Identification and assessment of flow-induced sound sources inside encapsulated flow domains - Investigating a clinically applied hydraulic prosthesis

Noise emissions of hydraulic prostheses can have significant negative impacts on users and their environment. In this context, the sound production mechanisms inside the hydraulics of a clinically-applied knee prosthesis were investigated with the goal to identify tonal and broadband source regions and assess counter measures. Therefore, scale resolving incompressible and weakly compressible flow simulations are used to calculate acoustic sources based on common aero-acoustic formulations inside the encapsulated flow domain. These sources are visualized both in time and frequency domain to obtain qualitative information about their location and underlying source mechanisms. This analysis allows to distinguish between wall excitation based on turbulent incompressible flow phenomena on the one hand and compressible wave propagation effects on the other. Finally, validation experiments show a reduction of noise emissions obtained by adaptation of the flow guidance based on elimination of one source mechanism that is identified during the analysis.