The screech tones generated by a three-dimensional planar underexpanded jet are computed directly using compressible large eddy simulation (LES). The jet operates at fully expanded Mach number M j = 1.55, with Reynolds number Re h = 6 × 10 4 . The LES strategy is based on explicit selective filtering with spectral-like resolution, and low dispersion and low dissipation numerical algorithms are implemented to allow direct noise computation of the phenomenon. The investigation of the numerical results shows that the flow development, the shock cell structure and the upstream acoustic field are well reproduced by the computation. Flow visualization of shock/vortex interactions within the third shock-cell provides evidences that screech sound sources can be interpreted using the shock-leakage theory.
For modern cars, aerodynamic noise is becoming the major source of annoyance during peri-urban trips. To take this point into consideration from the vehicle development and to improve the interior comfort, appropriate numerical methods have to be developed. The estimation of the broadband noise generated by low Mach number flows about M∼0.1, considered in this study, are obtained by applying a two-step method combining incompressible CFD calculations with acoustic analogy. In this paper, the advanced-time algorithm is developed to allow the estimation of all the terms of Ffowcs Williams and Hawkings' equation and particularly the volume terms. The noise corresponding to a cylinder flow is then used to validate this approach and to compute the broadband noise radiated by a 3-D incompressible and turbulent flow. The algorithm is then applied to a wall-mounted half-cylinder corresponding to a simplified side-mirror shape. In order to validate the half-cylinder aeroacoustic calculations, the numerical results are favourably compared to measurements recently carried out.
Parabolic equation models in 3D usually apply the "staircase" approximation to general rangevarying interfaces between adjacent layers. This is the simplest technique available: it consists in neglecting range and azimuthal derivatives in the associated interface conditions. Our aim in this paper is to analyze the influence of the stair-step approximation technique, common to most 3D PE models, on a one-way sound wave propagation problem. We present a new finite-element 3D narrowangle PE model which accurately treats the variable interface conditions. This is accomplished by using (i) an appropriate parabolized condition of the same aperture as the parabolic equation used, and (ii) a new change-of-variable technique which does not require any homotheticity condition of the layers as in previous works. Numerical simulations for the 3D wedge problem are presented. The convergence of the numerical solutions with respect to the azimuth is investigated. Unlike other 3D PE models working in cylindrical coordinates, the convergence tests have been carried out using a range-dependent number of points in azimuth. Numerical solutions obtained with the newly developed model are compared with a reference solution based on the image source and with a solution obtained with a 3D PE model that uses a stair-step technique.
La digue du Braek est un ouvrage de défense contre la mer du port de Dunkerque. Cette digue en enrobé bitumineux de 6 km de long borde une plage macrotidale orientée OSO-ENE. Le transport éolien a été évalué le long d'un profil transversal allant du haut de plage au sommet de la digue à l'aide de pièges à sédiment, pour des conditions de vent obliques. Les vitesses de vent associées ont été déterminées grâce à des anémomètres à coupelles placés à différentes hauteurs sur des mâts. Les résultats montrent une accélération du vent sur le versant de la digue exposé, similaire à l'effet de rampe observé sur les versants dunaires, ainsi que des quantités de sable piégé supérieures sur l'asphalte que sur le sable. Mots-clés : Transport éolien-Mesures in situ-Digue en enrobé
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