The steam turbines play a significant role in global power generation. Especially, researchon low pressure (LP) steam turbine stages is of special importance for steam turbine man-ufactures, vendors, power plant owners and the scientific community due to their lowerefficiency than the high pressure steam turbine stages. Because of condensation, the laststages of LP turbine experience irreversible thermodynamic losses, aerodynamic lossesand erosion in turbine blades. Additionally, an LP steam turbine requires maintenancedue to moisture generation, and therefore, it is also affecting on the turbine reliability.Therefore, the design of energy efficient LP steam turbines requires a comprehensiveanalysis of condensation phenomena and corresponding losses occurring in the steam tur-bine either by experiments or with numerical simulations. The aim of the present workis to apply computational fluid dynamics (CFD) to enhance the existing knowledge andunderstanding of condensing steam flows and loss mechanisms that occur due to the irre-versible heat and mass transfer during the condensation process in an LP steam turbine.Throughout this work, two commercial CFD codes were used to model non-equilibriumcondensing steam flows. The Eulerian-Eulerian approach was utilised in which the mix-ture of vapour and liquid phases was solved by Reynolds-averaged Navier-Stokes equa-tions. The nucleation process was modelled with the classical nucleation theory, and twodifferent droplet growth models were used to predict the droplet growth rate. The flowturbulence was solved by employing the standard k-ε and the shear stress transport k-ωturbulence models. Further, both models were modified and implemented in the CFDcodes. The thermodynamic properties of vapour and liquid phases were evaluated withreal gas models.In this thesis, various topics, namely the influence of real gas properties, turbulence mod-elling, unsteadiness and the blade trailing edge shape on wet-steam flows, are studied withdifferent convergent-divergent nozzles, turbine stator cascade and 3D turbine stator-rotorstage. The simulated results of this study were evaluated and discussed together with theavailable experimental data in the literature. The grid independence study revealed thatan adequate grid size is required to capture correct trends of condensation phenomena inLP turbine flows. The study shows that accurate real gas properties are important for theprecise modelling of non-equilibrium condensing steam flows. The turbulence modellingrevealed that the flow expansion and subsequently the rate of formation of liquid droplet nuclei and its growth process were affected by the turbulence modelling. The losses wererather sensitive to turbulence modelling as well. Based on the presented results, it couldbe observed that the correct computational prediction of wet-steam flows in the LP turbinerequires the turbulence to be modelled accurately. The trailing edge shape of the LPturbine blades influenced the liquid droplet formulation, distribution and sizes, and lossgeneration. The study shows that the semicircular trailing edge shape predicted the smallestdroplet sizes. The square trailing edge shape estimated greater losses. The analysisof steady and unsteady calculations of wet-steam flow exhibited that in unsteady simulations,the interaction of wakes in the rotor blade row affected the flow field. The flowunsteadiness influenced the nucleation and droplet growth processes due to the fluctuationin the Wilson point.
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