Effect of porous material on trailing edge sound sources of a lifting airfoil by zonal Overset-LES

On the noise reduction of a porous trailing edge applied to an airfoil at lifting condition

“…11, it is possible to conclude that the noise reduction mechanisms of the porous TE remain identical at different flow conditions, at least within the present range of AoA and Reynolds number. The metal-foam TE in the present investigation has a lower scattering efficiency compared to the solid one 11,19 due to the modification of phase relationships among noise sources at the porous medium surface; this mechanism has also been implied in several analytical studies. 40,46 The noise attenuation capability of the porous TE has been previously associated with the interaction between surface pressure fluctuations across the porous TE, which is referred to as the pressure release process.…”

“…The pressure field beneath the boundary layer is mainly produced by eddies at convective wavenumber 50,54 that is proportional to f =U c , where U c is the convection velocity. Ananthan et al 11 argued that the porous TE promotes a lower convection velocity that can be related to noise attenuation. To verify this, the convection velocity at the trailing edge region is computed using a space-time correlation of surface pressure fluctuations R pp as follows: where pðx; tÞ is the surface pressure fluctuations at a given location x and at time t, and Dx and Dt are the spatial and temporal separations, respectively.…”

“…22,23 In a different approach, referred to as the volume-averaging method, the internal volume of the porous medium is replaced by an equivalent fluid region, where additional physical conditions are imposed to take the porous media properties (e.g., permeability and porosity) into account. 11,24 This technique has been employed previously by the authors 14 for studying a National Advisory Committee for Aeronautics (NACA) 0018 equipped with a metal-foam TE insert, replicating the experimental setup of Rubio Carpio et al 10 They concluded that, in addition to the smoother impedance transition at the TE, the destructive interference between the noise emitted by the distributed sound sources on the porous insert contributed toward noise attenuation.…”

“…3 Considering that turbulent flows are common in industrial applications, various investigations have been performed to achieve TBL-TE noise mitigation, such as by performing airfoil shape optimization 4 and by applying TE addons, such as serrations [5][6][7][8] or permeable/porous TE inserts. [9][10][11] Permeable TE inserts, in particular, have been demonstrated to be promising passive noise mitigation devices due to their ability to produce substantial noise reduction, with relatively small adverse aerodynamic impact. [12][13][14][15] These inserts tend to produce larger noise reduction when materials with higher permeability and porosity are employed, although this comes at the cost of aerodynamic penalty.…”

Numerical analysis of a 3-D printed porous trailing edge for broadband noise reduction

“…2017; Ananthan et al. 2020). Unlike serrations, which are often manufactured as TE add-ons (or TE extensions), porous materials are usually employed as inserts that replace the aft section of aerofoils.…”