1,721,027 research outputs found
A general procedure to determine the transfer matrix of Francis turbine conduits in presence of cavitating and periodically detaching flow
No full textIn present paper the equations are determined which describe small harmonic oscillation of velocity, pressure and velocity potential for low celerity flow in straight ducts with cross section arbitrarily varying in both time and space.
The obtained equations allow for the modelling of phenomena as cavitation and pulsating flow detachment.
Eventually a general procedure is given which allows for the numerical determination of the duct transfer matrix in the general case
Analysis of the SPL Spectra Generated by Axial Flow Fans Working under Similarity Conditions
No full textIn the present paper a technique based on the similarity theory is shown which is aimed to study the trailing edge noise generated by axial flow fans. Given a set of SPL data
measured on rotors of different diameter, once the analitycal structure of the SPL power spectrum is assumed, the technique allows to determine the dependence of the spectrum on the rotational speed and on the diameter. Such a technique has a general usefulness since it allows to verify the main features of measured and predicted SPL spectra. In the present case it has been developed to test trailing edge noise prediction methods and, possibly, to develop new semi-empirical correlations. After a description of the basic theory, the technique is applied to preliminary measurements taken in a hemi-anechoic chamber. The application shows that, for the present rotors, the measured OASPL follows the expected scaling law and slightly decreases as the Reynolds number is increased. Such a result needs to be confirmed by further investigations taken under more controlled inflow conditions
A Transfer Matrix Model for a Francis Turbine Group Interacting with Hydraulic Circuit and Electrical Network
No full textAn analytical transfer matrix model for a hydropower group composed by a Francis turbine, alternator, speed governor, excitation system and transmission line is presented. The model assumptions are clearly stated and the fully modular structure allows for an easy change of submodels
Un metodo di calcolo per lo studio delle oscillazioni termoacustiche in camere di combustione di turbine a gas
No full textIl presente lavoro riguarda lo studio delle proprietà trasmissive e della stabilità dei moderni combustori di turbina a gas a fiamma povera premiscelata. Con riferimento ai sistemi termoacustici, ed in particolare alle camere di combustione delle moderne turbine a gas, vengono brevemente descritte le applicazioni del metodo delle matrici di trasferimento e della teoria della stabilità per i sistemi lineari. Quindi viene descritto un codice di calcolo che implementa tale teoria ed infine mostrati i risultati di alcuni calcoli di validazione effettuati con lo stesso su diversi test-cases di differente complessità
Design of Off-statistics Axial-flow Fans by Means of Vortex Law Optimization
No full textOff-statistics input data sets are common in axial-flow fans design and may easily result in some violation of the requirements of a good aerodynamic blade design. In order to circumvent this problem, in the present paper, a solution to the radial equilibrium equation is found which minimizes the outlet kinetic energy and fulfills the aerodynamic constraints, thus ensuring that the resulting blade has acceptable aerodynamic performance. The presented method is based on the optimization of a three-parameters vortex law and of the meridional channel size. The aerodynamic quantities to be employed as constraints are individuated and their suitable ranges of variation are proposed. The method is validated by means of a design with critical input data values and CFD analysis. Then, by means of systematic computations with different input data sets, some correlations and charts are obtained which are analogous to classic correlations based on statistical investigations on existing machines. Such new correlations help size a fan of given characteristics as well as study the feasibility of a given design
Transfer Matrix Modelling of Hydraulic Machinery Components at High Mach Number Due to Cavitation
No full textA transfer matrix model for cylindrical and conical ducts is presented which allows to take into account the low Mach number due to cavitation. For the cylindrical duct an analytical solution exists, while for the conical duct an approximate solution has been found by means of the method of characteristics. The latter has been validated by means of the numerical integration of the differential equation of the model. The model may be employed for the draft tube of Francis turbines in presence of cavitating vortex rope
Spectral decomposition of the aerodynamic noise generated by rotating sources
No full textA method is posed for separating the noise emitted by an aerodynamic source from
propagation effects using spectral decomposition. This technique is applied to the
power spectra of a fan measured at several rotational speeds. Although it has been
conceived for rotating sources as turbomachinery rotors, the method may be easily
applied to low speed stationary sources such as jets and flows in stators and about
isolated airfoils.
Based on the similarity theory, a clear description of the structure of the power
spectrum of the received noise is given and the effect of rotational speed variations is
considered as a means to obtain a data set suitable to perform the spectral
decomposition. The problem is analyzed in order to clarify possibilities and limitations
of the method and then an algorithm is presented which is based on the solution of the
derived equations. Particular care is devoted to both the numerical details and the
operative aspects.
The validation of the algorithm is performed by means of numerically generated
input data. Next, in order to verify the ability of the method in separating scattered from
emitted sound, an automotive cooling fan has been tested in the DIMSET hemi-anechoic
room in a free-field configuration and with a shielded microphone. These two
apparently distinct spectra collapse to within less than 2 dB after the spectral
decomposition has been performed. The tests prove the ability of the method despite
the modest quantity of input data
Interazione scia-strato limite sulle pale del diffusore di uno stadio centrifugo
No full textNel presente lavoro vengono presentati i risultati di misure del campo di velocità a valle di un modello di elica medio-veloce per propulsione navale effettuate mediante anemometro laser-Doppler nel tunnel di cavitazione dell’Università di Genova. Le misure presentate sono state effettuate in corrispondenza di diversi piani normali all’asse di rotazione nonché su superfici cilindriche di differente raggio e sono relative al punto di funzionamento nominale (coefficiente di avanzo J = 0.95). Il campo di moto nel sistema di riferimento relativo (in termini di velocità media e turbolenza) viene ricostruito mediante la tecnica della media di insieme. Il carattere quantitativo dei risultati, insieme con la loro completezza e con le stime degli errori di misura, li rende particolarmente utili non solo per una migliore conoscenza del fenomeno fisico, ma anche per la validazione dei metodi di progetto ed analisi
Effect of the rotor-stator gap variation on the tonal noise generated by axial-flow fans
No full textStudio sperimentale del flusso attorno ad un’elica per propulsione navale
No full textNel presente lavoro vengono presentati i risultati di misure del campo di velocità a valle di
un modello di elica medio-veloce per propulsione navale effettuate mediante anemometro laser-
Doppler nel tunnel di cavitazione dell’Università di Genova.
Le misure presentate sono state effettuate in corrispondenza di diversi piani normali all’asse
di rotazione nonché su superfici cilindriche di differente raggio e sono relative al punto di
funzionamento nominale (coefficiente di avanzo J = 0.95). Il campo di moto nel sistema di
riferimento relativo (in termini di velocità media e turbolenza) viene ricostruito mediante la tecnica
della media di insieme.
Il carattere quantitativo dei risultati, insieme con la loro completezza e con le stime degli
errori di misura, li rende particolarmente utili non solo per una migliore conoscenza del fenomeno
fisico, ma anche per la validazione dei metodi di progetto ed analisi
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