A direct numerical simulation of the flow field around a controlled-diffusion airfoil within an anechoic wind-tunnel at 5 • incidence and a high Reynolds number of 1.5 × 10 5 is performed for the first time using a Lattice Boltzmann Method. The simulation compares favorably with experimental measurements of wall-pressure, wake statistics, and far-field sound. The simulation noticeably captures experimentally observed high-amplitude acoustic tones that rise above a broadband hump. Both noise components are related to a breathing of a recirculation bubble formed around 65-70% of the chord, and to Kelvin-Helmholtz instabilities in the separated shear layer that yield rollers that break down into turbulent vortices whose diffraction at the trailing edge produces a strong dipole acoustic field. A wavelet analysis of the wall-pressure signals combined with some flow visualization has shown that the flow statistics are dominated by intense events caused by intermittent, large and intense bursting rollers. Several modal analyses of these events are performed on both the wall pressure fluctuations and the span averaged flow field in order to analyse the boundary layer instability which triggers the typical sharp tones over a broadband hump in airfoil noise. A suction side Kelvin-Helmholtz instability is observed to be coupled with a pressure side vortex shedding induced by the sudden transition to turbulence and the blunt trailing edge.

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The present work describes a numerical reproduction of the 22-in source diagnostic test fan rig of the NASA Glenn Research Center. Numerical flow simulations are performed for three different rotor/stator configurations and one rotational speed, representative of an approach operating condition, by using the lattice-Boltzmann solver PowerFLOW. The full stage and nacelle geometries are considered, and results are compared to available measurements. Tripping the rotor blades results in a slightly more accurate noise prediction as a consequence of a more accurate prediction of the velocity fluctuations in the rotor wake over the whole blade span. Fourier circumferential analyses are performed for an intake and a bypass duct section with the intent of explaining the origin of some tonal noise components and comparing the present results to available literature results. Finally, the effects of adding an acoustic treatment in the intake is shown by directly resolving the unsteady flowfield in a single-degree-offreedom honeycomb layer. Nomenclature C mx = axial momentum coefficient c ∞ = freestream speed of sound M ∞ = freestream Mach number R = microphone radial distance u x , u r , u θ = axial, radial, and tangential flow velocity components θ = microphone angular location in the engine symmetry plane ρ ∞ = freestream density

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

The goal of the present paper is to report verification and validation studies carried out by Exa Corporation in the framework of turbofan engine noise prediction through the hybrid Lattice-Boltzmann/Ffowcs-Williams & Hawkings approach (LB)-(FW-H). The underlying noise generation and propagation mechanisms related to the jet flow field and the fan are addressed separately by considering a series of elementary numerical experiments. As far as fan and jet noise generation is concerned, validation studies are performed by comparing the LB solutions with literature experimental data, whereas, for the fan noise transmission through and radiation from the engine intake and bypass ducts, LB solutions are compared with finite element solutions of convected wave equations. In particular, for the fan noise propagation, specific verification analyses are carried out by considering tonal spinning duct modes in the presence of a liner, which is modelled as an equivalent acoustic porous medium. Finally, a capability overview is presented for a comprehensive turbofan engine noise prediction, by performing LB simulation for a generic but realistic turbofan engine