Surface integration method used on semi-solid surface for fan noise prediction.

Abstract

As a continuation of previous work, the Ffowc-Williams and Hawkings model was applied to an axial fan that was operated under unfavorable inflow condition. A thin aluminum foam screen that is used as a treatment for disturbed inflow condition was included as a noise source in computational aeroacoustic simulation. The incompressible URANS model was used for the CFD simulation and the inflow foam was modeled as a homogeneous porous zone with permeability and inertial resistance factors found experimentally. Since the homogeneous porous zone defined in this way does not have a solid structure that could be used as a dipole noise source, the control surface integration method was applied to the surface of the homogeneous porous zone: i.e., to a surface right between the normal fluid zone and the porous zone. The unsteady pressure data on the control surface under the incompressible assumption was treated as representing pressure fluctuations on a semi-solid surface rather than as a representation of acoustic sources within the volume surrounded by the control surface.