in Atlanta, Georgia, USA. The objective of this workshop was to assess the present computational capability in the area of physics-based prediction of different types of airframe noise problems and to advance the state-of-the-art via a combined effort. This documentation summarizes the results from workshop category 1 (BANC-III-1) which focuses on the prediction of broadband turbulent boundary-layer trailing-edge noise and related source quantities. Since the forerunner BANC-II workshop identified some room for improvements in the achieved prediction quality, BANC-III-1 relies on the same test cases, namely 2D NACA 0012 and DU96-W-180 airfoil sections in a uniform flow.Compared to BANC-II particularly the scatter among predictions for the DU96-W-180 test case could be significantly reduced. However, proposed adaptations of previously applied computational methods did not systematically improve the prediction quality for all requested parameters. The category 1 workshop problem remains a challenging simulation task due to its high requirements on resolving and modeling of turbulent boundary-layer source quantities.Downloaded by PURDUE UNIVERSITY on July 26, 2015 | http://arc.aiaa.org |

A numerical model for the exhaust noise radiation problem is presented. In the model, it is assumed that an incoming wave is propagating through the exhaust nozzle, or the fan duct, and radiating outside. The near-field propagation is based on the solution of the linearized Euler equations in the frequency domain: for each wave number, a linearized Euler problem is solved using a finite element method on unstructured grids for arbitrarily shaped axisymmetric geometries. The frequency-domain approach enables the suppression of the Kelvin-Helmholtz instability waves. Moreover, each single calculation, limited to a single frequency, is well suited to the exhaust noise radiation problem in which the incoming wave can be treated as a superposition of elementary duct modes. To reduce the memory requirements, a continuous Galerkin formulation with linear triangular and quadrangular elements is employed and the global matrix inversion is performed with a direct solver based on a parallel memory distributed multifrontal algorithm for sparse matrices. The acoustic near field is then radiated in the far field using the formulation of Ffowcs Williams and Hawkings. Numerical calculations for a validation test case, the Munt problem, and two turbomachinery configurations are compared with analytical solutions and experimental data.

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The main objective of the present work is to investigate the mechanism of trailing-edge airfoil noise. The vorticity associated with the unsteady turbulent structures is scattered by the trailing edge and acoustic waves are generated. It has been recognized that trailing-edge noise can be reduced by introducing sharp sawtooth serrations at the trailing-edge. The flow past a serrated airfoil, with free-stream Reynolds number 6.0 × 10 5 and Mach number M = 0.17, is studied. A compressible Large Eddy Simulation is used for computing the near field, and the far-field acoustic propagation is obtained applying the integral formulation of Ffowcs Williams and Hawkings. The results of the serrated configurations, and its baseline geometry, are compared with the experimental data obtained by ISVR in the frame of the European Project FLOCON. It is shown that the structure of the flow field near the trailing edge is strongly affected by the presence of the serrations. The integral scale lengths of the flow structures in the wake near the trailing edge, are much smaller than in the baseline case. The OASPL directivities of the acoustic far-field are in good agreement with the experimental data, and the serrated airfoil presents a reduction of acoustic PSD in the low and mid frequency ranges, with a reduction ranging from ∼ 10 dB at low frequencies, to ∼ 5 dB in the mid range. For higher frequencies, the PSD levels of the serrated airfoil become comparable (f ≈ 4000 Hz) and then are higher with respect to the baseline spectrum.

SUMMARY An efficient discontinuous Galerkin formulation is applied to the solution of the linearized Euler equations and the acoustic perturbation equations for the simulation of aeroacoustic propagation in two‐dimensional and axisymmetric problems, with triangular and quadrilateral elements. To improve computational efficiency, a new strategy of variable interpolation order is proposed in addition to a quadrature‐free approach and parallel implementation. Moreover, an accurate wall boundary condition is formulated on the basis of the solution of the Riemann problem for a reflective wall. Time discretization is based on a low dissipation formulation of a fourth‐order, low storage Runge–Kutta scheme. Along the far‐field boundaries a perfectly matched layer boundary condition is used. For the far‐field computations, the integral formulation of Ffowcs Williams and Hawkings is coupled with the near‐field solver. The efficiency and accuracy of the proposed variable order formulation is assessed for realistic geometries, namely sound propagation around a high‐lift airfoil and the Munt problem. Copyright © 2011 John Wiley & Sons, Ltd.