Verification of noise prediction through acoustic analogy

This paper makes a contribution to the definition and evaluation of verification test cases for a far-field noise formulation in the time domain, in which the 3D Ffocws Williams and Hawkings equation is used to predict the noise level from bodies in arbitrary motion. The focus will be on the definition and verification of test cases for quadrupole noise contribution and dipole noise from shear stress sources. For verification purposes, the radiation of a multi-polar structure of aero-acoustic sources in a subsonic flow, described by Bailly for the two-dimensional linearized Euler equations, is chosen as a test case. The acoustic pressure signature, sound pressure level and directivity are computed for each test case. An excellent agreement between the 3D numerical approach and the 2D analytical solution is observed. The paper goes on to present a conformation of the formulation Q1A of Brentner, which includes surface integrals for quadrupole noise prediction. It is shown that Q1A predicts quadrupole noise accurately for observers placed in the rotor frame, whereas an overpredicted noise is obtained for other observer positions.