Numerical Investigation of Stationary and Instationary Two Phase Flows in Low Pressure Steam Turbines

This thesis describes the derivation of a collocated, coupled, pressure-based numerical framework for two-phase Euler-Euler flows. The governing equations are derived in detail to account for rotating frame, real gas physics and multiphase flows including phase change. In order to improve the numerical robustness compared to traditional segregated solution techniques, the conservation equations are assembled into a block coupled linearized equation system and solved simultaneously. The Navier-Stokes equations for two-phase flow are thoroughly reviewed for cross-coupling terms to reduce the explicit right hand side contribution. Based on this assembly method, a new, implicitly consistent momentum interpolation technique for multiphase flows is introduced. Apart from a coupled pressure-velocity formulation of the momentum and continuity equation, the conservation of phasic mass is implemented into a coupled coefficient matrix as well. Stabilization of this conservation equation is improved through implicit normalization, forced diagonal dominance and the coupled formulation of the phase change. Finally, the framework is extended to account for droplet nucleation and growth based on classical nucleation models. Validation is carried out using a series of test cases for real gas and multiphase flows. An outlook is provided to improve the droplet distribution description using population balance equations. Initial assessment using the MUSIG algorithm is provided at the end of the thesis.