The specific aspects of thermal and hydraulic processes in the oil cooler of an aviation gas turbine engine

Abstract

The modern gas turbine engines (GTEs) development is associated with an increase in the compressor pressure ratio and the gas temperature at the turbine inlet with a simultaneous reduction in the size and weight of the engine. The reliable operation of the GTE largely depends on the oil system excellence. In circulating oil systems, to ensure the lubrication and cooling of engine friction units, a high multiplicity of oil circulation is necessary. The preparation of oil for the next lubrication cycle is related to its cooling, cleaning of mechanical impurities formed during operation, and air separation. Oil coolers are used to cool the oil in GTEs. Air or fuel can be used as the cooling medium. Regardless of the cooling medium choice, a two-phase mixture (oil-air) and not a single-phase oil, as is considered when designing oil coolers, affects the course of thermo-hydraulic processes. Therefore, the subject of this paper is thermohydraulic processes in two-phase media. The goal of this study is to determine the specific aspects of thermohydraulic processes during the oil-air mixture cooling in an aviation gas turbine engine to further improve oil cooler design approaches. This paper aims to show the differences in the course of thermohydraulic processes in two-phase media from single-phase media and to emphasize the importance of considering them when designing oil coolers. The main results are as follows. For a two-phase flow, changes in temperature and pressure change not only the thermophysical properties of the phases but also the gas content, density, and speed of the mixture, which affects the course of thermohydraulic processes in the oil cooler. Under certain combinations of parameters, the structure of the two-phase flow may change. A low value of the equilibrium speed of sound can lead to unpredictable operation of the oil cooler and the oil system as a whole. In addition, the presence of an oil-air mixture reduces the heat transfer capacity of the oil cooler compared with the results of calculations using standard methods. In conclusion, it can be stated that to increase the efficiency of the oil system, it is extremely important to establish the regularities of thermo-hydraulic processes for the two-phase flow of the oil-air mixture and consider this during the design of oil coolers.

Keywords

• маслорадіатор
• газотурбінний двигун
• двофазний потік
• теплогідравлічні процеси