Christophe Schram

von Karman Institute for Fluid Dynamics

This paper elucidates the link between the near-wake development of a circular cylinder coated with a porous material and the measured aerodynamic-sound attenuation by formulating the related flow-induced noise as a diffraction problem. For this purpose, acoustic-beamforming and flow-visualisation techniques are combined with analytical modelling....

Unsteady wall pressures impact, to a large degree, the aerodynamic and aeroacoustic performance of aerodynamic bodies submersed in a flow. The empirical calibration of remote microphone probes (RMP), which tend to be deployed to acquire unsteady wall pressures, can introduce spurious resonance into the sensor transfer function (TF) due to the diffe...

The aerodynamics and aeroacoustics of a scaled model H-Darrieus vertical axis wind turbine (VAWT) with end plates and supporting structures is investigated at its design operational regime. A high-fidelity hybrid Lattice Boltzmann Method/Very Large Eddy Simulation model is achieved and coupled to an in-house aeroa-coustic propagation code SherFWH b...

The aerodynamic performance of a complete scale model of a H-Darrieus vertical axis wind turbine (VAWT) with actual end plates and mast is investigated at different tip-speed ratios with a high-fidelity hybrid Lattice Boltzmann /Very Large Eddy Simulation (LB-VLES) Method. The power curve from the simulation predicts the general trend and peak valu...

Integrating a porous material into the structure of an aerofoil constitutes a promising passive strategy for mitigating the noise from turbulence-body interactions that has been extensively explored in the past few decades. When a compact permeable body is considered in the aeroacoustic analogy derived by Curle to predict this noise source, a dipol...

The noise associated with the growing presence of unmanned aerial vehicles such as professional drones is becoming a concern. The buzzing noise emitted by multicopter drones is particularly distracting and annoying. The root mechanisms causing this tonal noise in multicopter configurations are however poorly understood and constitute the focus of t...

A small didactic wind tunnel demonstrator has been designed and manufactured at the von Karman Institute for Fluid Dynamics to illustrate the physical principles at stake in flow-induced noise generation, offer an audible perception of the effectiveness of noise-mitigation strategies, and serve as a practical test bench for aeroacoustic education a...

Noise measured in the test section by the serrated airfoil interacting with the turbulence shed by an upstream cylindrical rod at a free-stream flow speed of 20 m/s. The audio files are band-filtered in the range 600-800 Hz.

Noise measured in the test section by the baseline airfoil interacting with the turbulence shed by an upstream cylindrical rod at a free-stream flow speed of 20 m/s. The audio files are band-filtered in the range 600-800 Hz.

A numerical approach to predict broadband trailing-edge noise for low Mach number flows is presented. It is based on the combination of a Helmholtz solver to propagate sound waves with a sound source term computed stochastically. The sound propagation is performed in the frequency domain using a high-order finite element solver. The stochastic appr...

The flow field on solid and porous airfoils subjected to turbulence shed by an upstream cylindrical rod and the corresponding far-field noise radiations are studied through particle image velocimetry (PIV) and microphone measurements, respectively. Three different Reynolds numbers based on the rod diameter are considered in a range between 2.7×104\...

Aerodynamic noise emitted by low-speed axial fans has been receiving increasing attention in various sectors of high societal impact, such as automotive and HVAC systems. In this framework, turbulence interaction, flow non-uniformities, trailing-edge boundary layer fluctuations and blade-tip leakages are different mechanisms generating aeroacoustic...

The low-speed fans that are used for automotive engine cooling contribute to a significant part of the global noise emitted by the vehicle. Automotive engine cooling manufacturers are therefore interested in developing low-order noise prediction methodologies that include the radiated sound in pre-design optimization cycles. Two among the most infl...

This paper presents a new data-driven approach for the establishment of empirical models describing turbulent boundary layer wall-pressure spectra. Unlike other models presented in literature, the new models are not derived by extending previously existing ones, but are directly built from a given dataset through symbolic regression using a machine...

This paper investigates the application of flow-permeable materials as a solution for reducing jet-installation noise. Experiments are carried out with a flat plate placed in the near field of a single-stream subsonic jet. The flat plate is modular and the solid surface near the trailing edge can be replaced with different flow-permeable inserts, s...

The low-speed fans used for automotive engine cooling contribute to a significant part of the global noise emitted by the vehicle. A low-order sound-prediction methodology is developed considering the blade sweep-angle effect on the acoustic predictions of the turbulence-impingement and the trailing-edge noise-generating mechanisms. We modeled thes...

A possible strategy for the reduction of the aeroacoustic noise generated by turbulence interacting with a wing profile, also referred to as leading-edge noise, is represented by the implementation of a porous medium in the structure of the airfoil. However, the physical mechanisms involved in this noise mitigation technique remain unclear. The pre...

An automotive cooling module working at three different operating conditions is investigated using a microphone array method. Experiments on an open rotor and on a full module configurationswere conducted in theALCOVES anechoic chamber of the von Karman Institute for Fluid Dynamics, Belgium. The acoustic data are post-processed using the ROtating S...

Inverse methods are gaining relevance in the aeroacoustic community for their capability to accurately localize and quantify noise sources. Indeed, since modern aircraft are more targeted to the reduction of fuel consumption, and very often some design choices, like Open Rotor (OR) propulsion systems, cause excessive acoustic emissions, accurate kn...

The analysis of porous materials for aeroacoustic noise mitigation requires high-fidelity numerical tools to simulate the sound propagation and interaction in porous media. The manuscript presents the calibration and validation of a direct-hybrid LES/CAA method used to model the aerodynamically generated sound. The porous micro-structures are model...

Most acoustic imaging methods assume the presence of point sound sources and, hence, may fail to correctly estimate the sound emissions of distributed sound sources, such as trailing-edge noise. In this contribution, three integration techniques are suggested to overcome this issue based on models considering a single point source, a line source, a...

Dedicated numerical simulations of vortex-nozzle interaction indirect noise in solid rocket motors (SRMs) are presented. It is assumed that the flow in the nozzle and hence the sound radiation is not significantly influenced by the global acoustic oscillation of a SRM. Therefore, the study is limited to the acoustic response of a semi-infinite pipe...

In HVAC or domestic appliance applications, industrial fan noise is usually characterized under uniform inflow profile. However, those ideal conditions are rarely met when the fan is installed in its final product. The fan is often in the wake of an obstacle or after a bend, which causes non-uniform ingested flow. Under those distorted inflow condi...

The noise production by ducted single- and double-diaphragm configurations is simulated using a stochastic noise generation and radiation numerical method. The importance of modeling correctly the anisotropy and temporal de-correlation is discussed, based on numerical results obtained by large eddy simulation. A new temporal filter is proposed, des...

This paper presents the shape optimization of the blades of a contra-rotating fan according to aerodynamic, structural and aeroacoustic criteria. The prediction of wake-interaction and trailing-edge noise emission is integrated into the optimization process by means of RANS-based hybrid methods. These methods split the description of the flow field...

Vortex driven sustained pressure pulsations in large solid rocket motors (SRMs) present an analytical modeling challenge, particularly when finite limit cycle amplitudes predictions are aimed for. The need for analytical models of these pulsations in SRMs is discussed. Two modelling strategies are reviewed: the energy balance and Culick’s lumped mo...

This paper compares several approaches for the prediction of the noise emitted by a NACA0012 airfoil at 0∘ and 4∘ of angle of attack and a Reynolds number Re=1.5×106. Amiet's semi-analytical model for trailing-edge noise is combined with two-dimensional Reynolds-Averaged Navier-Stokes (RANS) computations. The wall-pressure spectrum, which constitut...

Shock-cell noise occurs in aero-engines when the nozzle exhaust is supersonic and shock-cells are present in the jet. In commercial turbofan engines, at cruise, the secondary flow is often supersonic underexpanded, with the formation of annular shock-cells in the jet and consequent onset of shock-cell noise. This paper aims at describing the design...

The present study was devoted to the development and application of a remote microphone technique for aeroacoustic measurements in large aerodynamic wind tunnels. In this technique, the microphone and its connecting line to the sensing port are fitted within an aerodynamically streamlined fairing. A model-based calibration method was applied to acc...

The noise generated by a ducted diaphragm configuration, taken in this paper as a prototype aeroacoustic system, is investigated experimentally using a two-port source identification method [Lavrentjev, Åbom, and Bodén (1995) J. Sound Vib. 183, 517−531]. The method requires successively the determination of the so-called passive scattering properti...

The paper presents an investigation of flow and noise produced by the generic fan of an environmental control system installed in a circular duct, with a focus on the evaluation of the effect of mean flow distortions and elevated turbulence levels upstream of the fan, which are here created by replacing a baseline smooth bell-mouth duct inlet by in...

This work will illustrate the multi-objective shape optimization of a counter-rotating fan achieved through the exploration of a high-dimensional design space with an evolutionary algorithm. The approach is multidisciplinary, involving aerodynamics, aeroacoustics and structural mechanics in the definition of the objective functions and of the const...