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research-article

EXPERIMENTAL INVESTIGATION OF TURBINE STAGE FLOW FIELD AND PERFORMANCE AT VARYING CAVITY PURGE RATES AND OPERATING SPEEDS

[+] Author and Article Information
Johan Dahlqvist

KTH Royal Institute of Technology, Stockholm, Sweden
jdahlq@kth.se

Jens Fridh

KTH Royal Institute of Technology, Stockholm, Sweden
jens@energy.kth.se

1Corresponding author.

ASME doi:10.1115/1.4038468 History: Received August 22, 2017; Revised October 26, 2017

Abstract

The aspect of hub cavity purge has been investigated in a high-pressure axial low-reaction turbine stage. A full-scale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely a high loading design case, and two high speed points encompassing the peak efficiency. At each of these operating speeds, the amount of purge flow was varied from 0% to 2%. The prominent effect due to purge is seen in the efficiency, showing a linear sensitivity to purge of 1.3%-points for every 1% of added purge flow for the investigated speeds. While spatial average values of flow angle and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible at higher span, with associated decreased turning. A radial efficiency distribution is utilized, showing negative impact through span heights from 15% to 70%. Pitchwise variation of investigated flow parameters is significantly influenced by purge flow, making this a parameter to include for instance when evaluating benefits of stator clocking positions.

Copyright (c) 2017 by ASME
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