Experimental investigation of turbine stator well rim seal, reingestion and interstage seal flows using gas concentration techniques and displacement measurements

Gas turbine engine performance requires effective and reliable internal cooling over the duty cycle of the engine. Life predictions for rotating components subject to the main gas path temperatures are vital. This demands increased precision in the specification of the internal air system flows which provide turbine stator well cooling and sealing. This in turn requires detailed knowledge of the flow rates through rim seals and interstage labyrinth seals. Knowledge of seal movement and clearances at operating temperatures is of great importance when prescribing these flows. A test facility has been developed at the University of Sussex, incorporating a two stage turbine rated at 400 kW with an individual stage pressure ratio of 1.7:1. The mechanical design of the test facility allows internal cooling geometry to be rapidly re-configured, while cooling flow rates of between 0.71 CW, ENT and 1.46 C W, ENT, may be set to allow ingress or egress dominated cavity flows. The main annulus and cavity conditions correspond to in cavity rotational Reynolds numbers of 1.71×106< Reφ <1.93×106. Displacement sensors have been used to establish hot running seal clearances over a range of stator well flow conditions, allowing realistic flow rates to be calculated. Additionally, gas seeding techniques have been developed, where stator well and main annulus flow interactions are evaluated by measuring changes in gas concentration. Experiments have been performed which allow rim seal and re-ingestion flows to be quantified. It will be shown that this work develops the measurement of stator well cooling flows and provides data suitable for the validation of improved thermo-mechanical and CFD codes, beneficial to the engine design process. Copyright © 2011 by Rolls-Royce plc.

Lift and the leading edge vortex

Leading edge vortices are considered to be important in generating the high lift coefficients observed in insect flight and may therefore be relevant to micro-air vehicles. A potential flow model of an impulsively started flat plate, featuring a leading edge vortex (LEV) and a trailing edge vortex (TEV) is fitted to experimental data in order to provide insight into the mechanisms that influence the convection of the LEV and to study how the LEV contributes to lift. The potential flow model fits the experimental data best with no bound circulation, which is in accordance with Kelvin's circulation theorem. The lift-to-drag ratio is well approximated by the function 'cot α' for α > 15°, which supports the tentative conclusion that shortly after an impulsive start, at post-stall angles of attack, lift is caused non-circulatory forces and by the action of the LEV as opposed to bound circulation. Copyright © 2012 by C. W. Pitt Ford.