Free Field Technologies

Mont-Saint-Guibert, Belgium

Free Field Technologies

Mont-Saint-Guibert, Belgium
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Van Den Nieuwenhof B.,Free Field Technologies | Lielens G.,Free Field Technologies | Rosseel E.,Free Field Technologies | Dangla V.,Free Field Technologies | And 3 more authors.
23rd AIAA/CEAS Aeroacoustics Conference, 2017 | Year: 2017

The noise radiated from the intake of turbofan engines corresponds to a significant noise source at aircraft level, which is generally controlled by acoustic treatments (liners) applied on the engine and the nacelle. The positioning of these liners as well as their geometric properties are variables in the acoustic design of the nacelle. These parameters have to be optimized to achieve the required aircraft acoustic performance while taking into account the integration, industrial and cost constraints. This paper proposes a framework for an efficient solution for this optimization problem. A finite element scheme is used to solve the convected Helmholtz equation that accurately describes the wave propagation in the nacelle duct as well as in the far-field. Locally-reacting admittance boundary conditions are used to model the acoustic liners. The optimization problem is stated with the objective to identify the positioning and impedance values of the acoustic liner in such a way that the far-field pressure level is minimal at a target frequency. A model reduction strategy based on a condensation of the duct and exterior acoustic problem on the surface of the acoustic treatments is presented as a mean to drastically speed-up the optimization process. A numerical application is demonstrated on a typical 2D axisymmetric nacelle configuration. Comparisons between the optimal designs as well as the computational performance of the proposed approach are assessed. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.


Gustafsson M.,Volvo | Jacqmot J.,Free Field Technologies | Caro S.,Free Field Technologies
Proceedings of ISMA 2010 - International Conference on Noise and Vibration Engineering, including USD 2010 | Year: 2010

In this paper, a technique to compute the noise radiated by a large truck engine is presented. This technique is of particular interest at Volvo Powertrain, where the design process should be robust, fast, reliable, and involve the least possible human interventions. It will be shown that the technique proposed here fulfills most needs. The computational process is the following. In a first step, the vibration is computed using the commercial tools FEV™ Virtual Engine and ANSYS®. In a second step, the result files are used in an acoustic radiation computation using the commercial tool ACTRAN™. In the paper the focus is put on the methodology, its performance for large radiation problems, and the possibilities to automate the process. An experimental validation is presented on a real truck engine in a semi-anechoic room. Over the whole range of regimes studied (waterfall up to 2kHz) the correlations are excellent. The free field overall sound power level from 600 to 1900 rpm full load is predicted within 2 dB compared to measurement. The 3rd octave band average is also predicted within 2 dB from 10 Hz up to 2kHz. The method is proven to be very accurate with respect to noise prediction; using it opens the door to virtual prototyping and components are easily replaceable during the development phase. The human intervention during the simulation process is reduced to its minimum and the computational times are compatible with industrial constraints.


D'Udekem D.,Free Field Technologies | Saitoh M.,Free Field Technologies | Van Den Nieuwenhof B.,Free Field Technologies | Yamamoto T.,Nissan Motor Co.
SAE Technical Papers | Year: 2011

During the acceleration of a vehicle, the contribution of the exhaust noise to the interior sound pressure level is significant. The acoustic insulation brought by the trim components must be designed with that consideration in mind. As such, there is an increasing need for developing reliable methods for predicting the airborne noise transmission between the exhaust system and the sound pressure level at the passenger's ears, taking into account the positive impact of various trim components. This paper presents a methodology that has been developed for addressing this need. Based on a finite/infinite element method, the computational procedure is divided in two steps: 1The first step involves the exterior acoustic field all around the vehicle. The acoustic pressure field on the exterior surface of the vehicle is computed by considering the exhaust system as acoustic source;2The second step consists in computing the interior vibro-acoustic response of the vehicle by using the surface pressure from step one as excitation applied to the trimmed body finite element model. This second step relies on a FE modal-based approach for the efficient modeling of large trimmed structures coupled to acoustic cavities. In this approach, the trim components are represented by their impedance matrices reduced to the interface degrees of freedom with the body structure and the interior acoustic cavity. These reduced impedance matrices are then projected on the structure/fluid modal bases and injected in the coupled modal system; as such the trim components are accurately taken into account when the vibro-acoustic modal model of the vehicle is solved. The paper gives the details of the two steps of this approach as well as the key ingredients related to this original technique. Some real life validation cases (including some comparisons with measurements) are presented, proving the reliability of the method and its efficiency in an industrial automotive context. Copyright © 2011 SAE International.


Detandt Y.,Free Field Technologies
Journal of Sound and Vibration | Year: 2015

The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. Each year the committee highlights some of the research and development projects in Europe. This paper is the 2014 issue of this collection of Aeroacoustic Highlights, compiled from informations submitted to the CEAS-ASC. The contributions are classified in different topics; the first categories being related to specific aeroacoustic challenges (airframe noise, fan and jet noise, helicopter noise, aircraft interior noise) and two last sections are respectively devoted to recent improvements and emerging techniques and to general advances in aeroacoustics. For each section, the present paper focus on accomplished projects, providing the state of the art in each research category in 2014. A number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are summarised in this paper, as well as highlights funded by national programmes or by industry. © 2015 Elsevier Ltd. All rights reserved.


Robin X.,Free Field Technologies | Driot N.,BorgWarner Turbo Systems Engineering GmbH | Jacqmot J.,Free Field Technologies
42nd International Congress and Exposition on Noise Control Engineering 2013, INTER-NOISE 2013: Noise Control for Quality of Life | Year: 2013

Noise generation in turbochargers becomes an important source of inconvenience in modern vehicle. Noise sources are now well known but they are complex because of their multiplicity and the physics involved. This noise is mostly studied experimentally but this paper presents an innovative simulation strategy to study one of the major components of the turbocharger noise: the structure borne noise. First of all, the methodology based on a multi-disciplinary approach is presented. The dynamic behavior is assessed using a modal analysis technique. The turbocharger is excited through the supports of the rotor bearings. In a second step, an acoustic finite element model considers the vibration of the structure as a boundary condition to radiate acoustic energy in the surrounding air. The paper focuses on the results of the acoustic radiation all around the turbocharger. A first analysis shows that the acoustic radiation is led by the modes of the structure. Nevertheless, not only the level of vibration is important but also the shape of the modes must be taken into account. This is an important conclusion in the frame of the understanding of the acoustic behavior. The effect of the excitation itself on the acoustic radiation is also considered. Copyright© (2013) by Austrian Noise Abatement Association (OAL).


Copiello D.,Free Field Technologies | Lielens G.,Free Field Technologies | Sambuc C.,Free Field Technologies
Sound and Vibration | Year: 2015

Total vehicle noise is significantly impacted by the contribution of intake and exhaust lines. This article uses a finite element method (FEM), integrating advanced visco-thermal dissipative models, to analyze specific intake and exhaust line components. In particular, the acoustic performance of a catalytic converter and an air filter are simulated. Their models include the dissipative effects of small ducts and anisotropic porous materials respectively.


Pietrzyk A.,Volvo Car Corporation | Beskow D.,Volvo Car Corporation | Moroianu D.,Volvo Car Corporation | Cabrol M.,Free Field Technologies | Detandt Y.,Free Field Technologies
22nd International Congress on Sound and Vibration, ICSV 2015 | Year: 2015

The design of modern car exterior is mainly influenced by aerodynamic performances. The side mirror shape is optimized to influence positively its contribution to the drag forces. An additional constraint plays a role on side mirror designs: above lOOkm/h, the noise generated by the side-mirror wake plays a significant role on the interior noise. The present paper focuses on the validation of simulation techniques to predict the exterior noise due to the aeroacoustic sources, located in the wake of the side mirror and in the large turbulent region close to the side window and the A-pillar. This qualification of the exterior noise simulations is aligned with the objectives of car manufacturers to reduce the exterior pass-by noise level, but is also a prerequisite for interior noise simulations where the pressure on the car body surface and windows will be considered as input for the vibro-acoustic simulation.


Van Herpe F.,PSA Peugeot Citroën | D'Udekem D.,Free Field Technologies | Jacqmot J.,Free Field Technologies | Kouzaiha R.,Free Field Technologies
SAE Technical Papers | Year: 2012

Nowadays, the interior vehicle noise due to the exterior aerodynamic field is an emerging topic in the acoustic design of a car. In particular, the turbulent aerodynamic pressure generated by the air flow encountering the windshield and the side windows represents an important interior noise source. As a consequence PSA Peugeot Citroën is interested in the numerical prediction of this aerodynamic noise generated by the car windows with the final objective of improving the products design and reducing this noise. In the past, several joint studies have been led by PSA and Free Field Technologies on this topic. In those studies (Ref.2 and 3), an efficient methodology to predict the noise transmission through the side window has been set-up (Figure 1). It relies on a two steps approach: the first step involves the computation of the exterior turbulent field using an unsteady CFD solver (in this case EXA PowerFlow). The second step consists in the computation of the vibro-acoustic transmission through the side window using the finite element vibro-acoustic solver Actran. Figure 1Simulation Process The present paper extends this methodology for the handling of multiple windows, i.e. the two front side windows and the windshield. The complete car cavity is modeled as well. First, a complete description of the method and the finite element model is provided, from the boundary conditions to the different components involved, like the windows, the seals and the car cavity. The total wind noise level results and the relative contributions of the different windows are then presented and compared to measurements for a real car model. The influence of the flow yaw angle (0° vs. 10° orientation) is also assessed. Copyright © 2012 SAE International.


Legendre C.,Free Field Technologies | Lielens G.,Free Field Technologies | Coyette J.-P.,Free Field Technologies
Proceedings - European Conference on Noise Control | Year: 2012

Noise propagation mechanisms in presence of a rotational flow are currently receiving some attention from the aircraft industry. Different methods are used in order to compute the acoustic wave propagation in sheared flows in terms of pressure perturbations (e.g. LEE, Lilley's and Galbrun's equations). Nevertheless, they have drawbacks in terms of computational performance (high number of DOFs per node, inadequacies of classical numerical schemes like standard FE). In contrast with other studies, in this work, the fluctuating total enthalpy is selected as the main variable in order to describe the acoustic field, which obeys to a convected wave equation with coefficients depending on flow variables obtained by linearization of momentum (Crocco's form), energy and continuity equations. The resulting 3D convected wave operator is an extension of Mohring acoustic analogy, able to predict the sound propagation through rotational flows in the subsonic regime and is well adapted to FE discretization. A 2D convected wave equation is generated from the previous operator. This is followed by a numerical solution based on FEM, able to handle two types of boundary condition, non reflecting BC and incident plane wave excitation. The numerical results are used to estimate the reflection coefficient generated by the shear flow. The new acoustic wave operator is compared to well-known theories of flow acoustics (Pridmore-Brown wave operator) and shows promising results. Finally additional development steps are presented in order to further improve the new operator. © European Acoustics Association.


Jacqmot J.,Free Field Technologies | Guerville F.,Alstom | Burd D.R.,Free Field Technologies
International Conference on Noise and Vibration Engineering 2012, ISMA 2012, including USD 2012: International Conference on Uncertainty in Structure Dynamics | Year: 2012

This paper provides a method for assessing the acoustic performance of complex HVAC duct systems. It includes a theoretical description of acoustic duct modes and the way to handle them in a finite element context to produce a purely non-reflecting boundary condition. The method is applied to an HVAC system used in a railway equipment. The transmission loss i.e. the ratio of incident to transmitted acoustic power (TL) is computed as well as the acoustic field in each sub-component. The geometric dimensions of the inlet and outlet sections directly drive the TL, primarily by controlling the frequency at which higher order duct modes appear. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved.

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