Low-Speed Turbofan Aerodynamic and Acoustic Prediction with an Isothermal Lattice Boltzmann Method

Abstract

The objective of this paper is to assess the capability of the isothermal lattice Boltzmann method (LBM) to correctly capture aerodynamic and acoustic features from a low-speed turbofan. The evaluation is done on the Advanced Noise Control Fan model developed by NASA Glenn Research Center. An extensive comparison of the measured and computed aerodynamic results is presented for the first time on this configuration. The trends are well captured, but quantitative discrepancies are observed for some variables, leading to lower fan performance values in the simulations. This last point was also observed in the previous related studies, but remained unexplained. By validating in parallel the LBM aerodynamic results with a Reynolds-averaged Navier–Stokes simulation provided by the database, a likely uncertainty of the absolute values of some variables in the experimental mean flow data is shown (a result of the intent that experimental data were not acquired with absolute levels as an objective). Direct in-duct and far-field acoustic results are also investigated, taking advantage of the low-dissipative characteristics of the LBM. A good agreement with the measurements in terms of broadband noise is obtained, but the low frequencies tend to be overestimated. For the tonal noise, if the expected acoustic modes are recovered, quantitative differences are observed. Predictions based on a hybrid method, where the acoustic sources computed by the LBM are propagated analytically using Goldstein’s analogy (Aeroacoustics, McGraw–Hill, New York, 1976), are also made and compare well with the direct predictions, thus proving the correct propagation of acoustic waves by the solver.