Research in Engineering and Aviation
Axial-gap eﬀects on the propagation of unsteady ﬂow in cascades
This paper investigates the effects of stator-to-rotor axial gap on the two-dimensional propagation of pressure disturbances due to potential-flow interaction and viscous-wake interaction from upstream blade rows in axial-turbine-blade rotor cascades. Results are obtained by modeling the effects of the upstream stator viscous wake and potential-flow field on the downstream rotor flow field and computing the unsteady flow fields in the rotor frame. The amplitudes of the two types of interaction for typical turbines are based on a review of available experimental and computational data. The potential-flow field is modeled as a sinusoidal pressure disturbance of amplitude 4% of the local pressure across the stator trailing edges that decays downstream. The velocity wake is modeled as a Gaussian velocity defect of varying amplitude and width, depending on the axial gap between the blade rows. The wake amplitudes and widths are based on conservation of loss of incoming momentum to the rotor due to the wake. The axial gap between rotor and stator is varied to show how the two interactions propagating in different directions reinforce or counteract each other at different axial gaps. The corresponding forces on rotor blades are computed for typical values of reduced frequency.