Validating Large-Eddy Simulation for Jet Aeroacoustics

Abstract

Engineers charged with making jet aircraft quieter have long dreamed of being able to see exactly how turbulent eddies produce sound, and this dream is now coming true with the advent of large-eddy simulation. Two obvious challenges remain: validating the large-eddy-simulation codes at the resolution required to see the fluid–acoustic coupling, and the interpretation of the massive data sets that are produced. This paper addresses the former, the use of advanced experimental techniques such as particle image velocimetry and Raman and Rayleigh scattering, to validate the computer codes and procedures used to create large-eddy-simulation solutions. This paper argues that the issue of accuracy of the experimental measurements be addressed by cross-facility and cross-disciplinary examination of modern data sets along with increased reporting of internal quality checks in particle image velocimetry analysis. Furthermore, it argues that the appropriate validation metrics for aeroacoustic applications are increasingly complicated statistics that have been shown in aeroacoustic theory to be critical to flow-generated sound, such as two-point space-time velocity correlations. A brief review of data sources available is presented along with examples illustrating cross-facility and internal quality checks required of the data before they should be accepted for validation of large-eddy simulation.