Turbofan Engine Lubrication System Performance Calculation And Analysis

As we know, the Lubrication and Oil System (LOS) of aero-engines is one of indispensable systems which ensures their operation reliability and life-span, so it should be analyzed and investigated thoroughly. So the paper examined the performance characteristics of the LOS of a certain existent Turbo-Fan Aero-engine (TFAE) theoretically and experimentally, and considered how to improve it in order to suit the situations which the engine can work reliably used in Unpiloted Aerial Vehicle (UAV) at High Altitude and Long Endurance (HALE).The LOS of the TFAE includes a oil tank, a oil sump (four series gear sump, one series as oil supply sump, another three series as scavenge oil sump), oil filters, oil valves, oil jets and oil pipes and so on, and are divided into four basic subsystems—the press or supply oil process, scavenge oil process, cool oil process and breather process, and then how it work is described in detail. In the paper mathematical models are presented of the flux and press distribution of the oil flow and the thermal network analysis of the LOS based on the theories including the theory of aero-engine, hydrodynamics, heat transfer, thermodynamics engineering, and control theory & engineering. In the models, a method combined the test data with the analytical calculation is developed and applied. The data are obtained from the experiments carried out at a wide range of the altitude on the test-drive rig by simulating air flow, and the characteristic curves of main components and elements, such as oil supply pump, fuel-oil exchanger, the valve regulating the oil press are scored, so the experimentative coefficients are gotten. Also the models of four basic subsystems applied in the computation and analysis of stable-state are established utilizing the flow network theory and the thermal network analysis theory.A computer program based on mentioned models is offered in FORTRAN 90 & Visual C++, which is composed of a main program and several subprograms. In the main program, all the data of the LOS are input and recorded data output. The involved subprograms are the calculation of basic equations for the parts' performance and the expression of density and viscosity depending on the oil temperature. When calculation is carried out, a certain flow rate for each jet is forced to converge by iteration. If the iteration issuccessfully performed for the LOS, then all the calculated data are written on the output files.The results show that when the altitude is higher than 12km (the design altitude of the mentioned TFAE), the LOS does not work availably, because the lower atmosphere press in cavities and the higher shaft revolutionary of the oil pump lead to the lower intake oil press and a higher anti-press due to a stronger centrifugal effect. Otherwise, the common problems and the factors with an affect on the performance of the LOS encountered in the LOS analysis are discussed, as well as ways to deal with them.