Advanced Noise Control Fan Direct Aeroacoustics Predictions Using a Lattice-Boltzmann Method

Abstract

A Lattice-Boltzmann Method (LBM) based approach is used to perform transient, explicit and compressible CFD/CAA simulations on the Advanced Noise Control Fan (ANCF) configuration. The complete 3-D ducted rotor/stator model including all the geometrical details and the truly rotating rotor is simulated. Detailed near and far-field measurements conducted at the NASA Glenn research center are used to validate the simulation results. The measured and predicted sound pressure levels at the far-field microphones are compared and both show the presence of broadband noise and sharp peaks which frequencies depend on the number of rotor blades and the angular velocity of the rotor. The 3-D duct acoustics modes observed in experiments are also captured in the 3-D transient CFD/CAA calculation and detailed analyses of the results are presented. The main circumferential modes predicted from the number of rotor blades and stator vanes are recovered in both experimental and simulation modal decompositions. Nomenclature M = Mach number f k = k -th BPF harmonic order c b = Rotor blade chord s b = Rotor blade span Δx tip = Tip clearance c v = Stator vane chord d h,up = Upstream hub diameter d h,do = Downstream hub diameter p = Static pressure r = Radial coordinate θ = Azimuthal coordinate x = Axis coordinate t = Time m = Circumferential mode order n = Radial mode order k = x-axis eigenvalue κ = radial eigenvalue J m = Bessel function of the first kind and order m B = Number of fan blades V = Number of stator vanes s = Fan shaft harmonic Ω = Rotation frequency of the fan c 0 2 R 0 = Fan radius ρ 0 = Air density C i = Discrete collision component in the i -th direction c i = Discrete velocity component in the i -th direction f i = Particle distribution function in the i -th direction T = Temperature τ = Relaxation time ν = Kinematic viscosity ∆t = Numerical time step

Numerical Predictions of Turbulence-Cascade Interaction Noise Using CAA with a Stochastic Model

“…and numerical [7,27] methods, and to adjust the turbulent-inflow characteristics from hot-wire measurements or from a Reynoldsaveraged Navier-Stokes computation data.…”

“…These simulations are generally restricted to a radial strip and to a single vane channel by enforcing periodicity conditions, and it should be more considered for capturing the three-dimensional (3-D) turbulent wake behind an isolated rotor blade as investigated, for example, in [6]. Recently, the lattice Boltzmann method (LBM) has been firstly applied to turbomachinery-noise problems with an impressive direct acoustic simulation performed by Exa [7] on the NASA Glenn Research Center's Advanced Noise Control Fan model, including the full rotor-stator stage and the wind-tunnel walls. The LBM technique appears to be a quite promising way to face present limitations in terms of current CPU capabilities.…”

Airfoil Tip Leakage Aeroacoustics Predictions using a Lattice Boltzmann Based Method

“…summations over the set of discrete directions, of the particle distribution function [8][9][10]25,26,28,29,31,32 . LBM is used and validated across many aeroacoustics applications such as automotive wind noise 13 , acoustics propagation 14 , airframe noise 15 , sunroof buffeting 16 , exhaust systems 17 , fan noise [18][19][20][21] and HVAC systems noise [22][23][24] . Further details on LBM can be found in the cited references.…”

“…In this study, the Computational Fluid Dynamics/Computational AeroAcoustics (CFD/CAA) solver PowerFLOW based on the Lattice-Boltzmann Method is used to predict the transient flow field and corresponding flow-induced noise radiation [5][6][7][8][9][10][11][12] . The solver has been successfully applied in numerous industrial analyses, academic validations and investigations such as wind-noise, HVAC, fans, blower and wind-turbine problems [13][14][15][16][17][18][19][20][21][22][23][24] . Wall Pressure Fluctuations (WPF) near the tip gap are the focus of this paper, as the noise-generating mechanisms of interest for fans are expected to correlate to the measurement locations on the blade.…”

Towards Lattice-Boltzmann Prediction of Turbofan Engine Noise

“…The simulation setup was derived from an existing one used in the past to perform pioneering fan noise simulations and analyses. 44,46 Despite the low Mach tip operating condition (∼ 0.33), which is not representative of a real turbofan engine, and the uncertainties associated with some geometry detail in the experimental setup and to the installation of the so-called Inlet Control Device (ICD) around the nacelle intake, the ANCF constitutes a very useful benchmark experiment for the validation of CFD/CAA tools.…”