Авіаційно-космічна техніка та технологія (Dec 2018)
AN ASSESSMENT OF FOUR STAGE AXIAL POWER TURBINE DISKS’ AIR-COOLING SYSTEM BASED ON THERMAL-HYDRAULIC MODELING
Abstract
A hydraulic analysis of four stage axial power turbine cooling system was performed. A practical application of the existing algorithms of thermal-hydraulic analysis is considered. Reasonable flow-rate distribution among the cooling channels and cooling system air leakage waste reduction are discussed. An implementation of the rotor screen dividing rotor internal cavity into disk and shaft cavities is revealed as the best way to keep the flow-rate balance of cooling air in account of achievement simplicity. This paper also covers a key design concept that the structure of turbine shall be such as to promote good dissipation of heat from blades to disks by means of air flow passing through special channels between rotor parts. A turbine disks’ air-cooling system assessment importance is shown according to the aim of hot gas ingress prevention. It is given a brief description of known theoretical fundamentals on which the used thermal-hydraulic analysis computational method of modeling was based. Flow-rate distribution among the four stage axial power turbine disks’ air-cooling system is noted to be carried out by certain basic design choices such as labyrinth seals, fins and ledges. The most important factors on which the flow-rate distribution depends on are mentioned including a ratio of narrow section hydraulic area to channel section hydraulic area, hydraulic resistance and availability of centrifugal pressure between disks. Narrowing of cooling flow passage section causes air velocity increase and pressure reduction. Even though some recovery of velocity appears downstream the narrowing element, the pressure value changes its magnitude due to vortex losses. Therefore it makes possible to provide the required air distribution. The considered rotor screen structure confirmed its functionality in operating gas turbine plant and it is stated as achieved results. Numeral details of dealt analysis are omitted. Generally, the behavior of flow and heat exchange in area between rotating disks is classified as rather complicated and methods of its modeling are summarized to remain relevant question of further studies.
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