Relevance of quadrupolar sound diffraction on flow-induced noise from porous-coated cylinders

This paper elucidates the link between the near-wake development of a circular cylinder coated with a porous material in a low Mach-number flow and the related aerodynamic sound attenuation. It accomplishes this by formulating the cylinder flow-induced noise as a diffraction problem. The necessity for such an approach is driven by...

On the mechanisms of jet-installation noise reduction with flow-permeable trailing edges

This paper investigates the mechanisms by which flow-permeable materials provide noise reduction in an installed jet configuration. Numerical simulations are carried out with a flat plate placed in the near field of a single-stream subsonic jet (M_a=0.3 and M_a=0.5). The trailing-edge region of the plate is replaced by...

Jet-installation noise reduction with flow-permeable materials

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...

Experimental investigation of turbulent coherent structures interacting with a porous airfoil

Abstract: 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...

Quantitative criteria to design optimal permeable trailing edges for noise abatement

An experimental study on broadband noise scattered by permeable trailing edges with different pore arrangements is performed. A NACA 0018 airfoil with chord c = 0.2 m is investigated at chord-based Reynolds numbers ranging from 1.4 × 10⁵ to 3.8 × 10⁵ and angles of attack of 0.2 and 5.4 degrees. Noise emission from five...

On the role of turbulence distortion on leading-edge noise reduction by means of porosity

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....

Temperature-activated change of permeable material properties for low-noise trailing edge applications

The present work analyses broadband noise scattering from permeable trailing edges with identical micro-structure but under a change of temperature. Experiments are performed in an anechoic wind tunnel using a NACA0018 airfoil at chord-based Reynolds numbers between 1.88 × 10⁵ and 3.14 × 10⁵ and no incidence. A...

Experimental characterization of the turbulent boundary layer over a porous trailing edge for noise abatement

The hydrodynamic and acoustic fields for a NACA 0018 with solid and porous trailing edge inserts are investigated. The porous inserts, covering 20% of the chord, are manufactured with metal foams with cell diameters of 450 and 800 μm and permeability values of 6 × 10−10 and 2.7 × 10−9 m2. The experiments are performed at a chord-based Reynolds...