by S. Schoder: firstname.lastname@example.org , A. Wurzinger, C. Freidhager, M. Kaltenbacher, IGTE, TU Graz
Future power units of cars (the electric motor, battery, fuel cell) generate little noise during operation. Consequently, the noise of auxiliary units (cooling fan of a battery unit, the turbocharger of fuel cells  becomes an essential task of the developing process. Since performing robust measurements are costly and time-consuming, the presented validated simulation workflow enhances development and research .
Within this finished research project, we investigated the individual steps of the hybrid aeroacoustic workflow in detail. Based on existing benchmark data for low-pressure axial fans , the perturbed convective wave equation (PCWE) and the Ffowcs Williams and Hawkings analogy Farassat’s 1A (FWH) are analyzed. We performed a mesh convergence study and altered the turbulence modeling approach (visualization see Fig. 1).
Fig. 1: Q-criterion at instantaneous time, which is showing the turbulent structures of the tip flow.
The detached eddy simulation model and a grid of 23.4million cells delivered the most accurate sound radiation (see Fig. 2). The validation of the results allows us to conclude that the fluctuating flow pressure is the relevant flow-convergence criteria, motivated by the fact that it is the dominant source term both for PCWE and FWH.
Fig. 2: Sound propagation visualization.
Furthermore, we showed the robustness of the developed grid interpolation techniques  using the Richardson extrapolation. Considering the short duct, we found that for frequencies below 700Hz, FWH and PCWE deliver a comparable accuracy of sound prediction . However, for sources at a higher frequency, the directivity of the propagation matters (which the PCWE accounts for). Since most industrial applications have complicated geometries, including in-duct systems, the PCWE (discretized by the finite element method) is preferable.