An experimental study of windage due to rotating and static bolts in an enclosed rotor-stator system

摘要

The cooling air in a gas turbine engine is subject to windage as it flows through the internaludair system. The work in this thesis focuses on the windage generated as the cooling airudpasses over the rotor surface, particularly for case where bolts are encountered. Reducingudwindage heating of the cooling air is of great importance to turbomachinery engineers,udparticularly in the aerospace industry, since the use of compressor air for cooling greatlyudreduces the thrust potential of an engine. The ability to accurately predict windage can helpudreduce the quantity of cooling air required, resulting in increased efficiency.ududA purpose built rig was used to measure both windage and rotor surface temperature as airudpasses through an enclosed rotor-stator cavity. A wide range of flow conditions were testedudwith some being close to those found in a modern gas turbine engine. A variety of bothudstator and rotor mounted bolts were investigated, of varying size and shape, as well asudcavities in the disc surface. In addition, PIV measurements of the core tangential velocityudwere obtained.ududTest results show that windage is increased substantially with rotor bolts present, compared with a plain disc, and that it increases with increasing bolt size. For hexagonal rotor bolts a new correlation was produced between the moment coefficient and bolt diameter to pitch ratio for a range of flow conditions, characterised by the rotational and throughflow Reynolds numbers. Stator bolts were shown to generate a large increase in disc surface temperature compared with the plain disc at engine representative conditions.ududPIV measurements of the core tangential velocity showed an increase of up to 80% aboveudthe plain disc with rotor bolts present and no superimposed flow. When throughflow wasudintroduced, the increase was around 300%. These measurements also demonstrate a localudincrease in tangential velocity in the region close to the bolt.