Turbofan Broadband Noise Prediction Using the Lattice Boltzmann Method

Abstract

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

Hermite regularization of the lattice Boltzmann method for open source computational aeroacoustics

“…The LBM turns out to be computationally more efficient with respect to the traditional NS-LES for low Mach number flow. Very promising are also the recent results obtained for the prediction of a complete turbofan engine noise 6,5 and full aircraft airframe noise. 20 All these examples clearly demonstrate the capability of the LBM-LES in solving aeroacoustic problems with complex geometries (in the subsonic regime) while remaining computationally efficient.…”

“…1,2,3 More recently, there has been a growing interest in the Lattice Boltzmann method (LBM) to address aeroacoustic problems of practical relevance. 4,5,6 This method instead of directly solving the the Navier-Stokes equations (NS) models fluids through the Boltzmann equation which describe the time evolution of velocity density distribution function (see for instance Chopard et al 7 ). The main differences with the NS solvers is the absence of non-linearity in the convection term and the fact that there is no need of an analytic description of the grid metrics.…”

“…In particular, most of these realistic applications have been solved thanks to the commercial software PowerFLOW (http://www.exa.com/), developed by scientists that contributed significantly to the establishment of the LBM in automotive and aerospace engineering fields (e.g. Casalino et al 5 ). Nonetheless, the source code of this sophisticated software is not available to the end-user.…”

Free-Stream Effects on Jet-Installation Noise of a Dual-Stream Engine

“…The methodology described above is implemented in the commercial software Simulia PowerFLOW 6-2019. This software has been also used and validated for aero-engine aeroacoustic applications to predict fan broadband noise in subsonic [25,26] and transonic conditions [27]. A validation study for an isolated jet (SMC000) has been accomplished by van der Velden et al [15], showing a very good agreement with experimental results, as well as Nickerson et al [17] for an isolated jet with chevron nozzles.…”

Analysis of fan-stage gap-flow data to inform simulation of fan broadband noise

“…More direct simulation methods for predicting the broadband noise have also been presented [21][22][23][24][25][26]. In these methods, the acoustic pressure at the inlet and/or exhaust planes or even in a region upstream or downstream of the engine are computed.…”