1,720,999 research outputs found
EXPERIMENTAL VALIDATION OF THE MULTI WAVELENGTH LIGHT EXTINCTION TECHNIQUE ON POTASSIUM CHLORIDE NANOPARTICLES
No full textNowadays, 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
Experimental and Numerical Characterization of Dielectric Barrier Discharge Plasma Actuators for Active Flow Control of Boundary Layer Separation and Bypass Transition
No full textThe 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
Investigation of a Micro Dielectric Barrier Discharge Plasma Actuator for Regional Aircraft Active Flow Control
No full textThis 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
Micro DBD plasma actuators for flow separation control on a low pressure turbine at high altitude flight operating conditions of aircraft engines
Full text linkAbstract 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
Plasma actuator scaling down to improve its energy conversion efficiency for active flow control in modern turbojet engines compressors
No full textThe 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 frequenc
MICROSCALE DIELECTRIC BARRIER DISCHARGE PLASMA ACTUATORS: EXPERIMENTAL CHARACTERIZATION
Full text linkDielectric 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
DEVELOPMENT OF DIELECTRIC BARRIER DISCHARGE ACTUATORS ARRAYS FOR BOUNDARY LAYER STREAKS PRODUCTION
No full textThe presented work consists in the development
of dielectric barrier discharge (DBD) plasma actuators
arrays for introducing streaks in a laminar boundary
layer.
A single DBD plasma actuator is composed of two
electrodes separated by a dielectric layer: one
electrode is supplied with a high voltage waveform
and exposed to the surrounding flow and the other is
grounded and completely covered by an insulating
material. Under operation, an electric field is created
and the surrounding air is weakly ionized. It results in
a net body force that acts on the ambient (neutrally
charged) air, inducing a flow jet of few m/s. Different
geometrical arrangements can be adopted, each one
aiming to a characteristic active flow control
application.
Spanwise arrays of symmetric plasma actuatorsi
can be used for the purpose of generating spanwiseperiodic
counter-rotating vortices. A typical application
regards the stabilization of a laminar boundary layer
to delay transition. In Hanson et al. ii and Grundman
et al.iii,iv these dispositives were then used for
attenuating the velocity streaks inherent to bypass
transition, by superimposing a disturbance of the
opposite sense.
In Osmokrovic et al.i the influence the of excitation
parameters, electrode geometry and dielectric
thicknesses on the induced velocity streaks was
tested. Moreover, the effect of the actuator length L,
spanwise spacing Δz and some operating
parameters, like the free stream velocity U∞, are still
not well understood.
A dedicated activity was devoted for the design
and fabrication of different array geometries. They will
be then tested in different test conditions (applied
voltage amplitude, frequency and free stream
velocity)
Lean Blowout Sensing and Plasma Actuation of Non-Premixed Flames
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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
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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 plasm
Investigation of the boundary layer characteristics for assessing the DBD plasma actuator control of the separated flow at low Reynolds numbers
Full text linkThe 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
Experimental and Numerical Study of Plasma Based Flow Control for Low Pressure Gas Turbines Operating at Low Reynolds Numbers
No full textHigh 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
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