1,720,978 research outputs found
Combined heat transfer and flow fields analysis in rib-roughened cooling passages for turbine blades
No full textThe present study deals with a detailed experimental investigation of the turbulent flow inside a rib-roughened turbine blade cooling channel. The measurements are carried out by means of a 2D PIV technique in a stationary straight channel with 10% blockage ribs installed on one wall. They constitute the necessary complement to the already available heat transfer data. The present aerodynamic results are compared with available data on a similar channel but with a blockage ratio of 30 %. The main objective is to deepen the analysis and enhance the understanding of this complex flow field, particularly with respect to the definition of a mean flow model and to its aero-thermal characteristics. More precisely, the stream-wise/normal to the wall component of the Reynolds stress tensor is shown to be closely related to the heat transfer rate on the channel surfaces. A correlation to estimate the heat transfer field from the aerodynamic data, previously obtained for the high blockage rib roughened channel flow, is validated for this 10% blockage configuration
Validation of the transient liquid crystal thermography technique for heat transfer measurements on a rotating cooling passage
Full text linkThe transient liquid crystal thermography can be a suitable tool to study heat‐transfer performances on internal cooling schemes of gas turbine blades. One of the hot topics related to this methodology is about the level of reliability of the heat‐transfer assessments in rotating tests where the fluid experiences time‐dependent rotating effects. The present study contribution aims to experimentally validate by cross‐comparison of the outcomes obtained by employing the transient technique with those from the steady‐state liquid crystal thermography in which the rotational effects occur as time‐stable by definition. Heat‐transfer measurements have been conducted on a rib‐roughened square cross‐section channel, with an inlet Reynolds number equal to 20,000 and rotation number up to 0.2. Special attention has been paid to the definition of the more reliable calibration strategy for liquid crystals that are employed in the transient thermography and to the proper estimation of the heat losses in the post‐processing of the steady‐state experimental data. The results show great accordance between the indications provided by the two techniques both in static and rotating conditions, demonstrating the possibility to exploit the advantages of the transient liquid crystal thermography for the investigation of heat transfer into rotating cooling channels
Culture europee e tradizione latina. Atti del Convegno Internazionale di studi Cividale del Fiuli, Fondazione Niccolò Canussio, 16-17 Novembre 2001
No full textHeat transfer characterization inside a rotating rib roughened cooling channel with multiple heated walls
No full textThis work experimentally investigates the effects of walls heating conditions on the heat transfer coefficient distribution inside a rotating cooling channel. The model has a square cross-section with a hydraulic diameter of 50 mm and one ribbed side. The ribs are perpendicular to the main flow direction, the rib pitch-to-height ratio is 10, and the blockage ratio is 10%. Detailed heat transfer measurements were performed employing the liquid crystals thermography in steady-state approach under two thermal boundary conditions: only ribbed wall heated or equal heat fluxes set to ribbed wall and sidewalls. Inlet Reynolds number was 20000 and the tests were conducted in both static and rotating conditions up to a rotation number of 0.18, with the ribbed wall acting as trailing edge side. The results show that the wall heating conditions have a negligible effect on the heat transfer distribution for the stationary case, whereas, they lead to a modification of the heat transfer distribution under rotation with an overall enhancement when three walls are heated
An efficient numerical model of pulsating combustion and its experimental validation
No full textA simple and efficient numerical model is presented for the simulation of pulse combustors. It is based on the numerical solution of the quasi-1D unsteady flow equations and on phenomenological sub-models of turbulence and combustion. The gas dynamics equations are solved by using the Flux Difference Splitting (FDS) technique, a finite-volume upwind numerical scheme, and ENO reconstructions to obtain second order accurate non-oscillatory solutions. The numerical fluxes computed at the cell interfaces are used to transport also the reacting species, their formation energy and the turbulent kinetic energy. The combustion progress in each cell is evaluated explicitly at the end of each time step according to a second-order overall reaction kinetics. In this way, the computations of gas dynamic evolution and heat release are decoupled, which makes the model particularly simple and efficient. A comprehensive set of measurements has been performed on a small Helmholtz type pulse-jet in order to validate the model. Air and fuel consumptions, wall temperatures, pressure cycles in both combustion chamber and tail-pipe, and instantaneous thrust have been recorded in different operating conditions of the device. The comparison between numerical and experimental results turns out to be satisfactory in all the working conditions of the pulse-jet. In particular, accurate predictions are obtained of the device operating frequency and of shape, amplitude and phase of the pressure waves in both combustion chamber and tail-pipe
Comparison of Rankine cycles for micro-chp generation based on inward flow radial turbine or scroll expander
No full textThis contribution aims to analyze micro-CHP units based on Rankine cycles. Two types of expander are considered: a small scale inward flow radial turbine and a volumetric scroll type expander. This latter, should allow to overcome the limitation imposed by a standard steam-turbine that arise when the required shaft-power is very low. Moreover, the scroll expander will also allow to easily treat wet steams, which must be avoided when considering a turbo-expander.
The final aim is to deduce which one of the two types of
expander is more suitable, with a specified target performance
and the availability of a certain hot source. In order to define
the thermodynamic expansion process, the analysis uses a onedimensional model of the radial turbine, previously developed
by the authors, and of an estimation of the scroll expander efficiency. Also, the analysis is carried out for different working
fluids, such as water, and two organic fluids, cyclohexane and
toluene.
Through the discussion of the results, for a specified set of constraints (e.g. expander inlet temperature, temperature of
condensation, expander geometrical parameters) it is possible
to deduce important indications on the most suitable expander
for a given cycle layout
La strategia del ragno, ovvero la rivincita di Aracne. Fortuna tardo-antica (Sidonio Apollinare, Claudiano) di un mito ovidiano
No full textL'etimologia di aletheia e la concezione platonica della verità
No full textDiscussione dell'etimologia heideggeriana di aletheia in relazione a testi greci antichi e della concezione ontologica della verità in Platon
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
- …
