1,721,026 research outputs found
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
Performance analysis of a motor-sailing propulsion system for control design purposes
No full textThis paper presents the simulation approach developed to evaluate the interaction between sailing and motor propulsion of
a tall ship. In particular, the study is focused on the computational fluid dynamics (CFD) analysis of the wind thrust action
on the sails. CFD modelling has been used because of the lack on scientific literature of the performance assessment of a
square soft sail, especially if the interference among the several sails has to be considered. CFD results are discussed and then
properly arranged to develop a propulsion simulator, able to provide interesting information on the whole ship performance.
In sailing propulsion mode, it is worth paying attention also to the effect of the trailing propeller on the shaftline dynamics,
mainly for reasons due to the efficiency reduction of the oil lubrication system at low revolutions. The final goal of the present
work is to propose material and methods to find out and set up innovative control logics, in order to optimise the particular
motor-sailing propulsion of the tall ships
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
Experiences in the application of intermittency detection techniques to hot film signals in transitional boundary layer
No full textAnalysis of tonal noise generating mechanisms in low-speed axial-flow fans
No full textThe present paper reports a comparison of experimental SPL spectral data related to the tonal noise generated by axial-flow fans. A nine blade rotor has been operated at free discharge conditions and in four geometrical configurations in which different kinds of tonal noise generating mechanisms are present: large-scale inlet turbulent structures, tip-gap flow, turbulent wakes, and rotor-stator interaction. The measurements have been taken in a hemi-anechoic chamber at constant rotational speed and, in order to vary the acoustic source strength, during low angular acceleration, linear speed ramps. In order to avoid erroneous quantitative evaluations if the acoustic propagation effects are not considered, the acoustic response functions of the different test configurations have been computed by means of the spectral decomposition method. Then, the properties of the tonal noise generating mechanisms have been studied. To this aim, the constant-Strouhal number SPL, obtained by means of measurements taken during the speed ramps, have been compared with the propagation function. Finally, the analysis of the phase of the acoustic pressure has allowed to distinguish between random and deterministic tonal noise generating mechanisms and to collect information about the presence of important propagation effects
Installation Effects on the Tonal Noise Generated by Axial Flow Fans will be published in Journal of Sound and Vibration
No full textThe paper presents the results of experiments on a low-speed axial-flow fan flush mounted on flat panels of different size and shape which are typically employed in tests on automotive cooling fans. The experiments have been conducted in a hemi-anechoic chamber and were aimed at evaluating the installation effects of the whole test configuration, including mounting panel and chamber floor. The panel causes important attenuation in a narrow, low frequency range, which is related to the size of the panel and affects tonal noise more strongly than the broadband one. The propagation function presents an important dip at about 400 Hz and also a regular wavy trend associated to reflection from the floor.
The analysis is performed by means of an existing spectral decomposition technique and a new one, which allows to consider different noise generating mechanisms and also to separate the emitted tonal and broadband noise from the associated propagation effects. In order to better identify the features of the noise at BPF harmonics, the phase of the acoustic pressure is also analyzed.
The new technique is based on SPL spectral data measured during speed ramps, which allow obtaining both constant-Strouhal number SPL data, to which the new spectral decomposition technique may be easily applied, and constant-speed data, to which the standard spectral decomposition techniques may be applied.
Based both on the similarity theory and on the analysis of Green’s function of the problem, a theoretical description of the structure of the received noise power spectrum is given. This allows to determine the conditions under which the spectral decomposition may be performed avoiding approximations. Then, the possibility of discriminating between tonal and broadband noise generating mechanisms is analyzed and a theoretical base for the new spectral decomposition technique is provided
Aerodynamic noise from cooling and HVAC systems
No full textThe present paper deals with the aerodynamic noise
generated by cooling and HVAC systems employed in land vehicles. After a brief description of the physical origin of aerodynamic noise, the features important to system engineers dealing with fans installation and operation are considered. First, the main scaling laws useful to estimate the sound level spectrum are reported. Then, the main characteristics of the sound pressure level spectrum
are related to the typical aerodynamic generating mechanisms and to the quality of the perceived sound, and some guidelines for noise reduction are listed. Finally, a method for the employ of results obtainable from laboratory tests is proposed which aims to identify the origin of annoying fluctuations in the received noise
Un impianto sperimentale per lo studio dell’aerodinamica instazionaria di bruciatori di turbine a gas
No full textAl fine di studiare l’aerodinamica instazionaria dei combustori di turbine a gas è stata realizzata una nuova galleria del vento in grado di simulare il flusso monofase non combustivo all'interno di modelli composti da un prevorticatore ed un tubo di miscelamento.
Il flusso generato è uniforme ed a basso livello di turbolenza, e la galleria è stata inoltre dotata di strumenti di misura adatti a valutare con precisione le condizioni di funzionamento. Il posizionamento delle sonde viene effettuato mediante un sistema di movimentazione a tre assi controllato da un computer, e sono disponibili sofisticate strumentazioni di misura quali: LDA, PIV, anemometro a filo caldo ed a film caldo nonché trasduttori di pressione ad alta risposta in frequenza
Experimental Flame Front Characterisation in a Lean Premix Burner Operating with Syngas Simplified Model Fuel
No full textThe recent growing attention to energy saving and environmental protection issues has brought attention to the possibility of exploiting syngas from gasification of biomass and coal for the firing of industrial plants included in the, so called, Integrated Gasification Combined Cycle power plants. In order to improve knowledge on the employ of syngas in lean premixed turbulent flames, a large scale swirl stabilized gas-turbine burner has been operated with a simplified model of H2 enriched syngas from coal gasification. The experimental campaign has been performed at atmospheric pressure, with operating conditions derived from scaling the real gas turbines. The results are reported here and consist of OH-PLIF (OH Planar Laser Induced Fluorescence) measurements, carried out at decreasing equivalence of air/fuel ratio conditions and analysed together with the mean aerodynamic characterisation of the burner flow field in isothermal conditions obtained through LDV (Laser Doppler Velocimetry) and PIV (Particle Image Velocimetry) measurements. The OH concentration distributions have been analysed statistically in order to obtain information about the location of the most reactive zones, and an algorithm has been applied to the data in order to identify the flame fronts. In addition, the flame front locations have been successively interpreted statistically to obtain information about their main features and their dependence on the air to fuel ratio behaviour
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