The Control of Shroud Leakage Flows to Reduce Aerodynamic Losses in a Low Aspect Ratio, Shrouded Axial Flow Turbine

Author:

Wallis A. M.1,Denton J. D.2,Demargne A. A. J.2

Affiliation:

1. Siemens Power Generation U.K. Ltd., Newcastle upon Tyne, United Kingdom

2. Cambridge University, Cambridge, United Kingdom

Abstract

The losses generated by fluid leaking across the shrouds of turbine blade rows are known to form a significant proportion of the overall loss generated in low aspect ratio turbines. The use of shrouds to encase the tips of turbine blades has encouraged the development of many innovative sealing arrangements, all of which are intended to reduce the quantity of fluid (the leakage fraction) leaking across the shroud. Modern sealing arrangements have reduced leakage fractions considerably, meaning that further improvements can only be obtained by controlling the leakage flow in such a way so as to minimise the aerodynamic losses incurred by the extraction and re-injection of the leakage flow into the mainstream. There are few published experimental investigations on the interaction between mainstream and leakage flows to provide guidance on the best means of managing the leakage flows to do this. This paper describes the development and testing of a strategy to turn the fluid leaking over shrouded turbine rotor blade rows with the aim of reducing the aerodynamic losses associated with its re-injection into the mainstream flow. The intent was to extract work from the leakage flow in the process. A four stage research turbine was used to test in detail the sealing design resulting from this strategy. A reduction in brake efficiency of 3.5% was measured. Further investigation suggested that much of the increase in loss could be attributed to the presence of axial gaps upstream and downstream of the shroud cavity which facilitated the periodic ingress and egress of mainstream fluid into the shroud cavity under the influence of the rotor potential field. This process was exacerbated by reductions in the leakage fraction.

Publisher

American Society of Mechanical Engineers

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1. Numerical Simulation of Leakage Flow Inside Shroud and Its Interaction with Main Flow in an Axial Turbine;Liutex and Third Generation of Vortex Definition and Identification;2021

2. Effects of Double-Side Labyrinth Seals on Aerodynamic Performance in a Transonic Shrouded Turbine Stage;Journal of Engineering for Gas Turbines and Power;2020-01-13

3. Features of the Vortex Flow Structure around a One Fin Shroud;Thermal Engineering;2019-06-24

4. Numerical Investigation of the Interaction between Mainstream and Tip Shroud Leakage Flow in a 2-Stage Low Pressure Turbine;Journal of Thermal Science;2014-05-13

5. Introduction;Unsteady Computational Fluid Dynamics in Aeronautics;2014

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