CUED Publications database

Secondary flow control in low aspect ratio vanes using splitters

Clark, CJ and Pullan, G and Curtis, E and Goenaga, F (2017) Secondary flow control in low aspect ratio vanes using splitters. Journal of Turbomachinery, 139. ISSN 0889-504X

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© 2017 by Rolls-Royce plc. Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high end-wall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy (SKE) of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet end-wall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not "jump" in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent current practice for a low aspect ratio vane, a design exempt from thickness constraints, and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitter geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flow field was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

Item Type: Article
Divisions: Div A > Turbomachinery
Depositing User: Cron Job
Date Deposited: 17 Jul 2017 19:26
Last Modified: 19 Jul 2018 07:05