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Bogey C.,Ecole Centrale Lyon | Marsden O.,CNRS Fluid Mechanics and Acoustics Laboratory
AIAA Journal | Year: 2016

Two isothermal round jets at a Mach number of 0.9 and a diameter-based Reynolds number of 2 × 105 have been computed by compressible large-eddy simulation using high-order finite differences on a grid of 3.1 billion points. At the exit of a straight pipe nozzle in which a trip forcing is applied, the jet flow velocity parameters, including the momentum thickness and the shape factor of the boundary layer, the momentum-thickness-based Reynolds number, and the peak turbulence intensity, roughly match those found in experiments using two nozzles referred to as the ASME and the conical nozzles. The boundary layer is in a highly disturbed laminar state in the first case and in a turbulent state in the second. The exit flow conditions, the shear-layer and jet flowfields, and the far-field noise provided by the large-eddy simulation are described. The jet with the ASME-like initial conditions develops a little more rapidly, with slightly higher turbulence levels than the other. Overall, however, the results obtained for the two jets are very similar, and they are in good agreement with measurements available forMach0.9 jets. In particular, this similarity holds for the far-field spectra. Because the ASMEnozzle has been reported to yield higher noise levels than the conical nozzle, this suggests that the nozzle-exit conditions in the large-eddy simulation do not adequately reflect those in the experiments and/or that the link between the noise differences and the jet initial conditions using the two nozzles is not as simple as was first thought, and that other parameters, associated for instance with the nozzle geometry such as the presence of pressure gradients, may also play an important role. © 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Koussa F.,French Scientific and Technical Center for Building | Defrance J.,French Scientific and Technical Center for Building | Jean P.,French Scientific and Technical Center for Building | Blanc-Benon P.,CNRS Fluid Mechanics and Acoustics Laboratory
Applied Acoustics | Year: 2013

This research work aims at evaluating the acoustic performance of conventional and low height gabions noise barriers. On one hand, in situ as well as scale model measurements at a scale of 1:10 have been carried out to assess the intrinsic acoustic properties of a 3 m high gabions barrier. Single number ratings of transmission and reflection indices reached 20 dB and 5 dB, respectively. On the other hand, numerical simulations using a 2D boundary element method (BEM) and scale model measurements are carried out to study the effectiveness of low height gabions noise barriers when they are inserted in dense urban areas. The agreement between numerical and scale model measurements results is satisfactory. The effectiveness of low height gabions noise barriers is significant for receivers of limited height and the insertion loss values can reach 8 dB(A) behind the barrier. This confirms that gabions noise barriers are possible candidates as useful devices for environmental noise reduction. © 2012 Elsevier Ltd. All rights reserved.

Rozenberg Y.,ONERA | Roger M.,Ecole Centrale Lyon | Roger M.,CNRS Fluid Mechanics and Acoustics Laboratory | Moreau S.,Universite de Sherbrooke
AIAA Journal | Year: 2010

This paper deals with the experimental validation of an analytical trailing-edge noise model dedicated to low-speed fans operating in free field. The model is intrinsically related to the aerodynamics of the blades and should lead to a useful fast-running tool to be included in a blade-design process in an industrial context. The investigations are made on a two-bladed low-speed axial fan without shroud, installed inside an anechoic room. The blades are instrumented with two sets of embedded small-size microphones (2.5 mm diam), and the wall-pressure signals are acquired via a slip ring mounted on the fan axis. The chord-based Reynolds number is about 200,000, and the tip Mach number about 0.07. The data base is completed by far-field measurements made with a single microphone on a moving support. The analytical model is based on a previously published extension of Amiet's trailing-edge noise theory. A blade is split into several strips in the spanwise direction, and the model is applied to each strip. For this the input data are interpolated from the measurements performed with the aforementioned sets of microphones. The trailing-edge noise model is more reliable for observer positions within ±30° from the fan-rotation plane. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.

Sebastien C.,Geoservices | Michel L.,CNRS Fluid Mechanics and Acoustics Laboratory
International Journal of Multiphase Flow | Year: 2011

New technology combined to the rise of the barrel price make wet gas flow metering of primary importance. A Venturi and a multienergy gamma ray hold-up meter provide capital information to estimate gas and liquid flow rates with the required metering accuracy. Starting from Navier-Stokes' equations, the two-phase flow is modeled with a three 1D equations system for gas, liquid droplets and liquid film. Hypotheses are added to reduce the dynamical system to a simplified and operational two scalar equation model. Based on this physical description of the film-core flow, this new model is tested over experimental data. Finally, three remaining coefficients are calibrated and modeled thanks to empirical correlation with non-dimensional numbers. © 2010 Elsevier Ltd.

Bos W.J.T.,CNRS Fluid Mechanics and Acoustics Laboratory | Kadoch B.,Aix - Marseille University | Schneider K.,Aix - Marseille University
Physical Review Letters | Year: 2015

The angle between subsequent particle displacement increments is evaluated as a function of the time lag in isotropic turbulence. It is shown that the evolution of this angle contains two well-defined power laws, reflecting the multiscale dynamics of high-Reynolds number turbulence. The probability density function of the directional change is shown to be self-similar and well approximated by an analytically derived model assuming Gaussianity and independence of the velocity and the Lagrangian acceleration. © 2015 American Physical Society.

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