Stefano Campilongo

Assessment of the Combustion Behavior of a Pilot-Scale Gas Turbine Burner Using Image Processing

Experimental investigations were performed on a non-premixed liquid fuel-lean burner. The present work aims to the development of a methodology for the recognition of flame instability regimes in industrial and aeronautical burners. Instability, in fact, is an unpleasant aspect of combustive system that negatively impacts on combustion efficiency. The online monitoring of the occurrence of instability conditions, permits to adjust combustion parameters (as fuel or air mass flow, temperature, pressure, etc.) and to stabilize again the flame.High speed visualization systems are promising methods for on-line combustion monitoring.In this study two high speed visualization systems in the visible range and in the infrared spectral region were applied to characterize combustion efficiency and flame stability.Different processing techniques were used to extract representative data from flame images.Wavelet Decomposition and Spectral analysis of pixel intensities of flame images were used for feature extraction. Finally a statistical analysis was performed to identify the most unstable regions of the flame by the pixel intensity variance.Copyright

Lean Blowout Sensing and Plasma Actuation of Non-Premixed Flames

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.

Experimental data regarding the characterization of the flame behavior near lean blowout in a non-premixed liquid fuel burner.

The article presents the data related to the flame acquisitions in a liquid-fuel gas turbine derived burner operating in non-premixed mode under three different equivalence fuel/air ratio, which corresponds to a richer, an intermediate, and an ultra-lean condition, near lean blowout (LBO). The data were collected with two high speed visualization systems which acquired in the visible (VIS) and in the infrared (NIR) spectral region. Furthermore chemiluminescence measurements, which have been performed with a photomultiplier (PMT), equipped with an OH* filter, and gas exhaust measurements were also given. For each acquisition the data were related to operating parameters as pressure, temperature and equivalent fuel/air ratio. The data are related to the research article “Image processing for the characterization of flame stability in a non-premixed liquid fuel burner near lean blowout” in Aerospace Science and Technology [1].

Embedded sensor/actuator system for aircraft active flow separation control

This work reports on finite element method (FEM) design and fabrication of low cost capacitive pressure sensors for aircraft applications; this work is part of a research activity aimed to develop an embedded sensor-actuator system composed by multi-measure points pressure sensors for flow turbulence detection and coupled plasma actuators for control of separated flows on aircraft wings structures. The system uses sensors feedback information to provide fast reattachment of boundary layer separation flow on the suction surface of regional aircraft vehicles. Flow separation has great impact on the performance and safety of an aircraft and it can be predicted by quantifying the pressure gradients along the wing wall. Considering the absolute pressure values on a NACA 0012 profile as a function of the angle of attack, high sensitivity measurements of differential pressure can be obtained by positioning the sensor-nodes at points on the airfoil surface where the P/Pstall ratio between the absolute pressure at different angles of attack and the pressure measured in stall condition is maximized.

Investigating Flow Dynamics with Wireless Pressure Sensors Network

Wireless sensors networks enable the chance to investigate with enhanced freedom physical phenomena, aiming to increase the informative content obtained by sensors measurements. In this work we will focus on a system allowing to experimentally measure pressure profiles obtained from sensor nodes deployed on a NACA0012 aircraft wing model. By exploiting measurements gathered from sensors, allowing to measure pressure fluctuations of ±600Pa with a resolution of 4Pa, together with results obtained by Computational Fluid Dynamics (CFD) models, the system enables extracting flow profile, thus obtaining information on flow separation and stall phenomenon. Wireless measures are delivered with an enhanced version of IEEE802.15.4e, allowing to decrease power consumption by a factor of 7. Packet routing, based on Routing Protocol for Low-Power and Lossy Networks (RPL), has been improved by means of a newly introduced Lifetime and Latency Aggregatable Metric (L2AM) leading to a 18% increased network lifetime.

Ultra Lean Combustion Characterization in a Pilot-Scale Gas Turbine Burner Using Image Processing Techniques

The aim of the present investigation is the characterization of the behavior of a lean partially-premixed liquid fuel gas turbine near lean blowout limit.At this combustion regime the onset of instability will occur with negative impacts on combustion efficiency.The identification of the instability occurrence permits an efficient flame control adjusting the combustion parameters (as fuel or air mass flow, temperature, pressure, etc.) to stabilize the flame or designing opportunely flame control system.High-speed images of the flame under stable and near blowout condition were captured in conjunction with simultaneous optical data in order to better understand the phenomenology of the flame blowout process and the onset of instability.In particular the experimental characterization was performed through a High Speed Digital Camera, an Infrared camera and a Photomultiplier Tube (PMT) in association with the use of optical filter (OH*). The data collected with these instrumentations produce useful features for the development of an efficient tool for the flame control in industrial and aeronautical burners. The images acquired by the different cameras were processed considering the luminosity signal of each pixel and evaluating the frequency behavior, the variations of amplitude of the signals and some other descriptive parameters able to define the regime of the flame. Spectral analysis and Wavelet transform of pixel intensities of flame images were used and entropy and energy contents were evaluated. The spatial maps of the different spectral and statistical parameters were shown at different fuel/air equivalence ratio. The OH* emissions data measured by the PMT were processed and compared with the data obtained from the images processing.Copyright

Predictions of Operational Degradation of the Fan Stage of an Aircraft Engine Due to Particulate Ingestion

A numerical evaluation of the effects of volcanic ash ingestion in a turbofan engine was carried out, with particular regard to the prediction of the erosion damage to fan blades. The ash concentration level examined in the study was below the flight limit because the aim of this study is to investigate the damage due to long-term exposure to low concentration levels. The work aims to the implementation of a numerical methodology that takes into account the geometry change of the fan blades during the exposure to volcanic ash. A dimensional and morphological characterization of a real volcanic ash sample from the Mount Etna volcano has been performed to model the particle flow dynamics using a computational fluid dynamics (CFD) code. The fan performance in terms of the total pressure increase was calculated for both the baseline and damaged geometries to quantify the performance deterioration trend with respect to the particle exposure time. For the calculation of the eroded fan performance, two different numerical approaches were considered. In the first approach, the erosion rate (ER) was evaluated based on the initial blade geometry and was held constant. In the second approach, the ER was updated as the erosion of the blade continued. The second approach shows a higher deterioration of the pressure rise across the fan, suggesting that the variation of the ER due to the blade shape modification cannot be neglected in the calculations.

Experimental and Numerical Study of Particle Ingestion in Aircraft Engine

This study is focused on volcanic ash ingestion in aircraft engines, that can lead to slow but constant deterioration in engine performance and engine failure because of the mechanical damages to the wall surface. In particular the particles that impact on blades surfaces cause erosion damage and permanent losses in engine performance. Aircraft engine fans could be severely damaged by the ash flow.. In order to clarify the erosion phenomenon the fan has been simulated through the general-purpose CFD code and the numerical simulations were performed using the Reynolds–Averaged Navier–Stokes (RANS). After validating the numerical modeling of the flow without erosion by comparisons with experimental data in literature, a surface injection of a discrete phase has been introduced in order to evaluate particle ingestion of volcanic ash. This phenomenon is a typical gas-particle two-phase turbulent flow and a multi-physics problem where the flow field, particle trajectory and wall deformation interact with among others. A wide experimental investigation has been carried out on an ash sample from Etna volcano. In particular a sieve analysis to obtain particles dimensional distribution and an analysis of SEM images to calculate particles shape factor. These data were used to modeling the particle injection in the CFD model. The numerical investigation was aimed to clarify the effects of particle erosion and to evaluate the change of the flow field in the case of eroded blades. By erosion rate patterns, the eroded mass was estimated and it was used to model the eroded geometry, by a user routine implemented in the dynamic mesh module of the code. So the performances of the damaged fan were estimated and compared with the baseline geometry without erosion.Copyright