1,721,025 research outputs found
Manufatti litici dalle ricerche 2013. Aspetti tipologici e petroarcheometrici.
No full textLa presenza di manufatti litici tra i materiali archeologici rinvenuti in gran quantità. nella grotta . un fatto noto sin dagli scavi di fine Ottocento. E’ in particolare Paolo Carucci che dedica a tali reperti la maggiore attenzione, presentandone una rassegna significativa dei vari tipi nella sua opera La Grotta Preistorica di Pertosa (Salerno), edita nel 1907. Fino alle ricerche moderne, tuttavia, poco o niente era stato accertato circa la caratterizzazione petrografica e la provenienza geografica delle rocce che compongono questi materiali. Un primo lavoro in tal senso è appunto quello esposto nel presente lavoro, riguardante un lotto di reperti acquisiti nel corso della campagna di ricerche del 2013. Lo studio di tali manufatti (perlopiù macine e pestelli), su cui sono stati fatti dei minimi prelievi invasivi tramite microcarotaggi, ha permesso la realizzazione di sezioni sottili, da osservare in microscopia ottica in luce polarizzata, e di alcuni provini in polvere, per le analisi chimiche mediante fluorescenza di raggi X. L’analisi petrografica ha permesso di identificare otto rocce sedimentarie, una roccia metamorfica e sei rocce magmatiche. Le rocce sedimentarie sono quarzareniti, arenarie miste, una litarenite e un calcare; tali litologie fanno ritenere che la loro provenienza sia riferibile a litotipi molto comuninell’Appennino meridionale con l’eccezione del calcare che potrebbe provenire dalla grotta stessa o da affioramenti limitrofi ad essa. L’unico campione di roccia metamorfica è una fillade assai probabilmente di provenienza calabrese. Le magmatiti sono due rocce intrusive e quattro rocce effusive: le rocce intrusive sono un granito a due miche e una peridotite, probabilmente entrambe di provenienza calabrese; le rocce effusive, in base alle loro caratteristiche petrografiche e chimiche, sono classificabili in parte come basaniti provenienti dal Vulture (due campioni) e in parte come fonotefriti provenienti dal Somma-Vesuvio (altri due campioni).Since the late nineteenth century excavations in the cave, it is known that there are large quantities of lithic artifacts among the archaeological finds. Paolo Carucci, in particular, devoted the most attention to these findings, showing a significant presentation of the various types of found artefacts in his book La Grotta Preistorica di Pertosa (Salerno), published in 1907. Until the beginning of modern research, however, little or nothing was known about the Petrographic characterization and the provenance of the rocks that make up these objects. The present paper is an early work in this direction, involving a sample acquired during a research campaign in 2013. Micro-cores have been taken from these artifacts (mostly querns and pestles) using minimally invasive techniques. Thin sections have been obtained from some cores, then observed in optical microscopy in polarized light, while from others artifacts powder samples have been taken for chemical analysis through X-ray fluorescence. The petrographic analysis has carried out the identification of eight sedimentary rocks, one metamorphic rock and six magmatic rocks. The sedimentary rocks are quartzarenites, mixed arenites, a litharenite and a limestone;these rock types are very common in the southern Apennines (from where presumably they come), while the limestone could belong to the cave itself or to neighboring outcrops. The only metamorphic rock found is a phyllite, most probably coming from Calabria. There are two intrusive and four effusive magmatic rocks: the intrusive ones are a two-mica granite and a peridotite, probably both belonging to Calabrian formations; the effusive rocks, according to their petrographic and chemical characteristics, are classified as basanites from Vulture (two samples) and as phonotephrites from the Somma-Vesuvius (two other samples)
Caratterizzazione archeologica e petrografica di manufatti neolitici dalla grotta di Santa Barbara (Polignano a Mare, Bari)
No full textLe ricerche effettuate nella Grotta di Santa Barbara hanno portato al rinvenimento di diverse categorie di manufatti litici, realizzati lavorando materie prime acquisite in ambiti territoriali relativamente prossimi alla cavità e, più spesso, anche molto lontani da essa. Se l’industria litica in ossidiana è molto ben attestata, lo è anche quella che predilige l’uso di calcare e calcarenite per la fabbricazione di particolari oggetti (ciondoli e lucerne).
L’arenaria, d’altro canto, mostra di essere impiegata oltre che per supporti atti alla macinazione e per talune placche, anche per singolari utensili di uso non perfettamente definibile. La presenza, infine, di oggetti miniaturistici ricavati da rocce esotiche (accettine levigate e un vago forato) sottolinea i rapporti dei gruppi umani che frequentarono la cavità con aree e popolazioni situate a distanze anche ragguardevoli, lontane centinaia di chilometri dalla Puglia centrale.Research conducted in Grotta di Santa Barbara has led to the find of different categories of lithic artefacts, made by working raw materials acquired in places relatively close to the cavity or more often very far from it. The obsidian lithic industry is very well attested, as well as one which prefers the use of limestone and calcarenite for the production of particular objects (pendants and lamps). On the other hand, sandstone appears to be used not only for making grinding tools and some plaques, but also for unusual implements whose utilization is not perfectly definable. Finally, the presence of miniature objects made from exotic rocks (polished hatchets and a perforated bead) stresses the relationship between human groups who frequented the cavity and areas and populations located even at considerable distance, hundreds of kilometres far from central Apulia
Uncertainty propagation in field inversion for turbulence modelling in turbomachinery
No full textThe simulation of turbulent flows in turbomachinery requires to describe a wide range of scales and non-linear phenomena. Since the cost of scale resolving simulations is prohibitive for several configurations, turbulence closure models are still widely used in the framework of Reynolds-averaged Navier-Stokes (RANS) equations. In order to improve the prediction capability of these models, several machine learning strategies have been proposed. Among them, the field inversion approach allows to find a correction field which can be applied to the source term of the turbulence model in order to match experimental data: the correction field can then be generalised and expressed as a function of some flow features in order to extract modelling knowledge from the data.However, the reference experimental data are affected by uncertainty and this propagates to the correction field and to the final data-augmented model. In this work, the uncertainty propagation from the reference experimental data to the correction field is investigated. In particular, the flow field around a low pressure gas turbine cascade is studied in a challenging working condition characterised by laminar separation and transition to turbulence. The original RANS results are improved by the application of the field inversion algorithm in which the required gradients are computed by means of an adjoint approach. A sensitivity analysis is performed in order to provide a linearised propagation of the uncertainty from the experimental wall isentropic Mach number to the correction field
RANS simulation of secondary flows in a low pressure turbine cascade: Influence of inlet boundary layer profile
Full text linkSecondary flows have a huge impact on losses generation in modern low pressure gas turbines (LPTs). At design point, the interaction of the blade profile with the end-wall boundary layer is responsible for up to 40% of total losses. Therefore, predicting accurately the end-wall flow field in a LPT is extremely important in the industrial design phase. Since the inlet boundary layer profile is one of the factors which most affects the evolution of secondary flows, the first main objective of the present work is to investigate the impact of two different inlet conditions on the end-wall flow field of the T106A, a well known LPT cascade. The first condition, labeled in the paper as C1, is represented by uniform conditions at the inlet plane and the second, C2, by a flow characterized by a defined inlet boundary layer profile. The code used for the simulations is based on the Discontinuous Galerkin (DG) formulation and solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Spalart Allmaras turbulence model. Secondly, this work aims at estimating the influence of viscosity and turbulence on the T106A end-wall flow field. In order to do so, RANS results are compared with those obtained from an inviscid simulation with a prescribed inlet total pressure profile, which mimics a boundary layer. A comparison between C1 and C2 results highlights an influence of secondary flows on the flow field up to a significant distance from the end-wall. In particular, the C2 end-wall flow field appears to be characterized by greater over turning and under turning angles and higher total pressure losses. Furthermore, the C2 simulated flow field shows good agreement with experimental and numerical data available in literature. The C2 and inviscid Euler computed flow fields, although globally comparable, present evident differences. The cascade passage simulated with inviscid flow is mainly dominated by a single large and homogeneous vortex structure, less stretched in the spanwise direction and closer to the end-wall than vortical structures computed by compressible flow simulation. It is reasonable, then, asserting that for the chosen test case a great part of the secondary flows details is strongly dependent on viscous phenomena and turbulence
A Numerical Smith Diagram Revision for Modern Low Pressure Turbine Profiles
No full textSmith diagram is historically one of the standard tools used
for turbine design, especially in concept design phase (CD) and
for assessment/comparison of turbine configurations. For each
turbomachinery stage, this graph provides a relation among
stage loading factor (y), flow coefficient (f) and aerodynamic
performance (). However, various essential inputs such as
stage reactions (R), aspect ratios (AR) or Reynolds numbers
(Re), or outputs like flow deflections (d), profile weights and
stresses are not directly taken into account.
In the work here presented, traditional loss correlation
models (Craig & Cox (C&C) and Ainley & Mathieson, Dunham
& Came, Kacker & Okapuu (AMDCKO)), are used to evaluate
stage performance and then to derive a more complete vision of
key parameters. Starting from a representative turbine
configuration, once some main characteristic boundary
conditions (BC) have been defined, few parameters are changed
in order to obtain a stage operating in a specific region of the
Smith diagram. By this way, it has been possible to compare
experimental data from original Smith with computational
results obtained with such approach. Moreover, additional
details previously missing (both aerodynamic and mechanical)
have been obtained and optimal design considerations have
been investigated under a multidisciplinary point of view.
In addiction, by means of dedicated tools, blade geometries
have been prepared for some of these configurations. Some
preliminary CFD 3D analyses have then been run to improve
specific understandings.
This research leads to extend Smith diagram with many
other important information for turbine module design and to
numerically revise the diagram itself, adjusting it with data
coming from modern high performance profile’s analyses
Simulation of secondary flows in turbomachinery by the discontinuous Galerkin method
Full text linkSecondary flows have a huge impact on the losses in low pressure gas turbines and the inlet boundary layer state is one of the factors which most affects the endwall flow field. The present work aims at investigating secondary flows in a low-pressure gas turbine cascade by means of RANS simulations for two different inlet conditions. The equations are discretised in space by the Discontinuous Galerkin method and implicit time integration is adopted. Changes in the peculiarities of the flow field within the cascade passage are discussed. The results are compared with experimental and numerical data available in the literature
Adaptive CFD schemes for aerospace propulsion
Full text linkThe flow fields which can be observed inside several components of aerospace propulsion systems are characterised by the presence of very localised phenomena (boundary layers, shock waves,...) which can deeply influence the performances of the system. In order to accurately evaluate these effects by means of Computational Fluid Dynamics (CFD) simulations, it is necessary to locally refine the computational mesh. In this way the degrees of freedom related to the discretisation are focused in the most interesting regions and the computational cost of the simulation remains acceptable. In the present work, a discontinuous Galerkin (DG) discretisation is used to numerically solve the equations which describe the flow field. The local nature of the DG reconstruction makes it possible to efficiently exploit several adaptive schemes in which the size of the elements (h-adaptivity) and the order of reconstruction (p-adaptivity) are locally changed. After a review of the main adaptation criteria, some examples related to compressible flows in turbomachinery are presented. An hybrid hp-adaptive algorithm is also proposed and compared with a standard h-adaptive scheme in terms of computational efficiency
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
FIELD INVERSION AND MACHINE LEARNING STRATEGIES FOR IMPROVING RANS MODELLING IN TURBOMACHINERY
Full text linkTurbulence and transition modelling are critical aspects in the prediction of the flow field in turbomachinery. Recently, several research efforts have been devoted to the use of machine learning techniques for improving Reynolds-averaged Navier-Stokes (RANS) models. In this framework, a promising technique is represented by field inversion which requires to find an optimal correction field that minimises the error between numerical predictions and experimental data. In this work, Artificial Neural Networks and Random Forests are investigated as tools to generalise the correction provided by field inversion. An approach to automatically identify the regions where the correction model should be computed is proposed: this improves the fitting and reduces the calls to the model during the predictions. Furthermore, a correction-based weighting of the database is introduced in order to improve the training performances. The potential and the issues of the methods are investigated on a high-lift gas turbine cascade at low Reynolds number
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