Performance study and modelling of an integrated pump and gas-liquid separator system: Optimisation for aero-engine lubrication systems

It works efficiently and can be used in many applications (nuclear power plants,

pulp and paper processing, petroleum extraction, etc.). However, this pump and separator

system (PASS) was especially designed to handle air-oil mixture generated in

aero-engine lubrication systems. The PASS combines three important functions of the

scavenge part of the lubrication system: the deaeration and deoiling of the air-oil mixture

generated in the bearing and gearbox sumps and the pumping of the oil towards

the tank. These are critical functions for the engine. Indeed, a poor deoiling efficiency

leads to a high oil consumption. This reduces the flight endurance, increases the size

and weight of the oil tank and has a negative impact on the environment. Poor deaeration

and pumping characteristics lead to problems in the cooling and the lubrication of

the engine bearings.

Integrating a PASS into the lubrication system allows considerable improvements

(and simplification) to the lubrication system architecture. An important number of

components are suppressed: the vent lines, the deoiler, the cyclone deaerator and the

scavenge pumps. This reduces the size and the weight of the lubrication system and

increases its reliability. Furthermore, an important part of this PhD thesis focuses on

reducing the oil consumption in the PASS. This improves the flight endurance, reduces

engine maintenance and working costs and is profitable to the environment.

In addition to the development of an advanced PASS design system, the objective of

this thesis was to obtain a good understanding of the separation processes occurring in

the PASS and to develop theoretical models able to predict the separation performance

for every working condition encountered in a typical aircraft flight. To achieve this

goal, three main tasks were performed: the development of different two-phase measurement

systems, the experimental tests of four different PASS architectures and the

theoretical development (after an extensive literature review) of correlations predicting

the performance of the PASS in function of the working conditions. Five specific aspects

of the PASS were studied: the inlet flow, the deoiling efficiency, the deaeration efficiency,

the pumping efficiency and the pressure drop. Finally, the models that have been developed

with the help of the measurement systems and of the experiments have been

integrated in a complete model of the lubrication system (under the EcosimPro modelling

environment). This helps to predict real in flight PASS working conditions and

performance. Indeed, the PASS is very sensitive to the engine working conditions and

an optimisation of the prototype size and performance is only feasible with an accurate

knowledge of these working conditions and a complete lubrication system model.

Finally, with the results of this PhD thesis, a new PASS design, optimised for different

aero-engine lubrication systems, is presented.