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research-article

SECONDARY FLOW CONTROL IN LOW ASPECT RATIO VANES USING SPLITTERS

[+] Author and Article Information
Christopher J. Clark

Whittle Laboratory, University of Cambridge, 1 JJ Thomson Avenue, Cambridge CB3 0DY, UK
cjc95@cam.ac.uk

Graham Pullan

Whittle Laboratory, University of Cambridge, 1 JJ Thomson Avenue, Cambridge CB3 0DY, UK
gp10006@cam.ac.uk

Eric M. Curtis

Whittle Laboratory, University of Cambridge, 1 JJ Thomson Avenue, Cambridge CB3 0DY, UK
emc1000@eng.cam.ac.uk

Frederic Goenaga

Rolls Royce. Bristol BS34 7QE, UK
Frederic.Goenaga@rolls-royce.com

1Corresponding author.

ASME doi:10.1115/1.4036190 History: Received December 02, 2016; Revised January 11, 2017

Abstract

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary ?ows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary ?ow strength and improves stage performance. The total secondary kinetic energy of the secondary ?ow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter con?guration, 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 splitters 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 ?ow?eld 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 ef?ciency increased by 0.88%.

Rolls-Royce plc
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