Reducing aerofoil–turbulence interaction noise through chordwise-varying porosity

Abstract

Abstract

Rapid distortion theory of turbulent flow around a porous cylinder

“…2020; Ayton et al. 2021) studies demonstrated the effectiveness of this passive noise-control strategy. However, despite the numerous analyses, the physical mechanisms involved in the noise reduction remain unclear.…”

A Numerical Study on Aircraft Noise Mitigation Using Porous Stator Concepts

“…Unfortunately, to the authors' best knowledge, the optimization procedure for the design and implementation of a permeable LE is still inconclusive, unlike for LE serrations. In fact, novel permeable LE designs are still being actively investigated at the time of writing [14,15,20,21]. Regardless, these studies have shown that permeable LE applications are very promising in both efficacy and versatility aspects.…”

Do we need non-linear corrections? On the boundary Forchheimer equation in acoustic scattering

“…Note also that the nature of this boundary condition still permits the time-harmonic form ∼ e −iωt . Previous theoretical [5] and low-fidelity numerical [11] work concerned with the prediction of aerodynamic noise scattering and absorption by porous materials focuses on the first notion of porosity, perforated plates, as these can be easily described by two parameters; the Rayleigh conductivity, K R , and an open area ratio, α, of the surface. Due to the complexity of a background steady flow interacting with a porous material, these models do not include such a background flow and are purely concerned with acoustic scattering.…”

“…For further simplicity, the models consider the boundary conditions to be linearised to y = 0, thus effectively reducing an aerofoil to a flat plate. Both semi-infinite and finite plate models have been considered this way [5,11]. Experimental findings show that porosity is effective at reducing low and mid-frequency noise, both for perforations and foam-like materials [4,3].…”

“…To implement the non-linear condition, we extend a previous linear boundary collocation method [16,17,11], which represents the solution in terms of local Mathieu function expansions. In the context of the current paper, this method, along with a partitioning of the system according to the different (kinematic and non-linear Forchheimer) boundary conditions, gives rise to a non-linear system of equations (see (3.10)) for the unknown coefficients, which we solve via Newton's method.…”