Acoustic response of structured and randomized porous blunt trailing edges subject to turbulent boundary layers.

The attachment of porous media to a blunt trailing edge (TE) can significantly suppress vortex shedding processes and the related tonal noise, yet the near-wall and internal flow fields of porous media are difficult to analyze experimentally and rely on numerical simulations to elucidate the internal flow features. A structured porous trailing edge (SPTE) has been recently designed that follows a methodology of a structured porous coated cylinder. The SPTE acoustic response was compared against randomized porous media with 10 and 30 pores/in.

Efficient prediction of airborne noise propagation in a non-turbulent urban environment using Gaussian beam tracing method.

This paper presents a noise propagation approach based on the Gaussian beam tracing (GBT) method that accounts for multiple reflections over three-dimensional terrain topology and atmospheric refraction due to horizontal and vertical variability in wind velocity. A semi-empirical formulation is derived to reduce truncation error in the beam summation for receivers on the terrain surfaces. The reliability of the present GBT approach is assessed with an acoustic solver based on the finite element method (FEM) solutions of the convected wave equation.

Simulating the acoustic response of cavities to improve microphone array measurements in closed test section wind tunnels.

Cavities placed along wind tunnel walls can attenuate the turbulent boundary layer (TBL) fluctuations as they propagate into the cavity. Placing microphones within the cavities can thus improve the signal-to-noise ratio of acoustic data. However, standing waves form within these cavities distorting the acoustic measurements.

Toward inclusion of atmospheric effects in the aircraft community noise predictions.

This paper presents an atmospheric propagation model, based on ray acoustics, that accounts for realistic weather conditions in the evaluation of the noise footprint of an aircraft. Noise sources, obtained using the Ffowcs Williams and Hawkings acoustic analogy applied to scale-resolved flow simulation data, are stored on a hemisphere surrounding the vehicle. These noise sources are propagated using a propagation model that takes into account the vertical variability of air temperature and wind velocity.

Role of Polymeric Coating on Metallic Foams to Control the Aeroacoustic Noise Reduction of Airfoils with Permeable Trailing Edges.

Studies on porous trailing edges, manufactured with open-cell Ni-Cr-Al foams with sub-millimeter pore sizes, have shown encouraging results for the mitigation of turbulent boundary-layer trailing-edge noise. However, the achieved noise mitigation is typically dependent upon the pore geometry, which is fixed after manufacturing. In this study, a step to control the aeroacoustics effect of such porous trailing edges is taken, by applying a polymeric coating onto the internal foam structure.