1,721,040 research outputs found
Acceleration and wall pressure fluctuations generated by an incompressible jet in installed configuration
No full textIn this work, the cross-statistics of acceleration and wall pressure fluctuations generated by an incompressible jet interacting with a tangential flat-plate are presented. The results are derived from an experimental test campaign on a laboratory-scale model involving simultaneous velocity and wall pressure measurements. The pressure footprint of the jet on the surface was measured through a cavity-mounted microphone array, whereas pointwise velocity measurements were carried out by a hot wire anemometer. The time derivative of the velocity signal has been taken as an estimation of the local acceleration of the jet. The multivariate statistics between acceleration and wall pressure are achieved through cross-correlations and cross-spectra, highlighting that the causality relation is more significant in the potential core where the Kelvin–Helmholtz instability is dominant. The application of a conditional sampling procedure based on wavelet transform allowed us to educe the acceleration flow structures related to the energetic wall-pressure events. The analysis revealed that, unlike the velocity, the acceleration signatures were detected only for positions where the jet had not yet impinged on the plate, their shape being related to a convected wavepacket structure
Numerical experiments on strongly turbulent thermal convection in a slender cylindrical cell
No full textAeroacoustics research in Europe: The CEAS-ASC report on 2019 highlights
No full textThe Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on a European scale and European aeronautics activities internationally. In this context, “aeroacoustics” encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. This paper is a report on highlights of aeroacoustics research in Europe in 2019, compiled from information provided to the ASC of the CEAS. In addition, during 2019, a number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are also summarised in this article, as well as highlights from other programmes funded by national programmes or by industry. Furthermore, a concise summary of the CEAS-ASC annual scientific workshop: “New Materials for Applications in Aeroacoustics” held in the University of Roma Tre, Italy in September 2019 is included in this report. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection
An experimental investigation of the wall pressure field induced by a low and moderate mach numbers jet on a tangential flat plate
No full textIn this work an experimental analysis of the wall pressure field generated by the interaction between a subsonic jet and a flat plate parallel to the nozzle axis is performed. The analysis is the continuation of previous studies carried out by the same authors on the interaction between a jet and a flat plate in an incompressible jet facility. In the present work a similar installed configuration has been analyzed exploiting a compressible jet facility in order to address the effect of the transition from incompressible to low/moderate compressible flow conditions. The pressure footprint on the flat plate was measured in both the streamwise and spanwise directions through a flush-mounted microphone array for different radial distances of the surface from the jet. Wall pressure fluctuations have been characterized in terms of statistical and spectral quantities. Implications for modelling of the wall pressure fluctuations are considered by the application of the Corcos’ model to the coherence functions in both the streamwise and spanwise directions. Specifically, the Corcos’ model was verified for all the jet flow velocities, the increase of the jet Mach number having the effect to enhance the jet flow development over the plate and to speed up the approach of a quasi-equilibrium turbulent boundary layer
Jet noise sources for chevron nozzles in under-expanded condition
No full textImperfectly expanded jet flows are known to have additional noise sources known as Screech and broadband shock-associated noise. They are generated by the interaction between the instability waves that propagate from the lip of the nozzle and the shock cell structures. In this study, thorough experimental investigations were carried out on chevron nozzles to assess the importance of chevron parameters such as the chevron count and chevron penetration angle on the pressure field emitted by the jet. Data were acquired in the state-of-the-art aeroacoustic facility at the University of Bristol. Acoustic measurements such as pressure spectra, directivity and overall sound pressure levels along with near-field measurements were acquired for jet Mach numbers ranging from M = 1.1–1.4. Fourier-based and Wavelet-based analyses were used to highlight the different features of the various tested nozzles. Wavelet decomposition results highlight that the presence of the chevrons reduce the acoustic noise especially at a higher axial distance with increased levels of noise reduction achieved by chevron nozzle with deep penetration angle
Experimental study on statistical properties of coherent structures and intermittency in a channel flow
No full text
Structure function exponents and probability density function of the velocity difference in turbulence
No full textPrandtl number effects in convective turbulence
No full textThe effect of Prandtl number on the dynamics of a convective turbulent
flow is
studied by numerical experiments. In particular, three series of experiments
have been
performed; in two of them the Rayleigh number spanned about two decades
while the
Prandtl number was set equal to 0.022 (mercury) and 0.7 (air). In the third
series, in
contrast, we fixed the Rayleigh number at 6×105 and the
Prandtl number was varied
from 0.0022 up to 15. The results have shown that, depending on the Prandtl
number,
there are two distinct flow regimes; in the first (Pr[lsim ]0.35)
the flow is dominated by
the large-scale recirculation cell that is the most important ‘engine’
for heat transfer.
In the second regime, on the other hand, the large-scale flow plays a negligible
role
in the heat transfer which is mainly transported by the thermal plumes.For the low-Pr regime a model for the heat transfer is derived
and the predictions
are in qualitative and quantitative agreement with the results of the numerical
simulations and of the experiments. All the hypotheses and the consequences
of the model
are directly checked and all the findings are consistent with the predictions
and with
experimental observations performed under similar conditions. Finally,
in order to
stress the effects of the large-scale flow some counter examples are shown
in which
the large-scale motion is artificially suppressed.</jats:p
On the Application of Wavelet Transform in Jet Aeroacoustics
No full textWavelet transform has become a common tool for processing non-stationary signals in many different fields. The present paper reports a review of some applications of wavelet in aeroacoustics with a special emphasis on the analysis of experimental data taken in compressible jets. The focus is on three classes of wavelet-based signal processing procedures: (i) conditional statistics; (ii) acoustic and hydrodynamic pressure separation; (iii) stochastic modeling. The three approaches are applied to an experimental database consisting of pressure time series measured in the near field of a turbulent jet. Future developments and possible generalization to other applications, e.g., airframe or propeller noise, are also discussed
- …
