Adrien Mann

Advanced Noise Control Fan Direct Aeroacoustics Predictions using a Lattice-Boltzmann Method

A Lattice-Boltzmann Method (LBM) based approach is used to perform transient, explicit and compressible CFD/CAA simulations on the Advanced Noise Control Fan (ANCF) configuration. The complete 3-D ducted rotor/stator model including all the geometrical details and the truly rotating rotor is simulated. Detailed near and far-field measurements conducted at the NASA Glenn research center are used to validate the simulation results. The measured and predicted sound pressure levels at the far-field microphones are compared and both show the presence of broadband noise and sharp peaks which frequencies depend on the number of rotor blades and the angular velocity of the rotor. The 3-D duct acoustics modes observed in experiments are also captured in the 3-D transient CFD/CAA calculation and detailed analyses of the results are presented. The main circumferential modes predicted from the number of rotor blades and stator vanes are recovered in both experimental and simulation modal decompositions.

Towards Lattice-Boltzmann Prediction of Turbofan Engine Noise

The goal of the present paper is to report verification and validation studies carried out by Exa Corporation in the framework of turbofan engine noise prediction through the hybrid Lattice-Boltzmann/Ffowcs-Williams & Hawkings approach (LB)-(FW-H). The underlying noise generation and propagation mechanisms related to the jet flow field and the fan are addressed separately by considering a series of elementary numerical experiments. As far as fan and jet noise generation is concerned, validation studies are performed by comparing the LB solutions with literature experimental data, whereas, for the fan noise transmission through and radiation from the engine intake and bypass ducts, LB solutions are compared with finite element solutions of convected wave equations. In particular, for the fan noise propagation, specific verification analyses are carried out by considering tonal spinning duct modes in the presence of a liner, which is modelled as an equivalent acoustic porous medium. Finally, a capability overview is presented for a comprehensive turbofan engine noise prediction, by performing LB simulation for a generic but realistic turbofan engine configuration.

Characterization of Acoustic Liners Absorption using a Lattice-Boltzmann Method

The impedance of acoustic liners is predicted using lattice-Boltzmann fluid dynamics simulations. The complete three-dimensional geometry of liners, which corresponds to the combination of micro-perforated sheets, honeycomb cavities and porous materials are directly characterized through a numerical setup that reproduces a Kundts tube and realistic liner samples. In a first step, a mesh resolution study is performed for a One Degree of Freedom (1-DOF) liner in order to show the convergence of the deducted value of the acoustic impedance with the grid size. In a second step, the influence of all the geometric parameters of the liner is predicted for 1-DOF, Two Degree of Freedom (2-DOF) and Bulk Absorber (BA) liners. The predicted impedance is compared with two analytical impedance models available in the literature.

Turbofan Broadband Noise Prediction Using the Lattice Boltzmann Method

The present work describes a numerical reproduction of the 22-in source diagnostic test fan rig of the NASA Glenn Research Center. Numerical flow simulations are performed for three different rotor...

Airfoil Tip Leakage Aeroacoustics Predictions using a Lattice Boltzmann Based Method

The noise produced by rotating systems such as fans and turbo machines is of growing importance in the academic and engineering communities. The prediction and understanding of the physical mechanisms associated with noise generation are required in order to develop innovative solutions able to efficiently reduce radiated acoustics levels. The flow-induced noise generation mechanisms related to rotating devices are various and complex, and one of them is related to the blade tip flow. The tip flow noise, or tip leakage noise, is particularly important for free-tip configurations, for which the tip flow induced by the pressure gradient between the suction and pressure sides can be particularly intense. The experimental investigation of this mechanism is practically challenging. Consequently, a simplified non-rotating representative configuration has been proposed, and has been previously investigated experimentally. In this paper, transient, compressible, and time-explicit Computational Fluid Dynamics/Computational Aero-Acoustics (CFD/CAA) simulations of an airfoil tip leakage flow for this simplified geometry are performed using a Lattice Boltzmann Method (LBM) based approach. The studied configuration is a NACA 5510 airfoil profile at high Reynolds number flow conditions, for which a variable size gap is introduced between the airfoil and one of the end plates, modeling the tip gap encountered in free-tip fans. First, the simulation results are compared with experimental results to validate the numerical approach. Further investigation of the numerical results underlines the connection between the tip vortex structures and noise radiation, including a parametric study on the Angle of Attack (AoA) and the tip gap width.

Direct Transmission Loss Calculation of Simplified Muffler Configurations Using a Lattice-Boltzmann Method

Lattice-Boltzmann Method (LBM) is broadly used for the simulation of aeroacoustics problems. This time-domain CFD/CAA approach is transient, explicit and compressible and offers an accurate and efficient solution to simultaneously resolve turbulent flows and their corresponding flow-induced noise radiation. Some examples of applications are ground transportation wind-noise problems, buffeting, Heating, Ventilation, and Air Conditioning (HVAC), fan noise, etc. As shown in previous studies, LBM can also be used to accurately handle linear acoustics problems if the source of noise is not a flow but a simple acoustic source. This set of capabilities makes LBM a suitable candidate for evaluating the acoustics performances of exhaust systems and mufflers.Compared to other traditional acoustics methods, LBM presents the advantage to skip tedious volume meshing operations since the mesh generation is fully automatic. Furthermore, considering that all geometrical details are included in the simulation domain and that LBM is explicit, high frequencies mechanisms up to 10–20 kHz can be captured. The upper frequency limit is indeed solely driven by the spatial resolution used to discretize the system.In this paper, three academic 3-D geometries representative of production muffler systems are studied. Transmission Loss (TL) measurements are performed on three configurations and these experiments are reproduced numerically with LBM.The experimental setup is described in a first part and the numerical details are given in a second part and third part. In particular, the method used to calculate the TL in the simulation and the convergence of the results with respect to the spatial resolution are shown. In a third part, the simulations are compared to the TL measurements and a numerical investigation of the effect of geometry details on the simulated results is proposed. This study highlights the sensitivity of acoustics measurements to geometry details.Copyright

Laminar boundary layer instability noise

A direct numerical simulation is performed of the flow field around a modern controlleddiffusion airfoil within an anechoic wind-tunnel at 5◦ incidence and a high Reynolds number of 1.5 × 10. The simulation compares favorably with experimental measurements of wall pessure, wake statistics, and far-field sound. In particular, the simulation captures experimentally observed high-amplitude acoustic tones that rise above a broadband hump. Both noise components are related to breathing from a recirculation bubble formed around 65-70% of the chord, and to Kelvin-Helmholtz instabilities in the separated shear layer that yield rollers that break down into turbulent vortices whose diffraction at the trailing edge produces a dipole acoustic field. A linear stability analysis of the mean flow field around the airfoil identifies convective instability in the aft portion of the airfoil where this shedding occurs for frequencies covering the broadband hump, and also provides estimates of the tonal frequencies.