Both experimental and three-dimensional CFD investigations are carried out in a scale model of an industrial gas turbine exhaust system to better understand its complex flow field and to validate CFD prediction capabilities for improved design applications. The model consists of an annular diffuser passage with struts, followed by turning vanes and a rectangular plenum with side exhaust. Precise measurements of total/static pressure and flow velocity distributions at the model inlet, strut outlet and model outlet are made using aerodynamic probes and locally a Laser Doppler Velocimeter (LDV). Numerical analyses of the model internal flow field are performed utilizing a three-dimensional Navier-Stokes (N-S) calculation method with the industry standard k-ε turbulence model. Both the experiments and computations are carried out for three load conditions: full speed no load (FSNL), full speed mid load (FSML, 57 percent load), and full speed full load (FSFL). Based on the overall comparison between the measurements and CFD predictions, this study concludes that the applied N-S method is capable of predicting complicated gas turbine exhaust system flows for design applications.

The proper design of the compartment ventilation system is an important requirement in the gas turbine industry. A poor ventilation system not only causes a circumferentially nonuniform casing temperature distribution, but also allows the formation of dangerous gas pockets inside the enclosure. Further, the presence of a circumferential casing temperature gradient has a negative impact on the operational efficiency of the turbine. Keeping the above design objectives in mind, a three-dimensional CFD analysis has been carried out using a leading commercial code to analyze the effectiveness of GE MS5002E ventilation system. A detailed geometric model is developed by including the entire turbine casing, various pipelines, surfaces of inlet and exhaust plenums, roof (with ventilation air inlets and outlet) and walls. Surfaces of all the components in the auxiliary compartment are also captured in the model. For easy meshing, the gas turbine compartment is divided into five regions: 1) inlet plenum and inlet case, 2) compressor, 3) compressor discharge case, 4) HPT and LPT, and 5) exhaust plenum. After meshing, these regions and the auxiliary compartment are combined using arbitray interfaces. A steady incompressible, high Reynolds number k-ε turbulence model is used in the present analysis. Except the casing external surfaces, temperatures are specified on the surfaces of various components, pipes, enclosure inside walls and roof. The casing temperature is determined using conjugate heat transfer modeling in which convective boundary conditions are stipulated on the casing interior surfaces and conduction through casing walls is solved as a part of the CFD solution. Radiation boundary conditions are applied on the casing external surfaces, enclosure walls and roof. Most of the pipes are included in the model. Small regions are modeled as porous media. Buoyancy effects are accounted in the model. The present CFD results will be used in conjunction with prototype testing to optimize the ventilation layout.

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