Many Alstom heavy-duty gas turbines with a silo combustor are in service and moreover undergoing upgrades for performance augmentation, lifetime extension, and emission reduction. Several structural parts of the combustor are exposed to high gas temperatures, and therefore their lifetime depends mainly on the metal temperatures, which must be kept within the acceptable limits. This paper describes methodology based on the state of the art methods of 3D CFD and finite element (FE) computations, which are combined into the computational process for the reliable silo combustor thermal analyses. In the first part of the paper the computational model of the silo combustor is discussed. The model comprises CFD models simulating the hot gas path and the cooling air supply system, as well as the FE model of the structural parts. The CFD models predict the gas temperatures and heat transfer coefficients that are used by the FE model for calculating the metal temperatures. In the second part of the paper the computational results are presented and several 3D flow phenomena are analysed in details. One effect is the interaction of dilution jets in swirled cross flow. At different operation conditions, pairing of those jets occurs, which generates the periodic metal temperature distribution, as recorded in the field. This analysis also revealed factors, which influence on the temperature distribution. The combustor simulation delivers an insight into non-homogeneous temperature profiles in front of the turbine behind the transition channel of the silo-combustor. Finally, by adding leakages into the flow model, the interesting example of the non-homogeneous leakage of cold air, which can lead to local increase of material temperature, was simulated. All these simulations led to reliable silo-combustor upgrades.

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.

The GTX100 is the most recent industrial gas turbine in the ABB fleet. The development of the GTX100 turbine blading was a joint project involving four companies. A thorough evaluation of various design requirements resulted in the selection of a single shaft three-stage turbine configuration. The cooling techniques employed for the blading are based on the knowledge from the Russian school of design for gas turbines. These techniques have been verified by a considerable amount of experimental data and field experience over a number of years. To incorporate western manufacturing methods, western suppliers were introduced at an early stage in the development. Most of the engineering development of the turbine blading was carried out in Russia. In order to achieve efficient cooperation between Russia and Sweden, specialists from both companies were stationed at alternating companies. The verification of the turbine design is divided into two steps. The first step is cold and hot component testing and the second is the overall engine testing.

Currently CFD is extensively used in turbine and compressor blading design and analysis with numerous examples of CFD applications to be found in literature. At the same time, there are no reports about CFD simulation of secondary flows inside the turbomachine (e.g. cooling air transit, purge, etc). One probable reason is that the amount of air/gas involved in these flows is typically too small to have a direct impact on the engine performance. However, these secondary flows have a big impact on the heat transfer in cavities between structural components, and as a result have an impact on the thermal state, life of structural components, and clearances in the main flowpath. Therefore, the proper prediction of the flow between structural components is also an important part of the design procedure. In spite of the recent progress in computational hardware and software development, CFD simulation of flow between structural components remains still a challenging task due to very complex geometries, 3D turbulent flow structure with separations, reattachments and vortices. In addition to this, to be applied in design practice, the CFD code should satisfy certain important requirements, for instance the ability to automate the calculations in order to execute the analysis within a reasonable time and cost. Only recently has it become possible to satisfy this requirement, and now CFD starts to penetrate into design practices. This paper presents the experience accumulated within ALSTOM during the last few years in CFD simulation of flow between different structural components using commercial and in-house software. The following issues are presented: • Validation of numerical models; • Automation of numerical calculation; • Application examples (the flow in different cavities between casings and in rotor cavity).

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