1,721,199 research outputs found
Coherent structures identification from Wavelet analysis of PIV bidimensional velocity fields
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Wall pressure fluctuations in rectangular partial enclosures
No full textWall pressure fluctuations generated within rectangular partial enclosures (RPEs) have been studied experimentally for a broad range of geometrical parameters. The geometry represents a simplified version of a new generation trapped vortex combustor and consisted of a rectangular cavity connected to a neck of smaller size. Wall pressure fluctuations have been measured through wall mounted microphones providing single and multi-variate pressure statistics both in the physical space and in the Fourier domain. In order to interpret the pressure signals, aerodynamic and acoustic investigations have been carried out as well for several cavity-neck ratios. The analysis of the acoustic response of the cavity has been conducted both numerically and experimentally and a simple theoretical model has been proposed to predict the frequency of the acoustic resonances. The aerodynamic study has been carried out through PIV measurements that provided characterization in terms of the geometrical parameters of both the large-scale vortex generated within the cavity and the recirculation zone formed upstream of the neck. The use of the POD decomposition permitted us to correlate the dynamics of the recirculation with the observed pressure statistics. The aerodynamic and acoustic investigations allowed us to interpret exhaustively the wall pressure cross-statistics and to separate contributions induced by hydrodynamic and purely acoustic pressure fluctuations
"A new statistical model for anomalous scaling prediction in fully developed turbolence"
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Wavelet analysis of near-field pressure fluctuations generated by a subsonic jet
No full text"-"An experimental study of the pressure field generated by a subsonic, single stream,
round jet is presented. The investigation is conducted in the near-field region at
subsonic Mach numbers (up to 0.9) and Reynolds numbers Re > 105. The main
task of the present work is the analysis of the near-field acoustic pressure and
the characterization of its spectral properties. To this aim, a novel post-processing
technique based on the application of wavelet transforms is presented. The method
accomplishes the separation of nearly Gaussian background fluctuations, interpreted
as acoustic pressure, from intermittent pressure peaks induced by the hydrodynamic
components. With respect to more standard approaches based on Fourier filtering,
the new technique permits one to recover the whole frequency content of both the
acoustic and the hydrodynamic contributions and to reconstruct them as independent
signals in the time domain. The near-field acoustic pressure is characterized in
terms of spectral content, sound pressure level and directivity. The effects of
both the Mach number and the distance from the jet axis are analysed and the
results are compared with published far-field observations and theoretical predictions.
Simultaneous velocity/pressure measurements have been also performed using a hotwire
probe and a microphone pair in the near field. It is shown that the crosscorrelation
between the near-field acoustic pressure and the axial velocity is large (of
the order of 0.2) in the potential core region whereas large velocity/hydrodynamic
pressure correlations are located at the nozzle exit and downstream of the potential
core
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