The Unsteady Forces Due to Viscous Wakes in Turbomachines

Tonal and Broadband Noise Control of an Axial Flow Fan with Metal Foams: Design and Experimental Validation

“…The first is the potential interaction, which causes pressure fluctuations on both the upstream and downstream blades surfaces. Some investigators have suggested that the potential interaction dominates only when the separation of the adjacent cascade rows is less than 50% of the blade chord [27,28]. For the axial-flow fan studied in this work, the chords of the UMPs and OGVs are very long, so we believe that the potential interaction is a possible reason generating pressure fluctuations on blade surfaces.…”

Unsteady flows in a single-stage transonic axial-flow fan stator row

“…Interactions was published In 1953 by Kemp and Sears [50,51] who studied the aerodynamic Interference between rotor and stater blade rows for Lefcort considered that the unsteady forces In turbomachlnes were due to four main effects: a circulation effect, a blade thickness effect, a wake effect, and a wake distortion effect. The above mentioned blade-row…”

Lifting Fan Noise Studies

“…Thus, if the Fourier coefficients of the loading harmonics are established, the fluctuating lift can be calculated by the methods established by Kemp and Sears (7,8). While some study of the wake profiles shed by the rotor blades is proposed to be undertaken in the near future, in the meantime the discrete frequency noise level will be discussed qualitatively in the light of the foregoing theory.…”

“…Fig.4 shows the existence of discrete tone up to four harmonics confirming the theoretical suggestion. Kemp and Sears (7,8) showed that the fltqctuating force on the blade depends upon two effects; the potential flow interaction between the blades and the effect of viscous wakes from an upstream blade row impinging on a downstream blade row. The velocity field due to the potential flow interactions is proportional to the inverse square of the distance, while the velocity decrement in a wake is approximately proportional to the inverse of the distance.…”