority and device energy conversion efficiency. The applied voltage and the discharge current were acquired in order to determine the actuator dissipated power. Two-dimensional (2-D) flow velocity measurements were carried out by laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). Velocity results showed that the extension of the separation area was reduced by actuation. Moreover, when the actuator was on, the boundary layer thickness and the negative velocity magnitude decreased. Their reduction increased with the applied voltage (i.e. higher power dissipations). At comparable peak-to-peak applied voltages, the sinus waveforms slightly outperformed the other waveforms; however, while the sinus and triangle ones had comparable power dissipation, the square wave always dissipated the most.