Numerical investigation of tonal noise sources from centrifugal fan
Recirculating flows, which are responsible for reducing the fan efficiency and increasing the noise generation, are observed between the shroud and the blade trailing edges. It is found that the recirculating flows are associated with the gap between the shroud and the inlet duct.
The recirculating flow causes large modeled turbulence kinetic energy (TKE). The TKE is unevenly distributed among the blades due to the unsteady recirculating flow. Moreover, the position of the largest TKE periodically varies among the blades. The period corresponds to approximately 4 times the fan rotation period, it was also found in acoustic measurements.
Different pressure distributions among the blades are found and ascribed to the turbulence initializing from the inlet gap. The turbulence develops along the shroud wall and interacts with the blades at their leading edges. The interaction renders uneven surface pressure distributions among the blades as well as significant peak differences. As the distances to the inlet gap and the shroud increases, the difference of the pressure distributions among the blades decays. The wall-pressure fluctuations indicates that the locations of the tonal noise sources agree with the locations of the uneven surface pressure distributions and the significant pressure peaks, which are near the blade leading edges.
Blade Passing Frequency
Chalmers, Mekanik och maritima vetenskaper, Strömningslära
Martin Ottersten, Hau-Dong Yao and Lars Davidson - Numerical and experimental study of tonal noise sources at the outlet of an isolated centrifugal fan
Rymd- och flygteknik
Strömningsmekanik och akustik
Chalmers maritima simulatorer
Opponent: Prof. Mats Åbom, Department of Aeronautical and Vehicle Engineering, KTH Royal Institute of Technology, Sweden