Methods of Aeroacoustics

Course Objective

Students know the essential analytical, numerical and experimental methods for the solution of aeroacoustic problems in the engineering practice. Students are aware of the strengths and weaknesses of the various methods of analysis in aeroacoustics; they can select in a targeted way the appropriate method and can assess obtained results in a critical way.
Students have insight into the parametric dependencies of different aerodynamically caused tonal and broadband sources of sound. The students are informed about methods insofar as they may apply or develop respective procedures for prediction or measurements.
The excursion conveys the practical use of experimental measurement methods for sound generated aerodynamically to the students. The contents put the students in the position to further elaborate on the experimental methods presented in the lecture and to recognize the meaning of the aeroacoustic experiment as the basis for the validation of computational methods.

Course Content

Analytical methods:

• Prediction of tonal propeller sound on the basis of the Ffwocs-Williams and Hawkings equation
• Prediction of turbulence related edge noise by reciprocity theorem or method of matched asymptotic expansion.

Numerical methods:

• Acoustic boundary element method, ray-tracing, highly resolving finite difference methods for the solution of the linearized Euler equations, dispersion- and dissipation error.
• Application of perturbation methods for aeroacoustic problems

Experimental methods for the measurement and localization of sound:

• Characteristics of microphone types, microphone
• Corrections, measurement of sound in flows, sound localization with elliptic mirror or microphone array. Transfer of source data from wind tunnel experiments to flyover- or drive-by situations.
• Aeroacoustic wind tunnel correction