The aerodynamic loss due to tip leakage vortex of rotor blades represents a significant part of viscous losses in axial flow turbines. The mixing of leakage flow with the main rotor passage flow causes losses and reduces turbine stage efficiency. Many measures have been proposed to reduce the loss in the tip clearance area. In this paper the reduction of the tip clearance loss due to changes made to the blade tip section profile is presented. The blade tip profile was modified to decrease the pressure gradient between pressure surface and suction surface. This approach allows the reduction of tip leakage and tip vortex strength and consequently the reduction of tip clearance losses. A 3D Navier-Stokes solver with q-ω turbulence model is used to analyze the flow in the turbine with various tip section profiles. Test data of three single-stage experimental turbines have been used to validate analytical predictions: • Highly loaded turbine stage with a pressure ratio π0T = 3.2 and reaction degree ρmean = 0.5. • Two turbines with a pressure ratio π0T = 3.9. (One with high degree of reaction ρmean = 0.55; the other with low degree of reaction ρmean = 0.26). The numerical investigation of the influence of various tip section profiles on stage efficiency was carried out in the range of relative tip clearance 0.5%–2.4% with the objective of a decreasing the influence of the tip clearance on the stage efficiency.

The aero-redesign of a 50 Hz Gas Turbine GT13D3A is presented. The modifications enabling performance improvements are described, and the aero-design process is briefly discussed as well. The aerodynamic characteristics of an upgraded turbine (GT13DM) are compared with the original design (GT13D3A) and with the measurements in the field. The measurements confirmed the expected performance improvement.

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.

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