Rig tests and computational fluid dynamic (CFD) modelling have been used to improve the understanding of the effect% of component geometry and air bleed flows on the pressure and velocity variations in the rotor-stator cavity found typically behind the impeller of a gas turbine engine centrifugal compressor.Ranges of axial gap ratio and bleed throughflow typical of those found in current gas turbine engine design have been investigated with close attention to radial inflow (centripetal) bleeds with and without initial swirl.CFD models have been constructed corresponding to the test conditions to assist in the understanding of the test data and to validate the computational methods. These methods can be used to extend the ranges of geometry, rotational Reynolds number and throughflows studied with greater confidence, thereby providing a design tool for direct use in the gas turbine industry.

Research has been conducted into the effects of component geometry and air bleed flow on the radial variation of static pressure and core tangential velocity in a rotor-stator cavity of the type often found behind the impeller of a gas turbine engine centrifugal compressor. A CFD code, validated by rig test data for a wide range of rotor-stator axial gaps and throughflows, has been used to generate pressure and velocity data for typical gas turbine operating conditions. This data has been arranged as a series of simple design curves which relate the rotational speed of the core of fluid between rotor and stator boundary layers, and hence the static pressure distribution, to primary cavity geometry, rotational Reynolds number and bleed throughflow with particular attention to radial inflowing bleeds. Details are provided on the use and limitations of these curves. Predictions using this method have been compared successfully with measured data from engine test and a compressor test rig, modified to facilitate variable quantity and direction of impeller rear face bleed flow, at typical gas turbine operational power conditions. Data generated by these curves can be used directly in the design process and to validate integral momentum methods which can provide relatively simple computation of rotor-stator cavity pressure and velocity distributions independently or within air system network programs. This approach is considered to be a cost and time effective addition to the analytical design process especially if validated CFD code, which can accommodate rotational flows consistently and accurately, is not available.

The specific thrust and fuel efficiency of gas turbine engines have improved considerably over the last 20 years primarily due to technology advances in materials science and main gas path thermo-fluid analysis. However, a major influence on the improved engine reliability demonstrated over that same timeframe is the performance of engine mechanical systems which rely on the consistent delivery and recovery of oil. The general architecture of oil systems has changed little over this period. However, detailed attention to how oil system components behave and interact with each other, and with the rest of the engine systems, has helped achieve improved engine mechanical performance. For derivative engines this process is facilitated by a substantial amount of in-service data, reflecting both good and bad experiences, which helps to identify the poor designs, manufacturing anomalies or unusual operational circumstances that are likely to cause problems and the design changes that are needed to solve them. However, new engines being designed and certificated in ever-reducing timescales, do not necessarily have the luxury of such directly relevant, in-service, performance data. Hence it is essential that oil systems are designed with a full appreciation of component and system capabilities and the options available. This knowledge is based fundamentally on a general awareness of how an engine oil system achieves its objectives, why sometimes it doesn’t, and how it integrates with the rest of the engine. This paper aims to identify some of the decisions that need to be made regarding system architecture and component sizing when designing a gas turbine oil system. Full attention to these matters during the engine design phase should lead to reduced development and in-service problems, less use of development innovation to solve problems and ultimately improved engine reliability.

The flow in the secondary air system of a gas turbine engine passes over numerous oil supply and scavenge pipes and a fracture in such a pipe will cause a jet of oil to be ejected as a spray. This spray will disperse in the surrounding flow. Accurate and reliable numerical modelling of these sprays presents significant problems due in part to their complexity, but also the lack of experimental data available for model validation. This paper describes the design, manufacture, testing and results from an experimental test rig aimed at spray characterisation. The sprays considered were produced through a round sharp edged nozzle with a 0.57 mm diameter and a length to diameter ratio of 1.61. The spray was introduced normal to the cross flow. Phase Doppler Anemometry was used to determine droplet size and velocity for Weber numbers within the range of 13 < Weg < 580 and Momentum Flux Ratio within the range of 0.8 < q < 136, resulting in 19 different spray fields. Each of these spray fields has been characterised at three axial locations. Contours of droplet size, mass flux distribution, axial droplet velocity and transverse droplet velocity are presented. In addition, a pulsed laser sheet and CCD camera were used to analyse the jet behaviour in terms of break up length and jet trajectory.