The goal of this paper is to perform a detailed analysis of the hydrodynamic near field and acoustic far field of a NACA 64-618 airfoil with and without serrations. The impact of serrations is investigated across different airfoil angles of attack and serration flap angles. The natural boundary-layer transition cases 6 and 7 of the AIAA Benchmark Problems for Airframe Noise Computations V Workshop Category 1 are considered as benchmark for the straight edge cases. The numerical simulations are performed using the fully explicit, transient, and compressible lattice Boltzmann equation implemented in the computational fluid dynamics/computational aero-acoustics (CFD/CAA) solver SIMULIA PowerFLOW®. The acoustic far field is obtained by using the Ffowcs-Williams and Hawkings integral solution applied to the airfoil surface. A mesh resolution study is performed on the straight trailing-edge cases to demonstrate the grid independence of the numerical solution. The numerical results compare favorably against the experimental data. The impact of the serration flap angle on the effectiveness of sawtooth serrations in reducing noise is investigated by considering three different serration flap angles. It is found that the serration flap angle primarily affects the trailing-edge noise reduction through a modification of 1) the effective angle at which the turbulent structures are convected over the serrated edge; 2) the convection velocity and spanwise coherence length along the serration; and 3) the intensity of the hydrodynamic wall-pressure fluctuations that are scattered along the serrated edge. The first and last phenomena are expected to play the most important role on the far-field noise reduction.@en

Passive flow separation control with vortex generators (VG) is actively used over the wind turbine blade. In this paper, the effect of vortex generators is simulated on a full-scale 2-blade wind-turbine tested at the National Renewable Energy Laboratory. The simulation is performed using Very-Large-Eddy/Lattice-Boltzmann method (VLES/LBM). The analysis focuses on the effect of vortex generators on the aerodynamic performance and far-field noise. The simulation results without vortex generators are compared with the experimental results, reaching good agreement. The vortex generators produce counter-rotating vortices in the wake which effectively delay flow separation, leading to better aerodynamic performance. The acoustic analysis indicates that the dominant noise sources are the tonal noise produced by the flow separation and the turbulent-boundary-layer trailing-edge noise. Similar noise levels are obtained for the configurations with and without vortex generators.

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A hybrid lattice Boltzmann method–very-large-eddy simulation (LBM-VLES) solver for high-speed nonisothermal subsonic flows is used to simulate the unsteady jet flow exhausting from a single axi-symmetric nozzle, as well as the associated noise spectra and directivity. The jet exit Mach number and temperature ratio are set according to three representative operating conditions from the NASA SMC000 experimental campaign. The farfield noise is computed through a Ffowcs Williams and Hawkings analogy applied to a fluid surface encompassing the jet plume. Both time- and frequency-domain formulations are used, the latter in combination with an azimuthal Fourier transform of the linear source terms to analyze the contribution of the different azimuthal components. A resolution study is carried out for both aerodynamic and acoustic results. The near- and far-field results confirm that the underlying flow features and noise mechanisms are fully represented by the numerical solution. A wavelet decomposition technique is applied to analyze the source mechanisms for a heated core case. This is achieved by separating the coherent flow motion from the chaotic perturbations in the turbulent flows. Finally, a frequencydomain integral formulation is used to analyze the acoustic far-field of the two segregated components. @en

An investigation of the effects of free-stream on jet-installation noise is performed using a numerical solver based on the lattice-Boltzmann method. In order to simulate a realistic configuration, a high-lift wing comprised by a main element and a deployed flap (MD30P30N) is placed in the vicinity of a dual-stream engine (GE90-94B). The engine operating parameters are used as inputs to generate realistic exhaust flows. Far-field noise spectra from the isolated and installed jets, obtained through the Ffowcs-Williams and Hawkings analogy, are compared for different polar angles. In the absence of free-stream, the results show a low-frequency noise amplification, occurring mainly upstream of the jet axis. This noise increase is due to a dipole source at the flap trailing-edge, where hydrodynamic waves from the jet scatter as sound to the far-field. With free-stream, the wing produces a downward flow, which deflects the jet plume. There is a consequent change on the shear layer turbulence characteristics, which is responsible for altering the far-field spectral shape and directivity pattern of the overall configuration. Through a wavelet decomposition of the near-pressure field, coherent and chaotic fluctuations are splitted. Near-field spectra show the change in amplitude of fluctuations of coherent structures due to free-stream, which are in agreement with the farfield results. @en