Department of Mechanical Engineering

Endwall contouring in gas turbines project

An experimental and CFD study to improve gas turbine efficiency through optimised rim seals and end-wall contours design with both main and purge flows present.

Modelling upstream wheel-space, rim seals and mainstream gas path

Designers of modern gas turbines use End-Wall Contouring (EWC) to influence the static pressure field between vanes and rotating blades; an improvement in aerodynamic performance can be achieved by guiding the secondary end-wall flow and reducing the associated losses.

This secondary flow-field is significantly influenced by the egress of purge flow through rim-seals at the hub end-wall and the ingress of hot gas is itself influenced by the EWC.

The interaction between the egress and mainstream, and its propagation through the downstream rotor, is complex and unsteady. Industry is moving towards a combined design of the rim-seal geometry, seal-clearance profile and mainstream end-wall contours, principally through the use of computational fluid dynamics (CFD).

This project is focused on the design and build of a rotating-disc rig to experimentally model the upstream wheel-space, rim seals and mainstream gas path of the first stage of a gas turbine.

The test facility is being specifically designed for optical access and will feature interchangeable EWC profiles and rim-seal geometries on the stator and rotor.

Innovative experimental techniques

The following measurements will be made above the rim seal and through the blade passage in the annulus: ‘Carbon Dioxide Planar Laser-Induced Fluorescence’ (CO2-PLIF); and ‘Three-component Volumetric Velocimetry’ (V3V). The CO2-PLIF measurements will allow the trajectory of rim-seal egress and its interaction with the main-annulus flow to be visualised.

cad-model-endwall-contouringThe V3V measurements will provide three-component velocities through the blade passage, enabling secondary-flow structures to be observed. This use of both of these techniques in gas turbine experiments will be world firsts; the data and insight provided by these applications will provide unprecedented data for engine designers for validation of their CFD models.

The rig will also be used to make the following measurements in the rotor-stator wheelspace cavity: the distribution of pressure and concentration with radius on the stator disc; and the variation of sealing effectiveness over a range of purge flow rates.

These pressure and concentration measurements—combined with the aforementioned CO2-PLIF and V3V measurements—will provide information that addresses the impact of the rim-seal and EWC designs on the purge-mainstream flow interaction and the resulting effects on ingress to the wheel-space and on the formation of aerodynamically parasitic secondary flow structures in the blade passage.

The measurements will feed into a CFD phase of this project for design of rim-seal and EWC geometries that are optimised for both reduction in ingress into the wheelspace and maximisation of the efficiency of the turbine stage through reduction in secondary flow losses. An efficiency improvement of 1.4% is predicted.