Some challenges in turbomachinery for propulsion

Authors

M. Åbom - KTH-The Royal Inst. of Technology, Competence Centre for Gas Exchange (CCGEx)

Abstract

Turbomachines are rotating machines with impellers that are exchanging work with a fluid and during this process also produce sound. Due to the periodic nature of the operation this sound contains rotational harmonics but also broad band noise related for instance to unsteady inflow disturbances. In this paper a review of the subject is presented covering both experimental and numerical methods for acoustic characterization of turbomachines. A general problem in both cases being that simply using sound power to characterize a machine is not a solution, especially for smaller machines or low frequencies where the acoustic wavelength is of the order of the system size (diameter). For such case the source and system is coupled and more complex models are required. Special attention will be given to turbo-charge units for automotive applications, where presently there is a strong drive to deepen the understanding and develop better methods.