Noise predictions of the advanced noise control fan model using lattice Boltzmann method and Ffowcs Williams–Hawkings analogy

Abstract

The lattice Boltzmann method (LBM) is applied to simulate the complete three-dimensional transient flow and noise generated on the Advanced Noise Control Fan (ANCF) geometry. The ANCF is a model developed by NASA Glenn composed by a rotor-stator system enclosed by a duct. The experimental noise spectra provided by NASA at 30 microphones around the fan are used to validate the results obtained with the LBM. Overall, the predicted sound spectra pattern and the main tonal frequencies agree well with the noise measurements; in terms of tonal noise levels, the agreement varies depending on the frequency and microphone position. The noise at the 30 microphone positions is also computed by employing the porous Ffowcs Williams and Hawkings (FW-H) formulation with noise sources located on two integral surfaces placed at the ANCF openings. The good agreement obtained between the sound levels calculated with the FW-H formulation and those computed by the LBM show that the FW-H analogy may be applied in place of the LBM numerical simulation. In addition, the FW-H formulation is applied to compute the sound generation with sources located on different physical surfaces of the ANCF model such as the rotor, stator, hub, and nacelle, procedure known as noise source breakdown. A comparison of the FW-H results applied on different surfaces of the ANCF model with the noise computed by the LBM shows that most of the tonal noise levels observed at the far-field microphones (predicted by the LBM simulation) correspond to the noise sources generated on the stator vane surfaces. Such a study of the noise sources breakdown also evidences the interaction effect between the rotor and the stator, whose mechanism is the main contributor to the tonal noise generation content.

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

“…The broadband noise is quite well reproduced in the study of Mann et al [13] but tends to be underestimated by 5 to 10 dB in the one of Orselli et al [15]. In both studies, the tonal noise is importantly overestimated with gaps of 5 to 20 dB at the Blade Passing Frequency (BPF) and its first two harmonics.…”

“…Turbomachinery applications using an LBM solver started to be studied since 2012 [4,9,[13][14][15][16]. To the authors knowledge, only results obtained with the PowerFLOW code have been published up to now.…”

“…The NASA Glenn Research Center provided many experimental data for both configurations thus allowing for an advanced validation of aerodynamic and acoustic features. The first studies are dedicated to the ANCF configuration because its low fan-blade tip Mach number at nominal speed (0.34) is compatible with the use of an isothermal LBM (D3Q19 scheme) [13,15]. The aerodynamics is not deeply investigated in these studies, despite some assessment of the total pressure and velocity radial profiles in the inlet and some considerations about the mass flow rate.…”

“…There are even the results of a Reynolds-Averaged Navier-Stokes (RANS) simulation in the database, which might also be used for aerodynamic validation as it is a robust and mature technique for mean flow prediction. Compared to the previous studies on the ANCF configuration [13,15], a deeper analysis on aerodynamics will be provided. Indeed, if the generation and convection of turbulent structures and the propagation of acoustic waves are not expected to be affected by the isothermal assumption, the effect on the mean aerodynamics is less clear.…”

Accurate Computation of Airfoil Flow Based on the Lattice Boltzmann Method

“…Computation results from the LBM can reflect the fine structure of the flow field and provide accurate numerical results for the computation of aerodynamic noise. Long-term research shows that the LBM is indeed suitable for the computation of aerodynamic noise [26,27].…”