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research-article

THE ROLE OF VORTEX SHEDDING IN THE TRAILING EDGE LOSS OF TRANSONIC TURBINE BLADES

[+] Author and Article Information
Andrew Philip Melzer

Whittle Laboratory, University of Cambridge, 1 JJ Thomson Avenue, Cambridge, CB3 0DY, UK
apmelzer@gmail.com

Graham Pullan

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

1Corresponding author.

ASME doi:10.1115/1.4041307 History: Received July 11, 2018; Revised August 23, 2018

Abstract

The loss of Square, Round, and Elliptical turbine trailing edge geometries, and the mechanisms responsible, is assessed using a two-part experimental program. In the first part, a single blade experiment, in a channel with contoured walls, allowed rapid testing of a range of trailing edge sizes and shapes. In the second part, turbine blade cascades with a sub-set of sizes of the trailing edge geometries tested in part one were evaluated in a closed-loop variable density facility, at exit Mach numbers from 0.40 to 0.97, and exit Reynolds numbers from 1.5 x105 to 2.5 x106. Throughout the test campaign, detailed instantaneous Schlieren images of the trailing edge flows have been obtained to identify the underlying unsteady mechanisms in the base region. The experiments reveal the importance of suppressing transonic vortex shedding, and quantify the influence of this mechanism on loss. The state and thickness of the blade boundary layers immediately upstream of the trailing edge are of critical importance in determining the onset of transonic vortex shedding. Elliptical trailing edge geometries have also been found to be effective at suppressing transonic vortex shedding. For trailing edges that exhibit transonic vortex shedding, a mechanism is identified whereby reflected shed shockwaves encourage or discourage vortex shedding depending on the phase with which the shocks return to the trailing edge, capable of modifying the loss generated.

Copyright (c) 2018 by ASME
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