Ash deposition on turbine blade surfaces is studied in this work using a particle deposition model. The model involves the three main processes: particle transport to the blade surface particle sticking at the surface and particle detachment from the surface. The model is used to investigate the effect of ash particle deposition on the flow field through turbine cascades. The surface velocity and the downstream total pressure coefficient are calculated for the clean and the fouled blade profiles and used in this investigation. The profile of the clean blade is chosen from the literature for which flow field measurements are available. The two dimensional compressible flow field is solved for the clean blade using the RNG k-ε turbulence model with the two layer zonal model for the near-wall region. The results are compared to the experimental data. The flow field is solved at the conditions expected in modern gas turbines. The deposition distribution on the blade surface is calculated during three periods of 12 operating hours each assuming inlet particle concentration as 100 ppmw. The fouled blade profile is predicted after each period. Then the flow field and deposition calculations are repeated to account for the time-dependent particle deposition. The flow field is calculated for the fouled blade after operating hours and investigated using the experimental data and the numerical calculations of the clean blade. The profile loss of the fouled blade is also predicted and compared to that of the clean blade.

One of the main mechanisms that control particle movement is the turbulent diffusion by which the particles in the turbulent boundary layer migrate to the surface under the influence of random flow fluctuations. Theoretical approaches to particle dispersion use random walk models to represent the effect of turbulent fluctuation velocity on particle movement. As a consequence, the turbulence model has a significant effect on the particle trajectory. Particle sticking probability, on the other hand depends upon the particle impact velocity. Moreover, the wall shear stress that is calculated from the turbulence model is the main cause of particle detachment from the surface. In this work, the effect of turbulence models on particle dispersion, deposition on turbine blade surfaces and detachment from the surfaces is studied. Two turbulence models have been tested: the Renormalization Group (RNG) k-ε model and the standard k-ε model. The near-wall region is solved by two different models: the standard wall function and the two-layer zonal model. It is found that the RNG k-ε model with the two-layer zonal near-wall model is the more appropriate turbulence model for particle deposition. It is also concluded that the standard wall function should not be used when solving the flow field near the wall for particle deposition. The reason is that this method does not give the detailed solution of the flow near the wall that is very important for deposition models.

The design of modern gas turbines requires the predetermination of their dynamic behavior during transients of various kinds. This is especially true for air storage and closed cycle gas turbine plants. The present paper is an introduction to a computatational method which permits an accurate simulation of any gas turbine system. Starting with the conservation equations of aero/thermodynamics, the modular computer program COTRAN was developed, which calculates the transient behavior of individual components as well as of entire gas turbine systems. For example, it contains modules for compressors, turbines, combustion chambers, pipes etc. To demonstrate the effectiveness of COTRAN the shut-down tests of the air storage gas turbine plant Huntorf were simulated and results compared with experimental data. The agreement was found to be very good.

The present study was done to investigate the performance differences in terms of thermal efficiency and specific power output of: • combined cycle power plants with integration of low temperature regenerative heat, standard gas turbines operated in wet cycle mode, turbo expanders and steam turbines (here: alternatives) • combined cycle power plants with integration of low temperature regenerative heat, wet cycle adjusted gas turbines and steam turbines (here: basic power plants or basic cycles) • standard combined cycles. The term 'adjusted' means that the blading of either the compressor or the turbine of a standard gas turbine was modified to accommodate the mass flow difference between the two. The analysis shows that in terms of thermal efficiency the alternatives are equal to or better by about 5%-points than the basic power plants. On the other hand, the corresponding specific outputs are lower by about 25 to 30%. But the gas turbines of the alternatives are the existing standard designs (see above) and, therefore, less expensive. Comparing the alternatives with the standard combined cycles, it is observed that the alternatives have a thermal efficiency advantage of up to 20%-points and a specific output advantage of up to 50%. Both of them are due to the integration of low temperature regenerative heat by injection of hot water into the alternative cycles and the definition of the thermal efficiency as based on the fuel burnt.

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