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.

Active control of airfoil turbulent boundary layer noise with trailing-edge blowing.

Large Eddy Simulation (LES) and Ffowcs Williams-Hawkings acoustic analogy are performed to study the effect of trailing-edge blowing on airfoil self-noise. Simulations were conducted using a National Advisory Committee for Aeronautics 0012 airfoil at zero angle of attack and a chord-based Reynolds number of 4 × 10 5. The aerodynamic and aeroacoustic characteristics of the baseline airfoil were thoroughly verified by comparison with previous numerical and experimental data.

An acoustic investigation of non-uniformly structured porous coated cylinders in uniform flow.

The application of a porous coating to a smooth cylinder placed in uniform flow can reduce its vortex shedding tone and overall sound pressure level. The responsible noise generation mechanisms are not fully understood nor has an optimal porous coating type been presented. Structured Porous Coated Cylinders (SPCCs) have been recently investigated as an alternative to randomized porous coated cylinders that use metal foam or polyurethane.

An array pairing method for localizing distributed sources by acoustic beamforming.

An acoustic beamforming concept is presented that alleviates some misrepresentation caused by deconvolution algorithms that can oversimplify distributed sources as a series of point sources. In the Array Pairing Method (APM) an initial array beamforms the acoustic source, then an iterative randomized array is calculated whereby the square-rooted product of the beamformer output possesses a minimum product of Maximum Sidelobe Level (MSL) and Main Lobe Width (MLW). A single and distributed source simulation and a single and dual speaker experiment using the APM reveal significant improvements in MSL and MLW and resolution in the distributed source region.

Structured Porous Material Design for Passive Flow and Noise Control of Cylinders in Uniform Flow.

Cylindrical bodies in uniform flows can be coated with a porous medium as a passive flow and noise control method in an effort to reduce the acoustic effects of vortex shedding. To date, the employed open-cell porous materials typically possess a randomized internal structure. This paper presents the design and validation of a novel 3-D printed structured porous coated cylinder that has significant flexibility, in that the porosity and pores per inch of the porous coating can be modified independently and relatively easily.

Adaptive array reduction method for acoustic beamforming array designs.

This letter presents a modification to a very recent iterative microphone removal array design process, called the Array Reduction Method (ARM). The ARM iteratively reduces an array based on the product of sidelobe and main lobe criteria, yet the main lobe may become distorted and the beamformer output can disproportionately favor one of the criteria. The Adaptive Array Reduction Method presented here uses the derivative estimates of the maximum sidelobe level and main lobe width with respect to the number of microphones removed, and the distortion of the main lobe during iteration, to produce an improved source image map.