Assessment of Numerical Tools for the Evaluation of the Acoustic Impedance of Multi-Perforated Plates

Abstract

Multi-perforated liners, commonly employed in Gas Turbine combustors as cooling devices to control metal temperature, are recognized as very effective sound absorbers. Thus, in the innovative lean combustion technology, where the onset of thermoacoustic instabilities represents one of the most important issue, the multi-perforated plates can be exploited both for wall cooling and damping combustion instabilities.1

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].…”

“…The proposed LES methodology is compared to a simplified approach which solve only for the acoustic field inside the liner and model the acoustic impedance of perforated plates with bias flow as an equivalent wall compliance, already presented in [6] and here briefly summarized.…”

“…The aim of this paper is to consider all the above mentioned effects into the same investigation to completely characterize the perforation already investigated with a basic set-up in [6]. In practice the analysis includes the effects of slanted perforation (orthogonal and 30 • holes), of a mean cross-flow and a non normal acoustic forcing as well as a two level analysis on the influence of the Ma b .…”

“…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.…”

“…A systematic validation of the acoustic simulation procedure against both available experiments and lower order numerical tools was already carried out in [6] on simpler reference tests thus the focus of this work will be on the newly introduced technique only. Comparison with results obtained with lumped acoustic procedure (Howe model [18]) is included in the discussion.…”