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Analisi sperimentale delle prestazioni aero-termiche di canali di raffreddamento per il bordo d'uscita di pale di turbina a gas
No full textRotational effects on the flow field inside a leading edge impingement cooling passage
Full text linkThe work reports for the first time detailed experimental data about the flow field inside an advanced leading edge cooling channel for gas turbine blades. The geometry key features are multiple internal impinging jests and coolant extraction for blade film cooling protection. Measurements have been performed by means of 2D and Stereo PIV, in both static and rotating conditions, with Reynolds number of 30k and 10k and a Rotation number of 0.05, both defined with reference to the jet characteristics. Different crossflow conditions in the feeding channel have been used to simulate the three main blade regions (i.e. HUB, MID, and TIP). The flow inside the feeding channel is significantly affected by rotation, conversely, when moving inside the main impingement duct, the jet core has been found to be only marginal modified due to rotation. Finally, a substantial Reynolds number independence has been found
Evoluzione dello stato del combustibile stoccato su navi alimentate a gas naturale liquefatto
No full textLa continua attenzione verso la riduzione delle emissioni inquinanti dovute al traffico marittimo sta portando ad un sempre
maggior interesse verso l’impiego del Gas Naturale Liquefatto (GNL) come combustibile navale. Lo stoccaggio in forma
liquida richiede l’impiego di serbatoi criogenici nei quali il combustibile è soggetto ad una continua produzione di vapore
(BOG) conseguente agli inevitabili flussi termici che attraversano le pareti dei serbatoi. I principali effetti della produzione di
BOG sono la tendenza all’aumento della pressione nel serbatoio e la variazione della composizione del fluido stoccato.
Conseguentemente, per il corretto dimensionamento e gestione del sistema di trattamento del combustibile è necessario poter
prevedere le variazioni dello stato del combustibile stoccato e del quantitativo di BOG che deve essere estratto per consentire
un opportuno controllo della pressione nel serbatoio.
Nel presente lavoro vengono presentati i modelli di calcolo sviluppati per determinare: i) le variazioni della composizione e
delle proprietà del GNL, trattato come fluido multicomponente in equilibrio liquido-vapore, ii) il tasso di produzione di BOG,
e iii) l’evoluzione del methane number (potere anti-detonante) del combustibile. I modelli di calcolo sono stati applicati
all’analisi di un caso realistico, ovvero l’evoluzione dello stato del combustibile stoccato su una nave mercantile di media
stazza (33000 DWT), operante sulla rotta Dubai – Amburgo – Dubai e alimentata unicamente a GNL. I risultati evidenziano
l’importanza della presente analisi, mettendo in luce significative variazioni della portata e delle proprietà del BOG estratto dal
serbatoio durante il viaggio della nave. Inoltre la possibilità di predire le variazioni della composizione del combustibile ha
permesso di analizzare l’evoluzione del suo methane number per due diverse composizioni iniziali del GNL e al variare del
flusso termico attraverso le pareti del serbatoio
Low Reynolds number flow in rectangular cooling channels provided with low aspect ratio pin fins
No full textThe flow structures around single heat transfer promoters of different shapes (square, circular, triangular and rhomboidal) have been investigated experimentally by means of a 2-D Particle Image Velocimetry (PIV) technique. The geometrical configuration and flow conditions considered are typical of real liquid cooling channels. They include low aspect ratio pin fins confined at both ends by the walls of a rectangular channel, water flow at low Reynolds numbers (Re. =800, 1800, 2800), high core flow turbulence and undeveloped boundary layers at the position of the obstacle. In front of the pin fins the high turbulence level is found to promote a strong instability of the horseshoe vortex system that forms at the wall/obstacle junction. In particular, frequent events of break-away of the primary vortices and inrush of core fluid, which are known to enhance the wall heat transfer, are observed in the cases of square and circular pins already from Re. =1800. The near wake downstream of the obstacles appears to be influenced by streamwise oriented vortical structures produced at the wall/obstacle junction. They give rise to spanwise velocity components (up-wash flow) that lead to a three-dimensional mass recirculation behind the pins. The combination of up-wash flows, low Reynolds number and high core flow turbulence gives rise to a competition between the classical alternate vortex shedding and an irregular shedding mode characterized by the decoupling of the shear layers and the absence of well organized primary structures. At Re. =800, the irregular shedding prevails and the mean wake topology is almost insensitive to the obstacle shape. As the Reynolds number is increased, the junction flow structures reduce in size and strength, their effect on the wake flow weakens and the recirculation structures behind the obstacles differentiate significantly according to the pin shape. Besides investigating complex flow structures in geometrical and flow configurations of practical interest but scarcely covered by the current literature, the present work provides an accurate experimental data-base for the validation of CFD codes under challenging flow conditions
Buoyancy effects at high rotation number on the flow field inside a triangular shaped rib roughened channel
No full textThe flow field inside a triangular cooling channel for the leading edge of a gas turbine blade has been investigated. The efforts were focused on the interaction between effects of rotation and those induced by turbulence promoters, i.e. perpendicular square ribs placed on both leading and trailing sides of the duct. PIV and Stereo-PIV measurements have been conducted for Re=10000, rotation number of 0, 0.2, and 0.6, and buoyancy parameter equal to 0, 0.08, and 0.7. Coriolis secondary flows are detected in the duct cross section, but contrary to the smooth case, they are characterized by a single main vortex and are less affected by an increase of the rotation parameter. Moreover, their main topology is only marginally affected by the buoyancy forces. Conversely, the features of the recirculation structure downstream the ribs turned out to be more sensible to a change of the sense of rotation and to buoyancy forces
Effects of rotation and buoyancy forces on the flow field behavior inside a triangular rib roughened channel
Full text linkThe flow field inside a triangular cooling channel for the leading edge of a gas turbine blade has been investigated. The efforts were focused on the investigation of the interaction between effects of rotation, of buoyancy forces, and those induced by turbulence promoters, i.e., perpendicular square ribs placed on both leading and trailing sides of the duct. Particle image velocimetry (PIV) and stereo-PIV measurements have been performed for Re-Dh = 10(4), rotation number of 0, 0.2, and 0.6, and buoyancy parameter equal to 0, 0.08, and 0.7. Coriolis secondary flows are detected in the duct cross section, but contrary to the smooth case, they are characterized by a single main vortex and are less affected by an increase of the rotation parameter. Moreover, their main topology is only marginally sensitive to the buoyancy forces. Conversely, the features of the recirculation structure downstream the ribs turned out to be more sensitive to both the buoyancy forces and to the stabilizing/destabilizing effect on the separated shear layer induced by rotation
Flow field analysis inside a gas turbine trailing edge cooling channel under static and rotating conditions: Effect of ribs
No full textThe present work is part of a wider research program which concerns the aero-thermal characterization of cooling channels for the trailing edge of gas turbine blades. The selected passage model is characterized by a trapezoidal cross-section of high aspect-ratio and coolant discharge at the blade tip and along the wedge-shaped trailing edge, where seven elongated pedestals are also installed. In this contribution, a new channel configuration provided with inclined ribs installed inside the radial development region is analyzed, extending the previous results and completing the already available data base, thus providing an overall review of the aero-thermal performance of the considered passage. The velocity field inside the channel was measured by means of 20 and Stereo-Ply techniques in multiple flow planes under static and rotating conditions. The tests were performed under engine similar conditions with respect to both Reynolds (Re 20,000) and Rotation (Ro = 0, 0.23) numbers. Time averaged flow fields and velocity fluctuation data inside the stationary and rotating channels are analyzed and also critically compared with the data acquired without ribs. In this way the effects on the flow field induced by both rotation and ribs are clearly described. In particular, the ribs modify substantially both the flow field on the channel walls where they are installed and the 3D separation structures that surround the pedestals. If also rotation is taken into account, the relative flow field is characterized by a considerable guiding effect of the ribs coupled with a stronger flow separation on the obstacles that further enhances the heat transfer performances. This behavior was confirmed exploiting the wide thermal data base already available, obtaining a direct link between the observed flow features and the heat transfer performance
Aerodynamic behavior under rotation of an advanced leading edge impingement cooling channel
No full textA preliminary characterization of the flow field inside an advanced leading edge cooling channel characterized by multiple internal impinging jests has been carried out by means of 2D and Stereo PIV. The measurements have been conducted both in the jets impingement region and in the feeding channel. Test conditions are characterized by a Reynolds number of 30k and a Rotation number of 0.05, both values are defined with reference to the jet characteristics. Different crossflow conditions, namely feeding channel over jet flow rates ratio, have been used to simulate the three main blade regions (i.e. HUB, MID, and TIP). The flow inside the feeding channel turned out to be significantly affected by rotation, with stronger effects found at blade TIP, where the local rotation number is higher. Conversely, when moving inside the main impingement duct, the jet core has been found to be only marginal modified due to rotation. Finally, Reynolds number effect has been also investigated by repeating measurements for the MID crossflow condition at Re=10k. A substantial Reynolds number independence has been found
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