A method is given for calculating the incompressible flow of a perfect fluid through multiple cascades of blades with one or more cascades moving relative to the frame of reference. Finite differences are used and the stream function evaluated by relaxation. From this velocities and pressures are calculated throughout the field for a sequence of relative blade positions allowing the spatial and time variations to be obtained. The method is applied to an i.g.v.-rotor combination with three values of axial spacing. The results show that the mechanism of blade row interaction is that the i.g.v. prevents accelerations of the fluid in the direction normal to the i.g.v. camber line which would occur if the i.g.v. were not present. The resultant pressure differences across the i.g.v. are the primary source of alternating forces and provide sources of discrete frequency noise at typical blade row axial spacings. The present investigation is confined to the near field and estimation of noise radiation is beyond its scope; however, if the analysis is used to design blades producing the minimum fluctuating pressures, relatively low noise radiation should result.
Discrete Frequency Noise Due to Irregularity of Blade Row of Axial Fan Rotor