International and National Journals
G. Cignolo, F. Alasia, A. Capelli, R. Goria, G. La Piana
A primary standard piston prover for measurement of very small gas flows: an update
Sensor Review, Emerald Group Publ. Ltd, Addingham (UK), vol. 25, no. 1, pp. 40-45, 2005.
A high-accuracy prover is described, which is the Italian national standard for gas flow rates, now upgraded for measurements in the range 0.1 mL/min to 2 L/min. The prover (full capacity: 3 liters) measures volume changes implemented by means of a motor-operated piston (120 mm dia.) which is introduced into (or extracted out of) a temperature-controlled (± 10 mK) chamber containing the working gas at near ambient conditions. The prover can either deliver or collect measured gas flows, depending upon the type of instrument to which it is connected; piston displacements are measured by means of a laser interferometer. Motor speed is controlled in such a way that gas delivery is made at constant rate, whereas variable incoming gas flows can be measured at constant pressure. Owing to the accurate measurement of temperatures and pressures, the mass flow rate of pure gases can be inferred to practically the same high accuracy as the volume flow rate (relative standard uncertainty: 0.013% to 0.03%).
W. Bich, R. Goria
Kilogrammo, una questione di peso
Tutto Scienze e Tecnologia, La Stampa, Torino, n. 1184, p. 1, 15 giugno 2005.
Pubblicazione divulgativa sulle nuove proposte di ridefinizione dell'unità di massa mediante la costante di Avogadro o la costante di Planck.
G. Cignolo
EUROMET, promuovere l'accettazione reciproca delle misure
EIDOS, la Rivista del Metering, n. 3, pp. 5-8, 2005.
EUROMET purpose, structure and activities are briefly outlined for readers of a magazine devoted to Metering, namely the measurement of water, natural gas, heat and electricity carried out by utilities delivering such goods to users. In this framework, a report is given of the annual meeting of the EUROMET TC Flow held in Greece in March 2005, where current joint research projects and comparisons of measurement standards have been reviewed and more projects where launched in the field of technical and/or custody transfer measurement of water, liquid hydrocarbons, air and natural gas.
W. Bich
L'incertezza nemica del dubbio
Unificazione e certificazione, n. 8, pp. 42-44, 2005.
Articolo divulgativo sugli sviluppi recenti nel campo dell'incertezza di misura.
Conference Proceedings
P.G. Spazzini, R. Arina, A. Rivetti, P.F. Siciliano
Numerical prediction of internal supersonic flow in a regulation valve for low-thrust space engines
IMACS 2005, Paris (France), July 2005 (on cd rom).
This work deals with the numerical prediction of the unsteady flow field developing in a regulation valve for space thrusters. The flow field displays an unsteady behavior characterized by complex flow patterns, because such valves have a very narrow throat and because of the presence of geometrical slope discontinuities downstream the throat for design constraints. The narrowness of the throat induces strong flow accelerations and therefore strong temperature and pressure reductions. The geometrical discontinuities cause the occurrence of local flow separations and shock waves, with an high degree of unsteadiness. Experiments have pointed out how the degree of unsteadiness strongly depends upon the nature of the gas feeding the valve. The strongest unsteadiness has been observed in the case of xenon at low exit pressures. Numerical simulations, using a compressible Navier-Stokes flow solver, have been performed under different working conditions and for two different gases, nitrogen and xenon. The results agree with experiments, and provide details of the unsteadiness mechanism and of its evolution depending upon the operating conditions.
R. Arina
Numerical method for the convected Lighthill's equation
11th AIAA/CEAS Aeroacoustics Conference, Monterey (California, USA), AIAA Paper 2005-2028, May 2005.
The aim of the present work is to extend a numerical technique, developed for the solution of the original Lighthill's wave equation, to the convected wave equation valid for nonuniform mean flows. Assuming harmonic time dependence, the convected wave equation is solved in the frequency domain on unstructured mesh. For each wave number, an associated convected Helmholtz problem, with the corresponding inhomogeneous forcing term, is solved. The main advantages with respect to existing techniques (such as GFD) is the ability of dealing with generally shaped boundaries. Moreover, the frequency-domain discretization approach makes possible to treat each wave number separately. This property is particularly useful for design optimization calculation. Preliminary results for a test model and a turbofan engine configuration are presented.
G.M. Di Cicca, G. Iuso
On a yawed synthetic jet - Turbulent boundary layer interaction
6th International Symposium on Particle Image Velocimetry, paper 0117, Pasadena (California, USA), September 2005.
Digital Particle Image Velocimetry has been applied to the study of a flat plate turbulent boundary layer interacting with a 2D synthetic jet. Changes in the mean flow field have been analyzed for different yaw angles of the synthetic jet slit and for different actuation frequencies. A particular attention has been devoted to characterize the flow structure evolution downstream the suction/blowing section. The measurements showed that when the synthetic jet slit is aligned with the mean flow (β=0°) a counter-rotating vortex pair completely embedded in the boundary layer is observed. Increasing the yaw angle only one of the two shear layers producing the vortex pair is intensified by the mean flow. For a fixed yaw angle, decreasing the actuation frequency the size of the streamwise vortices appears to be diminuished as result of the reduced penetration depth of the jet. The effects of the slit orientation and of the forcing frequency also showed a great influence on the mean velocity profiles as well as on the streamwise and wall normal fluctuations and on the Reynolds shear stresses. For appropriate slit orientations and forcing frequencies specific zones of the near wall region showed reduced mean velocity gradients and velocity fluctuations.
G. Iuso, G.M. Di Cicca, R. Donelli
Flow field development of an axisymmetric synthetic jet
XVII Congresso AIMeTA Meccanica Teorica e Applicata, Firenze (Italy), settembre 2005.
The flow field development generated by a round synthetic jet has been experimentally investigated. A piston actuator system has been used to generate the synthetic jet, namely the engineof an airplane model constitutes the heart of the actuator, driven by a stepper motor. By means of hot wire anemometry technique, mean streamwise velocity and turbulent fluctuations profiles have been evaluated at different distances from the jet exit section. The jet width growth along the jet axis was also calculated. Triple decomposition has been applied to the velocity signal in order to extract the single contributions, random, coherent and mean part, to the total instantaneous velocity. The study shows that synthetic jet is characterized by common features with a continuous turbulent jet but at the same time also differences are evidenced. Synthetic jet presents in the far field self-similarity behaviour of the mean velocity profiles for shorter distances respect to a continuous turbulent jet.
G. Iuso, G.M. Di Cicca
Wall turbulence control by means of synthetic jets
XVIII Congresso Nazionale AIDAA, Volterra (Italy), settembre 2005.
An application of synthetic jets to the control of a fully developed turbulent channel flow is presented. The configuration of the synthetic jets is arranged in such a way that their interaction with the channel flow gives rise to large scale longitudinal vortical structures. These large scale structures produce reductions of both mean skin friction and root mean square of the turbulent fluctuations on both walls of the channel. These effects are persistent over a long distance from the injection points up to 43 half channel height. Despite of the unsteadiness of the injected synthetic jets the effect is that of a wall turbulence attenuation. The main mechanism affected by the interaction seems related with the regeneration of the wall turbulence and a weakening of the dominant near wall structures, low speed streaks and streamwise vortices, takes place.
G. Di Cicca, G. Iuso
Turbulent boundary layer interaction with a yawed synthetic jet
XVIII Congresso Nazionale AIDAA, Volterra (Italy), settembre 2005.
Digital Particle Image Velocimetry has been applied to the study of a flat plate turbulent boundary layer interacting with a 2D synthetic jet. Changes in the mean flow field have been analyzed for different yaw angles of the synthetic jet slit. A particular attention has been devoted to characterize the flow structure evolution downstream the suction/blowing section. The measurements showed that when the synthetic jet slit is aligned with the mean flow (β=0°) a counterrotating vortex pair completely embedded in the boundary layer is observed. Increasing the yaw angle only one of the two shear layers producing the vortex pair is intensified by the mean flow.
S. Lorefice, A. Malengo
Caratterizzazione di un materiale di riferimento per le misure della densità dei liquidi
Atti del IV Congresso Metrologia e Qualità, pp. 77-80, Torino, febbraio 2005.
I materiali di riferimento certificati sono indispensabili per la taratura di strumenti e per la validazione di metodi di misura nel campo delle proprietà fisico chimiche. Nella misura della densità dei liquidi, strumenti a tubo vibrante con risoluzioni di 0,001 kg/m3 e riproducibilità di circa 0,005 kg/m3, possono garantire misure accurate solo nell'intorno del valore di densità a cui sono tarati. Oltre ai due punti di taratura normalmente utilizzati come riferimento, corrispondenti alla densità dell'aria e quella dell'acqua, è quindi consigliabile aggiungere altri punti di densità nota su cui caratterizzare lo strumento. Un liquido particolarmente adatto a questo scopo è l'idrocarburo n-nonano (C9H20) il quale ha una densità intermedia tra quella dell'acqua e quella dell'aria. Allo scopo di caratterizzare questo liquido come materiale di riferimento certificato, l'IMGC ne ha verificato l'omogeneità e la stabilità della densità per un periodo di un anno, utilizzando n-nonano con due diversi gradi di purezza, al 95% e al 99,7%. I campioni sono stati conservati a diverse temperature comprese tra -10 °C e 40 °C. La misura della densità del liquido è avvenuta con periodicità trimestrale utilizzando un densimetro a tubo vibrante con risoluzione di 0,001 kg/m3 e con riproducibilità di 0,010 kg/m3. Sono state inoltre eseguite analisi gascromatografiche e di spettrometria di massa al fine di valutare le impurezze presenti e le eventuali variazioni della composizione chimica del liquido. Dai risultati ottenuti il liquido n-nonano con purezza 99,7% si è dimostrato il più adatto ad essere impiegato come materiale di riferimento certificato rispetto all' n-nonano 95%. Attualmente l'IMGC prepara e certifica materiali di riferimento certificati con l' n-nonano al 99,7%, misurando la densità a di verse temperature per mezzo di un metodo assoluto, il quale consiste nella pesata idrostatica di una sfera in zerodur riferibile al campione nazionale di densità. Dalle misure ottenute è inoltre determinata l'equazione della densità nel campo di temperatura tra 15 °C e 40 °C e la relativa incertezza di misura.
Technical Reports
G. Cignolo
Key Comparison CCM.FF-K4 - IMGC measurements on three 20 L capacity pipettes, transfer standards of the quantity: Volume of Water
IMGC Technical Report no. 126, January 2005.
Actions taken and measurement results obtained at the IMGC during the mentioned Key Comparison are described. This part of the KC consisted in measurement of the volume of water delivered at 20 °C by three standard tanks or pipettes of the nominal capacity of 20 L, designed and constructed by the pilot laboratory CENAM (Mexico) according to a novel and very performing design, that allows to finish their inside surfaces to a mirror quality. This, in turn, makes it possible to drain water almost completely and produces an excellent repeatability of the delivered volume of water. The pipettes are made of two conical pieces, connected to each other at their maximum diameter by means of massive flanges, whose front surfaces are coupled without using any gasket; thanks to their excellent surface finish, no water leakage occurs. The expanded measurement uncertainties attached to the IMGC measurement results are close to 0.3 mL, namely 0.0015%.
A. Peuto, S. Pettorruso
Final report on the measurements of mass, volume and density of Zerodur spheres Z01 and Z02 at the Istituto di Metrologia "G. Colonnetti".
IMGC Technical Report no. 128, January 2005.
In 2002 the Centro Nacional de Metrología (CENAM - Quéretaro, Mexico) and the Istituto di Metrologia "G. Colonnetti" (IMGC - Torino, Italia) agreed upon the calibration at IMGC of two volume-density standards of CENAM. The present report describes the measurements performed at the IMGC of the mass, volume and density of the standards Z01 and Z02, property of the CENAM. The present report completes and corrects the Preliminary Report (IMGC Technical Report n. 125) after the re-calibration of the additive masses used in the experiment. The uncertainties of mass and volume measurements are lower than 60 µg and 80 · 10-6 cm-3 respectively. The estimated uncertainty does not take into account the doubts recently raised on the reliability of IMGC reference standard by discrepant results obtained at other NMIs.
G. Cignolo
Research activities of the IMGC-CNR Fluid Flow group - A report to CCM WG Fluid Flow
IMGC Technical Report no. 130, February 2005.
The main activities of metrological research carried out so far by IMGC in the field of: fluid volume; liquid and gas flowrate; flow measurement of cryogenic fluids; anemometry; are reviewed for presentation to the CCM Working Group Fluid Flow, upon their request. The work carried out since the mid 1970's consists of: design, construction and characterization of novel measurement standards; construction and testing of flow transducers; participation in a large number of international comparisons of measurement standards and instruments. An extensive list of internationally published papers and of European or Key comparisons in which the IMGC was (or still is) participating is given.
F. Pennecchi, W. Bich
EUROMET.M.M-K2 key comparison. Evaluation of results
IMGC Technical Report no. 134, September 2005.
This report describes the evaluation of the results of the EUROMET.M.MK2 key comparison. The median is adopted as the key comparison reference value. The correlations existing between the individual results and the reference value are taken into account in the degrees of equivalence by using the theory of order statistics. This method provides credible uncertainties in the degrees of equivalence, thus avoiding their broadening caused by neglection of correlations.
A. Peuto, S. Pettorruso, G. La Piana, R. Goria
Le misure di volume e densità di campioni solidi all'Istituto di Metrologia "G. Colonnetti": problemi di compatibilità e riproducibilità
Rapporto Tecnico IMGC n. 144, 2005.
Negli ultimi tre anni sono sorti due gravi problemi nel campo delle misure di densità di solidi all'Istituto di Metrologia "G. Colonnetti" (IMGC): una significativa discrepanza con le misure effettuate al Phisykalisch-Technische Bundesanstalt (PTB - Germania) ed una scarsa riproducibilità dei risultati in confronti internazionali. Indagando sulle cause dei problemi, queste sono state individuate nella incompatibilità dei campioni solidi di riferimento e nella peggiorata non-linearità della bilancia, nascosta da una apparente ripetibilità delle misure. Una nuova bilancia è stata acquistata ed installata, ed è stata completamente automatizzata ed attrezzata per le pesate idrostatiche. Sono stati ripetuti numerosi confronti fra campioni, coinvolgendo anche campioni del National Metrology Institute of Japan (NMIJ - Giappone) e campioni tarati al PTB. I risultati ottenuti con il nuovo strumento risolvono il problema di riproducibilità delle misure e confermano la discrepanza fra campioni di riferimento. Non potendo al momento ripetere le misure dimensionali interferometriche del nostro campione, l'IMGC adotta temporaneamente un campione solido tarato nel 2005 al PTB.