Calcul numérique du bruit aérodynamique en régime subsonique

The evaluation of the noise produced by flows has reached a high level of importance in the past years. The physics surrounding flow-induced noise is quite complex and sensitive to various flow conditions like temperature, shape. Empirical models were built in the past for some special geometries but they cannot be used in a general case for a shape optimization for instance. Experimental aeroacoustic facilities represent the main tool for acoustic analyses of flow fields, but are quite expensive because extreme care must be exercised not to introduce acoustic perturbations in the flow (silent facilities). These tools allow a good analysis of the physical phenomena responsible for noise generation in the flow by a comparison of the noise sources and the flow characteristics (pressure, turbulence,). Nevertheless, the identification and location of noise sources to compare with flow structures requires quite complex methods.The numerical approach complements the experimental one in the sense that the flow characteristics are deeply analyzed where experiments suggest noise production. For the numerical approach, the turbulence modeling is quite important. In the past, some models were appreciated for their good prediction of some aerodynamic parameters as lift and drag for instance. The challenge is now to tune these models for a correct prediction of the noise sources. In the low subsonic range, the flow field is completely decoupled from acoustics, and noise sources can be computed from a purely hydrodynamic simulation before this information is transferred to an acoustical solver which will compute the acoustic field at the listener position. This post processing of the aerodynamic results is not obvious since it can introduce non-physical noise into the solution.This project considers the aspect of noise generation in turbulent jets and especially the noise generated by vortex pairing, as it occurs for instance in jet flows. The axisymmetric version of the flow solver SFELES has been part of this PhD research, and numerical results obtained on the jet are similar to the experimental values. Analyses performed on the numerical results are interesting to go to complete turbulence modeling for aeroacoustics since vortex pairing is one of the basic acoustical processes in vortex dynamics.Currently, a standard static Smagorinski model is used for turbulence modeling. However, this model has well known limitations, and its influence on the noise sources extracted from the flow field is not very clear. For this reason, it is planned to adopt a dynamic procedure in which the subgrid scale model automatically adapts to the flow. We planned also to perform simulations with the variational multiscale approach to better simulate the different interactions between large and unresolved scales. The commercial software ACTRAN distributed by Free Field Technologies is used for the computation of sound propagation inside the acoustic domain.Doctorat en Sciences de l'ingénieurinfo:eu-repo/semantics/nonPublishe

Numerical Simulations of Unsteady Flows around Reentry Capsules

info:eu-repo/semantics/publishe

Numerical acoustic modelling of a ventilation unit by 3D FEM and application to the design of an ANC feedforward system

Strong insulation in modern buildings and housing requires efficient ventilation systems. A popular solution is a decentralized system with one ventilation unit per room, but the noise emitted by such a unit then has a major impact on the comfort. In this research, it is intended to equip an existing ventilation unit with an active noise control (ANC) system to reduce its low-frequency noise emissions. The ANC system will be hosted in an additional duct deporting the air inlet aperture approximately one meter away from its original position. The one-channel feedforward ANC system has a reference microphone located between the fan and the anti-noise loudspeaker and an error microphone at the duct’s end. The transfer functions have been computed by a 3D FEM solver, between the fan and several reference and error microphone locations. Several combinations of reference/error microphone positions were then tested regarding the possible active attenuation of a white noise emitted by the primary source. Optimal control by the ANC controller was assumed, the optimal filter being computed with the help of the corresponding transfer functions. Theoretical attenuations were obtained and optimal positions were finally defined for the two microphones of the ANC system. The first results are finally discussed in this paper and raise some questions regarding the influence of the noise spectrum on the attenuations obtained.Silenthalpic (C7711

Numerical modelling and characterization of a heat exchanger

Strong insulation in modern building and housing requires efficient ventilation systems. A popular solution is a decentralized set-up with one ventilation unit per room. The noise emitted by a ventilation unit then has a major impact on the room comfort. In order to reduce the heat transfer to the outside, a ventilation unit is typically designed as a double flux-system with a heat exchanger. This exchanger has a noticeable impact on the acoustic behavior of the ventilation unit. It is therefore of interest to study its effect through numerical simulations. The numerical modelling of a realistic heat exchanger is presented in this paper. The exchanger is placed inside its ventilation casing and modelled using a double equivalent fluid homogenization. Unknown homogenization properties are retrieved in two steps. Acoustic transfer functions are first measured experimentally in order to characterize the propagation paths through the heat exchanger. In a second step, an optimization loop is computed with the numerical model of the heat exchanger. This allows to determine the homogenization properties fitting the measured transfer functions for each frequency. Finally the results for the characterized heat exchanger homogenization model are compared against measurement.Silenthalpic (C7711

Multi-objective design of single room ventilation units with heat and water recovery

The present paper describes the design improvement of a single-room ventilation unit. This ventilation system presents many advantages, how- ever, several drawbacks exist. The first one is the acoustic disturbance. As the facilities are directly installed within the rooms, the fans’ noise may create discomfort. Furthermore, in the cold or temperate climates, condensation or frost may appear. A dedicated management should then be implemented. Finally, as the system is not centralized, commu- nication between the different units is required to ensure the global sys- tem efficiency. A team of several industrial partners and research institutes tackles the above-mentioned issues in the frame of the “Silenthalpic” project. The project is split in three major tasks. To cor- rectly reduce the sound emission level (i), a spectral analysis of the noise emitted by an existing unit was undertaken, revealing that fre- quencies under 1kHz are mainly responsible for the noise disturbance. From this analysis, active and passive solutions for noise reduction are envisaged, showing encouraging trends. The next research aspect is the exchanger of the ventilation unit (ii). The constituting material is a new porous membrane allowing the humidity transfer (vapor or liquid). This specific exchanger is numerically modelled to predict its performances. The last considered problematic is the optimization of the ventilation and control strategies for the specific case of decentralized units (iii), taking advantage of sensors and recent communication technologies like IOT (Internet Of Things) to establish communication between decentralized units and ensure their consistent control. The association of the three aspects presented here should then lead to versatile and efficient ventilation systems

Multi-objective design of single room ventilation units with heat and water recovery

peer reviewedThe present paper describes the design improvement of a single-room ventilation unit. This ventilation system presents many advantages, however, several drawbacks exist. The first one is the acoustic disturbance. As the facilities are directly installed within the rooms, the fans’ noise may create discomfort. Furthermore, in the cold or temperate climates, condensation or frost may appear. A dedicated management should then be implemented. Finally, as the system is not centralized, communication between the different units is required to ensure the global system efficiency. A team of several industrial partners and research institutes tackles the above-mentioned issues in the frame of the “Silenthalpic” project. The project is split in three major tasks. To correctly reduce the sound emission level (i), a spectral analysis of the noise emitted by an existing unit was undertaken, revealing that frequencies under 1 kHz are mainly responsible for the noise disturbance. From this analysis, active and passive solutions for noise reduction are envisaged, showing encouraging trends. The next research aspect is the exchanger of the ventilation unit (ii). The constituting material is a new porous membrane allowing the humidity transfer (vapor or liquid). This specific exchanger is numerically modelled to predict its performances. The last considered problematic is the optimization of the ventilation and control strategies for the specific case of decentralized units (iii), taking advantage of sensors and recent communication technologies like IOT (Internet Of Things) to establish communication between decentralized units and ensure their consistent control. The association of the three aspects presented here should then lead to versatile and efficient ventilation systems.Silenthalpi

COASTVAR 2015-2018 : caractérisation de la variabilité littorale en Afrique de l'Ouest par une étude multi-échelle et multi-méthode [résumé]

International Conference AWA (ICAWA), Dakar, SEN, 09-/12/2014 - 11/12/201

COASTVAR 2015-2018 : caractérisation de la variabilité littorale en Afrique de l'Ouest par une étude multi-échelle et multi-méthode [résumé]

International Conference AWA (ICAWA), Dakar, SEN, 09-/12/2014 - 11/12/201