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A Numerical Method for the Linearized Euler Equations Applied to Turbo-machinery NoisePropagation Through the Engine Exhaust
No full textA Discontinuous Galerkin Method for the Solution of the Linearized Navier-tokes Equations
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A Frequency-Domain Linearized Euler Model for Turbomachinery Noise Radiation Through Engine Exhaust
No full textA 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 dat
Numerical study of self-noise produced by an airfoil with trailing-edge serrations
No full textThe 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 × 105 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
Extraction of Proper Orthogonal Decomposition Modes for Optimal Aerodynamic Shape Design
No full textNumerical Prediction Method for Turbomachinery Noise Radiation Through the Engine Exhaust
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