Aero-Acoustical Design of Unevenly-Pitched and Multi-Curvature-Bladed Fans of Automobile Cooling-Pack System

초록

We applied a BEM (Boundary Element Method) to capture the frequency characteristics from rotating blades, which is a highly efficient method in the sense of economic computation. However, boundary integration is not easy for the complex and moving surface such as a rotating blade. Thus, a fictitious Kirchhoff surface is designed in an effort to overcome the difficulty resulting from complex boundary conditions. Acoustic sources may be distributed on each Kirchhoff surface element depending on their acoustic characteristics. In this research, the shroud fan in an automobile cooling-pack system is assumed to have unsteady loading noise as a dominant source. Dipole sources for the FW-H equation were computed based on LES of 2D sectional airfoil from the impeller’s hub to tip. Acoustics fields were then computed by using the optimum shape and location for Kirchhoff Surface. The uneven, 5-bladed fan resulted in 6 dB(A) reduction at the first BPF and a significant reduction in an overall SPL, compared with the regular fan of same performance at the same operating point. The blade surface having many curvatures was introduced to improve the sound quality by modulating the 3D flow structures over and around the airfoil, and their noise characteristics are discussed by using the fore-mentioned technique.