Acoustic modeling of perforated plates with bias flow for Large-Eddy Simulations

Abstract

The study of the acoustic effect of perforated plates by Large-Eddy Simulations is reported. The ability of compressible Large-Eddy Simulations to provide data on the flow around a perforated plate and the associated acoustic damping is demonstrated. In particular, assumptions of existing models of the acoustic effect of perforated plate are assessed thanks to the Large-Eddy Simulations results. The question of modeling the effect of perforated plates is then addressed in the context of thermoacoustic instabilities of gas turbine combustion chambers. Details are provided about the implementation, validation and application of a homogeneous boundary condition modeling the acoustic effect of perforated plates for compressible Large-Eddy Simulations of the flow in combustions chambers cooled by full-coverage film cooling.

LES for the Evaluation of Acoustic Damping of Effusion Plates

“…The inlet patch is instead placed closer to the wall and the bias flow is generated by a totally reflecting velocity inlet. Such a scheme is equivalent to that exploited by Mendez and Eldredge [5] and Andreini et al [6].…”

“…In case of desired mean cross-flow, it is generated across the two patches with normal vector oriented in the X direction, called in the following X+ and X-. This domain definition enables to represent an infinite pattern of holes in both the stream and tangential direction and was already implemented for similar purposes in [5,31]. Surfaces Y + and Y −, with normal vector orthogonal to the eventual main flow, reproduce a simple in-line arrangement as better reported in Fig.2(a).…”

“…Moreover experiments and other computational predictions generally perform such analysis investigating one frequency at the time [5], it is hence fundamental, to compare the responses of pure and multi-tonal signals in order to evaluate the effects of spurious forcing.…”

“…Despite the fact that simple numerical models to characterize those screens have been proposed [2][3][4] and successfully applied [1,5,6] also to relatively complex set-up under a wide range of flow condition, detailed CFD simulations [7][8][9] and large experimental campaigns [10][11][12][13] are more and more performed to increase the knowledge of the mechanisms ruling the phenomenon and expand the database of available geometries and flow conditions. Surprisingly the use of fully 3D computational technique did not push researchers to investigate more complex models including globally three dimensional flow and acoustic conditions.…”

“…Surprisingly the use of fully 3D computational technique did not push researchers to investigate more complex models including globally three dimensional flow and acoustic conditions. Most of the reported works dealt with the basic set-up in which an orthogonally perforated plate with relatively low bias flow is reflecting a normally incident acoustic wave in absence of any mean flow in the liner itself [5,7,8]. This situation is however not fully realistic on actual combustor liners since perforations are usually inclined, the combustor is subjected to a mean flow and the main acoustic waves are travelling parallel to the plate.…”