IMPACT OF THE PRE-SWIRL NOZZLE LOCATION ON THE AIR TRANSFER SYSTEM (ATS) CHARACTERISTIC

In most industrial turbines the cooling air for rotating turbine blades is extracted from the compressor and transferred via passageways in the stationary parts and the rotor to the blade roots. These passages form the stator-rotor air transfer system (ATS). In stationary part of the ATS the air is usually pre-swirled in the direction of rotation to reduce the temperature and to minimize the losses in the transition area. This paper presents the investigations of the impact of the pre-swirl nozzle location on the ATS characteristics. Two ATSs have been compared. Both have a similar design, with the main difference related to the position of a pre-swirl nozzle. In the first system the pre-swirl nozzle is located at the inlet, and in the second it is located at the outlet of the stationary part of the ATS. The detailed flow structure and characteristics of both systems have been calculated using commercial CFD code. The 3-D calculations provide better insight into the dominant physical mechanisms in complex, rotating, turbulent flow and allow the calculation of the performance of these systems under various conditions. The CFD calculations have been used for the calibration of the cooling system hydraulic model, and the latter was compared with the available measured data. The study showed that the two ATSs considered have very similar characteristics (i.e. similar reduction of cooling air temperature and similar losses) despite the fact that the flow structure is significantly different. Therefore, this design can be considered as neutral to the pre-swirl nozzle location, and this is a positive feature ensuring flexibility of the system.