Efficient Computation of Spinning Modal Radiation Through an Engine Bypass Duct

Abstract

The aim of this work is to accurately and efficiently predict sound radiation out of a duct with flow. The sound propagation inside a generic engine bypass duct, refractions by the shear layer of the exhaust flow, and propagation in the near field are the main focus of the study. The prediction uses either a modified form of linearized Euler equations or an alternative model based on acoustic perturbation equations, which were extended to cylindrical coordinates. The two models were compared on a canonical case of sound propagation out of a semi-infinite duct with flow. Good agreements between the predictions were achieved. The more general case of a generic aircraft engine bypass duct with flow was then investigated with the technique of adaptive mesh refinement to increase the computational efficiency. The results show that both linearized Euler equations and acoustic perturbation equations models can predict the near-field sound propagation and far-field directivity. The acoustic perturbation equations model, however, is more adaptive for its suitability to an arbitrary background mean flow.

Sound Radiation from a Generic Bypass Duct with Bifurcations

“…To compare with the 2.5D APE shown above, the revised 2.5D LEE 2 is also presented in the cylindrical coordinates as A detailed derivation of the 2.5D LEE and the 2.5D APE can be found in Zhang et al 2 and Huang et al 3 . The robustness and accuracy of this treatment were demonstrated through a comparison with analytical solutions using benchmark test cases 2 .…”

“…Inflow and outflow buffer-zones 2 are placed in the inflow and outflow areas to minimize possible spurious wave reflections at the computational boundaries. The inflow buffer-zone also acts as a spinning mode input region with the boundary conditions, which can be found in literatures [2][3] . A periodic boundary condition is applied at the boundaries in the circumferential direction except the bifurcation section.…”

“…Accurate simulation of noise propagation within the engine duct and estimation of far field noise radiation are necessary to provide useful numerical tools for development of noise attenuation methods. A significant amount of research has been undertaken to develop computational methods for engine noise problem using either frequency domain 1 or time domain method [2][3] . For cases with an axisymmetric mean flow environment, a two-and-half dimensional (2.5D) linearsied Euler equations (LEE) model 2 was used in previous works to solve three-dimensional (3D) spinning mode duct radiation problems on a two-dimensional (2D) domain.…”

“…The APE model removes vortical modes and thus suppresses numerical instabilities in the sheared flow. A 2.5D APE model was used in the literature 3 for duct cases with an axisymmetric mean flow environment.…”

Numerical Investigation on Vortex‐Structure Interaction Generating Aerodynamic Noises for Rod‐Airfoil Models

“…There are mainly four types of numerical aeroacoustic prediction methods [5], including the pure theoretical method [6], the semiempirical method [7], the direct numerical method, and the hybrid method [3,8]. In particular, the Lattice-Boltzmann-Method (LBM) has shown being a very promising technique for far field aeroacoustic prediction (Benjamin Duda, Ehab Fares, 2017), such as LAGOON landing-gear configuration [9] and Jet-plate interaction noise [10].…”