Fundamentals of Aeroacustics

Course Objective

Students acquire fundamental knowledge about sound generated aerodynamically and about sound propagation in moving media. Students know the basic terms and analytical computation methods of classical acoustics. Students know about the combination of the basic terms of acoustics and aerodynamics to aeroacoustics as an interdisciplinary topic in engineering science. Students know the basic mechanisms of aerodynamic sound generation and can explain the various phenomena related to sound propagation. Students are able to reduce applied problems in the field of aeroacoustics to the relevant equations and can identify source mechanisms. Students are able to orient themselves independently in literature on aeroacoustics.

Course Content

• basic terms of acoustics, acoustic wave equation for non-moving medium / fundamental solutions in 1D/2D/3D, notion of source, general solution to wave equation through Greens functions, multipole expansion of sources
• surface interaction: impedance/admittance, Kirchhoff-integral for extrapolation of sound field quantities to farfield, convective wave equation:
• sources and propagation in uniformly moving media, convective amplification, Doppler shift, cut-on/cut-off condition in duct flows
• analytical description of sound propagation in sheared media, refraction at temperature layers and shear layers, zone of silence, total reflection
• moving sources of sound, Lighthills equation, aeroacoustic source mechanisms,
• Ffowcs-Williams Hawkings equation, sound of flow past
• simple lecture hall experiments: propeller subject to non-uniform inflow, edge noise, sound examples from loudspeaker