New-Concept Gas Turbine Burner Simulation in Moderate Intense Low-Oxygen Combustion Regime

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Modeling and Simulation of an Oxygen-Blown Bubbling Fluidized Bed Gasifier using the Computational Particle-Fluid Dynamics (CPFD) Approach

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Micro Gas Turbine Combustor Performances in CO2/O2 Oxidizer Atmosphere

In fossil fuel energy power plants the oxy-combustion technique, is one of the possible approaches to the problem of greenhouse gases emissions, through the CO2 capture and subsequent storage. It is realized using recirculated flue gas enriched with oxygen as oxidizer and it is suitable more than other techniques to retrofit existing plants. The commercial gas turbine combustors currently available are however designed and optimized for air combustion. In this work, through a series of CFD simulations, a typical commercial micro turbine burner has been tested in oxy-combustion conditions, in order to verify the performances. Through this study it has been shown how these class of combustors cannot be used in an optimal way in terms of efficiency, pollutant emissions and oxygen consumption. Some possible solutions have been also proposed

New-Concept Gas Turbine Burner Simulation in Moderate Intense Low-Oxygen Combustion Regime

In a trapped-vortex combustor (TVC) flame stabilization is achieved through intense internal exhaust gases recirculation, which is promoted by the adoption of cavities. Thanks to its peculiar features, a trapped-vortex burner produces low pressure drop and emissions and it is characterized by extended blow-out limits. The strong mixing of fresh reactants with flue gases due to internal recirculation represents the basis for the establishment of a distributed MILD, i.e. "Moderate Intense Low-Oxygen Dilution Combustion" regime, which is characterized by reduced temperature peaks, volumetric distributed reactions, low NOx emissions and no thermo-acoustic instabilities. Aim of the work is to study the possibility to obtain a MILD regime in our available trapped-vortex device, taking the advantage of the combined effect of TVC strong internal exhaust gases recirculation and of oxy-combustion external exhaust recirculation, attaining the benefits of CO2 capture at the same time. To this end a series of computational fluid dynamics simulations were conducted on our TVC device, in order to understand the influence on combustion of the main operating parameters, such as the equivalence ratio, the level of dilution, the injection temperature, the velocity, etc.. A preheating temperature and a range of oxygen concentrations that at the same time complies with a distributed reactions regime and an efficient combustion were identified for the premixed and non-premixed operating modes

Modeling and Simulation of an Oxygen-Blown Bubbling Fluidized Bed Gasifier using the Computational Particle-Fluid Dynamics (CPFD) Approach

Fluidized beds are conventional components of many industrial processes, such as coal gasification for energy generation and syngas production. Numerical simulations help to properly design and understand the complex multiphase flows occurring in these reactors. Two modeling approaches are usually adopted to simulate multiphase flows: the two fluids Eulerian-Eulerian model and the continuous/discrete Eulerian-Lagrangian model. Since fluidized beds account for an extremely large number of particles, tracking each of them could not assure to get results within a reasonable computational time. The Computational Particle-Fluid Dynamics (CPFD) approach, which belongs to the Eulerian-Lagrangian models class, groups together particles with similar key parameters (e.g. composition, size) into computational units (parcels). Parcel collisions are modeled by an isotropic solid stress function, depending on solid volume fraction. In this paper, the bubbling fluidized bed (BFB) upstream gasifier of the EU research infrastructure ZECOMIX (Zero Emissions of Carbon with Mixed technologies) has been simulated using a CPFD approach via Barracuda® software. The effect of different fluidizing agent injection strategies on bed bubbling and mixing, for non-reacting cases, has been studied. The numerical results for a reacting case have been compared to the available experimental data, gathered during the coal gasification campaign. The model has proved to be very useful in the choice of the more efficient injection configuration that assures a more effective contact of the gas with the solid bed and a good bubbling fluidization regime, together with a satisfactory prediction of the outlet gas composition. The numerical approach has turned out to be robust and time-saving and allowed to dramatically reduce the computational cost with respect the classical two fluids Eulerian-Eulerian models

Tor vergata Synoptic Solar Telescope: Preliminary optical design and spectral characterization

Synoptic telescopes are fundamental tools in solar physics. They are tipically used for high cadence full-disk observations of the Sun at different wavelengths, in order to study the solar activity across the solar cycle. The TSST (Tor vergata Synoptic Solar Telescope) is a new synoptic telescope composed of a Ha filter-based telescope centered at 656 nm and a custom Magneto Optical Filter (MOF)-based telescope centered in the potassium (KI D1) absorption line at 770 nm. Observations of the Ha line are important for the detection of flaring regions and to track the Sun during the acquisition. The aim of the telescope is to monitor the solar activity using the line of sight (LoS) magnetograms and dopplergrams of the solar photosphere produced by the MOF-based telescope. Magnetograms are essential for the study of the geometry of the magnetic field in active regions, while dopplergrams can be used to study the dynamics of the solar lower atmosphere. In this work, we focus our attention on the custom MOF-based telescope. Firstly, we present the optical design of the instrument. It is a refractor telescope with a 80 mm aperture and an effective focal length of ∼1m. We also present details on the preliminary spectral characterization of this instrument at different cell temperatures, which is a mandatory step to calibrate magnetograms and dopplergrams. The results obtained during this first test are in agreement with the peaks separation (∼200 mÅ) and FWHM (∼ 50 mÅ) that we expected

Data reduction pipeline for MOF-based synoptic telescopes

There are strong scientific cases and practical reasons for building ground-based solar synoptic telescopes. Some issues, like the study of solar dynamics and the forecasting of solar flares, benefit from the 3D reconstruction of the Sun's atmosphere and magnetic field. Others, like the monitoring and prediction of space weather, require full disk observations, at the proper sampling rate, combining H-alpha images and Doppler velocity and magnetic field. The synoptic telescopes based on Magneto Optical Filters (MOF) using different lines are capable of measuring the line-of-sight Doppler velocity and magnetic field over the full solar disk at different ranges of height in the Sun's photosphere and low chromosphere. Instruments like the MOTH (Magneto-Optical filters at Two Heights), using a dual-channel based on MOFs operating at 589.0 nm (Na D2 line) and 769.9 nm (K D1 line), the VAMOS instrument (Velocity And Magnetic Observations of the Sun), operating at 769.9 nm (K D1 line), and the future TSST (Tor Vergata Synoptic Solar Telescope), using a dual-channel telescope operating at 656.28 nm (H-alpha line) and at 769.9 nm (K D1 line), allow to face both aspects, the scientific and the operative related to Space Weather applications. The MOTH, VAMOS and TSST data enable a wide variety of studies of the Sun, from seismic probing of the solar interior (sound speed, rotation, details of the tachocline, sub-surface structure of active regions), to the dynamics and magnetic evolution of the lower part of the solar atmosphere (heating of the solar atmosphere, identification of the signatures of solar eruptive events, atmospheric gravity waves, etc.), to the 3D reconstruction of the solar atmosphere and flare locations. However, the use of MOF filters requires special care in calibrating the data for scientific or operational use. This work presents a systematic pipeline that derives from the decennial use of MOF's technology. More in detail, the pipeline is based on data reduction procedures tested and validated on MOTH data acquired at Mees Solar Observatory of the University of Hawaii Haleakala Observatories and at South Pole Solar Observatory (SPSO), at the Amundsen-Scott South Pole Station in Antarctica, during Antarctica Summer Campaign 2016/17

A multiple spacecraft detection of the 2 April 2022 M-class flare and filament eruption during the first close Solar Orbiter perihelion

CONTEXT: The Solar Orbiter mission completed its first remote-sensing observation windows in the spring of 2022. On 2 April 2022, an M-class flare followed by a filament eruption was seen both by the instruments on board the mission and from several observatories in Earth’s orbit, providing an unprecedented view of a flaring region with a large range of observations. AIMS: We aim to understand the nature of the flaring and filament eruption events via the analysis of the available dataset. The complexity of the observed features is compared with the predictions given by the standard flare model in 3D. METHOD: In this paper, we use the observations from a multi-view dataset, which includes extreme ultraviolet (EUV) imaging to spectroscopy and magnetic field measurements. These data come from the Interface Region Imaging Spectrograph, the Solar Dynamics Observatory, Hinode, as well as several instruments on Solar Orbiter. RESULTS: The large temporal coverage of the region allows us to analyse the whole sequence of the filament eruption starting with its pre-eruptive state. Information given by spectropolarimetry from SDO/HMI and Solar Orbiter PHI/HRT shows that a parasitic polarity emerging underneath the filament is responsible for bringing the flux rope to an unstable state. As the flux rope erupts, Hinode EIS captures blue-shifted emission in the transition region and coronal lines in the northern leg of the flux rope prior to the flare peak. This may be revealing the unwinding of one of the flux rope legs. At the same time, Solar Orbiter SPICE captures the whole region, complementing the Doppler diagnostics of the filament eruption. Analyses of the formation and evolution of a complex set of flare ribbons and loops, of the hard and soft X-ray emissions with STIX, show that the parasitic emerging bipole plays an important role in the evolution of the flaring region. CONCLUSIONS: The extensive dataset covering this M-class flare event demonstrates how important multiple viewpoints and varied observations are in order to understand the complexity of flaring regions. While the analysed data are overall consistent with the standard flare model, the present particular magnetic configuration shows that surrounding magnetic activity such as nearby emergence needs to be taken into account to fully understand the processes at work. This filament eruption is the first to be covered from different angles by spectroscopic instruments, and provides an unprecedented diagnostic of the multi-thermal structures present before and during the flare. This complete dataset of an eruptive event showcases the capabilities of coordinated observations with the Solar Orbiter mission

Fleeting small-scale surface magnetic fields build the quiet-Sun corona

Arch-like loop structures filled with million Kelvin hot plasma form the building blocks of the quiet-Sun corona. Both high-resolution observations and magnetoconvection simulations show the ubiquitous presence of magnetic fields on the solar surface on small spatial scales of $\sim$100\,km. However, the question of how exactly these quiet-Sun coronal loops originate from the photosphere and how the magnetic energy from the surface is channeled to heat the overlying atmosphere is a long-standing puzzle. Here we report high-resolution photospheric magnetic field and coronal data acquired during the second science perihelion of Solar Orbiter that reveal a highly dynamic magnetic landscape underlying the observed quiet-Sun corona. We found that coronal loops often connect to surface regions that harbor fleeting weaker, mixed-polarity magnetic field patches structured on small spatial scales, and that coronal disturbances could emerge from these areas. We suggest that weaker magnetic fields with fluxes as low as $10^{15}$\,Mx and or those that evolve on timescales less than 5\,minutes, are crucial to understand the coronal structuring and dynamics.Comment: Accepted for publication in The Astrophysical Journal Letter

Magnetic fields inferred by Solar Orbiter: A comparison between SO/PHI-HRT and SDO/HMI

The High Resolution Telescope (HRT) of the Polarimetric and Helioseismic Imager on board the Solar Orbiter spacecraft (SO/PHI) and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) both infer the photospheric magnetic field from polarised light images. SO/PHI is the first magnetograph to move out of the Sun--Earth line and will provide unprecedented access to the Sun's poles. This provides excellent opportunities for new research wherein the magnetic field maps from both instruments are used simultaneously. We aim to compare the magnetic field maps from these two instruments and discuss any possible differences between them. We used data from both instruments obtained during Solar Orbiter's inferior conjunction on 7 March 2022. The HRT data were additionally treated for geometric distortion and degraded to the same resolution as HMI. The HMI data were re-projected to correct for the $3^{\circ}$ separation between the two observatories. SO/PHI-HRT and HMI produce remarkably similar line-of-sight magnetograms, with a slope coefficient of $0.97$, an offset below $1$ G, and a Pearson correlation coefficient of $0.97$. However, SO/PHI-HRT infers weaker line-of-sight fields for the strongest fields. As for the vector magnetic field, SO/PHI-HRT was compared to both the $720$-second and $90$-second HMI vector magnetic field: SO/PHI-HRT has a closer alignment with the $90$-second HMI vector. In the weak signal regime ($< 600$ G), SO/PHI-HRT measures stronger and more horizontal fields than HMI, very likely due to the greater noise in the SO/PHI-HRT data. In the strong field regime ($\gtrsim 600$ G), HRT infers lower field strengths but with similar inclinations (a slope of $0.92$) and azimuths (a slope of $1.02$). The slope values are from the comparison with the HMI $90$-second vector.Comment: 10 pages, 5 figures, accepted for publication in A&A; manuscript is a part of Astronomy & Astrophysics special issue: Solar Orbiter First Results (Nominal Mission Phase