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Experimental analysis on the noise of propellers for small uav
No full textMain goal of this paper is an experimental analysis on the aeroacoustic features of propellers aimed at the propulsion of small unmanned aerial vehicles. The investigation concerns the comparison between the acoustic signature of optimized and conventional propellers driven by brushless electric motors. This topic is particularly relevant due to the dramatic increase of the UAV market for civil and military purposes with multiple operational issues. The quietness and the efficiency of the propulsive system are key aspects in the design of advanced aerial vehicles and very often can lead to the success or failure of the mission. In addition to the experimental research, a numerical analysis based on the compact formulation of the Ffowcs-Williams/Hawking equation and a simple model for the broadband noise, is presented and discussed
Sound source mechanisms in under‐expanded impinging jets
No full textExperiments on the aeroacoustics of an under-expanded supersonic jet impinging on a flat plate are presented and thoroughly discussed. A wide range of nozzle pressure ratios and of nozzle-to-plate distances has been analyzed with particular attention to the behavior of the discrete component of the noise. The investigation has been carried out by means of acoustic, particle image velocimetry and wall pressure measurements. The analysis of the relationship between the acoustic data and the fluid dynamic fields allows to examine the different source mechanisms of the discrete component of the noise and to evaluate the link between the jet flow structure and the acoustic tone features. Specifically, two ranges of nozzle pressure ratio have been observed showing different acoustic behaviors, characterized by distinct mechanisms of discrete noise generation. These regions are separated by a range of nozzle pressure ratios where impinging tones are not observed. The present experimental data extend previously published results, improving the analysis of the connection between fluid dynamic and acoustic fields and leading to a better comprehension of the impinging tone source mechanisms
Flow configurations in a Y splitting-junction microchannel
Get PDFIn the present work, the flow field in a splitting-junction micro channel with a Y shape,
which is the simplest geometry to be employed for heat and mass transfer in micro-devices such
as micro-heat-exchangers and micro-mixers, is investigated experimentally using micro Particle
Image Velocimetry (microPIV). The angular divergence in the Y splitting is changed, as well as the
Reynolds number, in order to investigate the instantaneous and mean flow fields to determine
which configurations are more suitable for practical applications. The results show that the flow
configuration is strongly dependent on the Y shape angle, especially in the junction part, and that
there is also a significant dependence on the Reynolds number
Analysis of the characteristic acoustic tones of an impinging jet
No full textThe acoustic emission of a supersonic jet is an interesting and fundamental issue due to the several technological applications and the diverse physical aspects to be still clarified. An experimental analysis of the characteristic acoustic tones of a supersonic impinging jet has been carried out with a particular attention on the effect of the nozzle pressure ratio and the distance of the impinging surface. The screech tones, typical of an imperfectly expanded supersonic free jet, have been first investigated to have an idea of the deflection from the free jet behavior due to the impinging surface. Then the analysis has been focused on smaller distances of the impinging plate from the jet exit to evaluate the behavior of the impinging tones. The difference between screech and impinging tones, due to the different interactions in the generating
feedback mechanism, has been observed
Aeroacoustics and aerodynamics of impinging supersonic jets: Analysis of the screech tones
No full textThe interaction between acoustics and aerodynamics of a supersonic jet is an actual fundamental topic which has been a matter of discussion in the last decades. The present paper is devoted to the experimental analysis of free and impinging jets with particular attention on the effect of an impinging surface on screech tones. The acoustics is studied using free-field microphones, while Particle Image Velocimetry is used to investigate the velocity field. The analysis of acquired data allowed to verify and explain the coupling between acoustic discrete tones and mean and fluctuating flow velocities. (C) 2013 AIP Publishing LLC
Experiments and dns of a round jet with turbulent inlet
No full textExperimental and Direct Numerical Simulation data of a turbulent round jet fed by a turbulent pipe are compared in the near field. The Reynolds number achieved in both the experiment and the simulation, Re = 16000, allows a direct comparison of both the average and the fluctuating velocity statistics. In the experiments the jet is fed with olive oil droplets with a Stokes number St ' 1 whose dynamics is compared against the corresponding DNS simulation to asses the ability of particles to reproduce high order turbulence statistics and to asses the accumulation properties of inertial particles in the near field
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