Role of flow alignment and inlet blockage on vaned diffuser performance

Abstract

A computational investigation of the effects of inlet conditions on straight-channel diffuser performance is undertaken. The steady, three-dimensional, Navier-Stokes solver used for the investigation is found to adequately model the performance of a diffuser that has been previously examined experimentally. Results indicate that, contrary to the established view, vaned diffuser channel performance is weakly dependent on throat blockage. Rather, channel pressure rise is strongly affected by flow angle alignment with the diffuser centerline; misalignment of the flow can cause separation and reduced channel performance. This result challenges current design methods, and indicates that the designer is capable of sculpting the diffuser vanes to change the flow angle alignment, thus enabling control of both performance and range. In support of experimental results, overall diffuser performance is found to be largely independent of inlet axial distortion. Inlet nonuniformities are attenuated within the diffuser channel due to a spanwise work transfer which energizes regions of high flow angle misalignment, thus preventing the development of localized channel stall, and preserving good diffuser performance. This result indicates that axially twisted vanes, which are tailored for nonuniform inlet flow, may be unnecessary; simple untwisted vanes display no loss of performance when subjected to severe inlet distortion.