Frequency-Domain Linearized Euler Model for Turbomachinery Noise Radiation Through Engine Exhaust

摘要

A numerical model for the exhaust noise radiation problem is presented. In the model, it is assumed that annincoming wave is propagating through the exhaust nozzle, or the fan duct, and radiating outside. The near-fieldnpropagation is based on the solution of the linearized Euler equations in the frequency domain: for each wavennumber, a linearized Euler problem is solved using a finite element method on unstructured grids for arbitrarilynshaped axisymmetric geometries.The frequency-domain approach enables the suppression of theKelvin–Helmholtzninstability waves.Moreover, each single calculation, limited to a single frequency, is well suited to the exhaust noisenradiation probleminwhich the incomingwave can be treated as a superposition of elementary ductmodes.To reducenthe memory requirements, a continuous Galerkin formulation with linear triangular and quadrangular elements isnemployed and the global matrix inversion is performed with a direct solver based on a parallel memory distributednmultifrontal algorithm for sparse matrices. The acoustic near field is then radiated in the far field using thenformulation of FfowcsWilliams andHawkings. Numerical calculations for a validation test case, theMunt problem,nand two turbomachinery configurations are compared with analytical solutions and experimental data.