Papers by Romain Maréchal
Journal of Sound and Vibration, 2014
This paper deals with strategies for computing efficiently the propagation of sound waves in duct... more This paper deals with strategies for computing efficiently the propagation of sound waves in ducts containing passive components. In many cases of practical interest, these components are acoustic cavities which are connected to the duct. Though standard Finite Element software could be used for the numerical prediction of sound transmission through such a system, the method is known to be extremely demanding, both in terms of data preparation and computation, especially in the mid-frequency range. To alleviate this, a numerical technique that exploits the benefit of the FEM and the BEM approach has been devised. First, a set of eigenmodes is computed in the cavity to produce a numerical impedance matrix connecting the pressure and the acoustic velocity on the duct wall interface. Then an integral representation for the acoustic pressure in the main duct is used. By choosing an appropriate Green's function for the duct, the integration procedure is limited to the duct-cavity interface only. This allows an accurate computation of the scattering matrix of such an acoustic system with a numerical complexity that grows very mildly with the frequency. Typical applications involving Helmholtz and Herschel-Quincke resonators are presented.
Boundary Elements and Other Mesh Reduction Methods XXXII, 2010
This paper deals with strategies for computing efficiently the propagation of sound waves in duct... more This paper deals with strategies for computing efficiently the propagation of sound waves in ducts with acoustic lining at its walls. Though efficient these treatments seem to have reach their limit and there is still a need for considering other passive techniques to reduce further the sound radiation at the duct exit. In most cases of practical interest, these added acoustics components can be modelled as acoustic cavities which are connected to the duct and can be either purely reactive or dissipative. The assessment of the efficiency of such a system requires a precise knowledge of the acoustic field in the duct. Though standard Finite Element (FE) software could, in principle, be used for this purpose, a full FE model would be extremely demanding especially in the mid-frequency range and this can have a negative impact when, for instance, some efficient optimizations are needed. In the present work,we present a new numerical procedure that judiciously exploit the benefit of the FEM and the BEM approach. First, a set of FE eigenmode are computed in the cavity to produce a numerical impedance matrix connecting the pressure and the acoustic velocity on the duct wall interface. Then an integral representation for the acoustic pressure in the main duct is used. The presence of acoustic liners on the walls of the duct is taken into account via an appropriate modal decomposition of the Green's function. Typical applications involving Helmholtz resonators and Herschel-Quincke tubes are presented. We show that our algorithm allows a very fast and accurate computation of the scattering matrix of such a system with a numerical complexity that grows very mildly with the frequency.
Aeroacoustics Analogies (AA) initiated by Lighthill in the 50's are able to give the acoustic fie... more Aeroacoustics Analogies (AA) initiated by Lighthill in the 50's are able to give the acoustic field radiated by an aero-dynamic flow. In this work, the computation of the Lighthill-Curle's integral formulation for the prediction of the upstream pressure field in a two dimensional duct is presented. We are considering in particular the emitted noise due to low-Mach number flows through geometrical singularities placed in the duct (circular obstacle and diaphragm). The Lighthill stress tensor corresponding to turbulent velocity fluctuations is obtained via a commercial software (ANSYS FLUENT). It is shown that sound levels generated upstream can be particulary sensitive to the wall pressure fluctuations on the obstacle. Mots clefs : 3 maximum : Analogie de Lighthill-Curle, Acoustique en conduit, Bruit de diaphragme
Over the last decade, the concept of Herschel-Quincke (HQ) waveguide resonators has been the subj... more Over the last decade, the concept of Herschel-Quincke (HQ) waveguide resonators has been the subject of intensive research for fan noise control in aircraft turbofan engines. The approach has been numerically and experimentally tested in combination with typical acoustic liners for both inlet and aft fan noise reduction (see for instance [1, 2] and references therein). In particular, results have demonstrated potential of the HQ tubes for the Blade Passing Frequency (BPF) tone attenuation whereas the liner is effective to reduce broadband noise. More recently, adaptive HQ tubes have been developed in order to target the BPF tone for different operating conditions . Despite the progress being made, it is thought that additional research effort should be carried out to evaluate and optimize such an acoustic system. To this end, a new hybrid numerical technique for the computation of the scattering matrix has been devised by the present authors . The technique which is inspired from the numerical model developed in [2] offers two major improvements: (i) the lined portion of the duct is of finite extent and (ii) the exact shape of the HQ tube is taken into account. The HQ-liner system consists of a regular array of HQ tubes installed around the circumference A +
The Herschel-Quincke (HQ) tubes, consisting in putting tubes in derivation along a main acoustic ... more The Herschel-Quincke (HQ) tubes, consisting in putting tubes in derivation along a main acoustic wave guide, are used as passive devices to control fan noise. In order to assess the efficiency of this system, a new mixed analytical-numerical model is presented. The technique relies on combining Finite Element techniques to accurately describe the HQ tube with an integral representation for the acoustic pressure in the main duct. The presence of acoustic liners on the walls of the duct is taken into account via an appropriate modal decomposition of the Green's function. We show that our algorithm allows a very fast and accurate computation of the scattering matrix of such a system with a numerical complexity that grows very mildly with the frequency. Results show that 'nearly' optimal configurations can be quickly identified with a very small computational expense.
Acta Acustica united with Acustica, 2011
This paper deals with strategies for computing efficiently the propagation of sound wavesinlined ... more This paper deals with strategies for computing efficiently the propagation of sound wavesinlined ducts containing passive components. In most cases of practical interest, these added acoustics components can be modelled as acoustic cavities which are connected to the duct and can be either purely reactive or dissipative.The assessment of the efficiencyo fs uch as ystem requires ap recise knowledge of the acoustic field in the duct. In the present work anew numerical procedure that judiciously exploit the benefitofthe FEM and the mode matching approach is presented. First, aset of FE eigenmode are computed in the cavity to produce anumerical impedance matrix connecting the pressure and the acoustic velocity on the duct wall interface. Then an integral representation for the acoustic pressure in the main duct is used. The presence of acoustic liners on the walls of the duct is taken into account via an appropriate modal decomposition of the Green'sf unction. Typical applications involving Helmholtz resonators and side branch ducts (Herschel-Quincketubes)are presented. We showthat our algorithm allows avery fast and accurate computation of the scattering matrix of such asystem with anumerical complexity that grows very mildly with the frequency. PACS no. 43.20.Mv,43.50.Gf,43.55.Ka 966 ©S.Hirzel Verlag · EAA Maréchal et al.:S cattering matrix of lined ducts ACTA ACUSTICA UNITED WITH ACUSTICA Vol. 97 (2011)
3rd EUropean Conference …, 2009
The Herschel-Quincke (HQ) tubes, consisting in putting tubes in derivation along a main wave guid... more The Herschel-Quincke (HQ) tubes, consisting in putting tubes in derivation along a main wave guide, are used as passive devices to control fan noise. In order to assess the efficiency of this system, analytical and semi-analytical models proposed in the literature all rely on the assumption that only plane waves are allowed to propagate in the tube which then restrict the pressure and the normal acoustic velocity to be constant over the duct-tube interface. We show that these simplifications are too limited especially when dealing with high frequency modes in the main duct. To make some progress, a new mixed analytical-numerical approach is proposed. The method, based on the discrete modal analysis of the tube allows to take into account its exact shape as well as the non-uniformity of the acoustic velocity at the interface.
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Papers by Romain Maréchal