International Journal of Aeroacoustics 

About: International Journal of Aeroacoustics is an academic journal published by SAGE Publishing. The journal publishes majorly in the area(s): Noise & Jet (fluid). It has an ISSN identifier of 1475-472X. Over the lifetime, 529 publications have been published receiving 8718 citations. The journal is also known as: Aeroacoustics.

Noise prediction for increasingly complex jets. Part I: Methods and tests

Abstract: This Part I presents a detailed description of a numerical system built and tested with the final goal of reaching an accuracy of 2-3 dB over a meaningful range of frequencies for airliner engine noise, while having low empiricism and a general-geometry capability. The turbulence is treated by Large-Eddy Simulation with grids of around 1 million points, slightly upwind-biased high-order differencing, and implicit time integration. The code can incorporate boundaries and multi-block grids (thus avoiding the centerline singularity), and capture shocks. The sub-grid scale model is de-activated, because on present grids it strongly interferes with transition in the mixing layer. Without unsteady inflow forcing, the shear-layer roll-up and three-dimensionalization are realistic and reasonably insensitive to the grid. The far-field noise is computed using the permeable Ffowcs-Williams/Hawkings (FWH) formulation without external quadrupoles. The treatment of the disk that closes the FWH surface near the outflow ...

Surface integral methods in computational aeroacoustics—From the (CFD) near-field to the (Acoustic) far-field

Abstract: A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-field CFD results to the acoustic far-field is given. These integral formulations (i.e. Kirchhoff's method, permeable (porous) surface FfowcsWilliams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the far-field sound, instead of the volume integrals required by the traditional acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-field solution in the near field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the far-field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-field CFD data. Both methods can be extended in orde...

Noise Prediction for Increasingly Complex Jets. Part II: Applications:

Abstract: The numerical system described in Part I (Ref. 1) is applied to a variety of cases which increase difficulty, and progress in the direction of the complete simulation of an airliner engine. The grids have on the order of 1 million points. In many cases, the system meets the 2-3 dB accuracy target both in terms of directivity and of spectrum, up to a Strouhal number of about 1.5. The jet Mach number is varied from 0.3 to slightly supersonic with under-expansion, generating shock cells and greatly increasing side-line noise. For heated jets, the cross-effect between the acoustic Mach number and the temperature is correctly reproduced. Jets placed in a co-flowing stream with velocity up to 60% of the jet's are studied and found to sustain natural transition without unsteady forcing; the noise trends are correct. Finally, "synthetic chevrons" are added by altering the inflow conditions, and found to reduce low-frequency noise while increasing mid-frequency noise. In total, about fifteen meaningfully different...

Coupling of integral acoustics methods with LES for jet noise prediction

Abstract: This study is focused on developing a Computational Aeroacoustics (CAA) methodology that couples the near field unsteady flow field data computed by a 3-D Large Eddy Simulation (LES) code with various integral acoustic formulations for the far field noise prediction of turbulent jets. The LES code employs state-of-the-art numerical schemes and a localized version of the dynamic Smagorinsky subgrid-scale (SGS) model. The code also has the capability to turn off the SGS model and treat the spatial filter that is needed for numerical stability as an implicit SGS model. Noise computations performed for a Mach 0.9, Reynolds number 400,000 jet using various integral acoustic results are presented and the results are compared against each other as well with those from experiments at similar flow conditions. Our results show that the surface integral acoustics methods (Kirchhoff and Ffowcs Williams - Hawkings) give similar results to the volume integral method (Lighthill's acoustic analogy) at a much lower cost. To the best of our knowledge, Lighthill's acoustic analogy is applied to a Reynolds number 400,000 jet at Mach 0.9 for the first time in this study. The distribution of Lighthill sources that radiate noise in the direction of various observer locations is evaluated. A source decomposition shows significant cancellations among the individual components of the Lighthill source.

Extensions and limitations of analytical airfoil broadband noise models

Abstract: The present paper is a state-of-the-art of a special class of analytical models to predict the broadband noise generated by thin airfoils in a flow, either clean or disturbed. Three generating mechanisms are addressed, namely the noise from the impingement of upstream turbulence called turbulence-interaction noise, the noise due to the scattering of boundary-layer turbulence as sound at the trailing edge for an attached flow called trailing-edge noise, and the noise generated due to the formation of a coherent vortex shedding in the near wake of a thick trailing edge, called vortex-shedding noise. Different analytical models previously proposed for each mechanism are reviewed, as declinations of the same basic approach inherited from the pioneer work performed by Amiet in the seventies and based on an extensive use of Schwarzschild's technique. This choice is only an alternative to other models available in the literature and is made here for the sake of a unified approach. Issues dealing with the input d...