A Numerical Simulation Of Wet Steam Flow Based On Dual Fluid Model

Wet steam flow within steam turbine leads to lower efficiency and blade erosion. In essence, wet steam flow with spontaneous condensation is a non-equilibrium process, which could be sumerized in two aspects, the depature form themodynamic equilibrium and velocity slip between the droplets and vapor. Due to the mass, momentum, energy transfer caused by condensation, wet steam flow deviated from the equilibrium has an important impact on the flow within the steam turbine. If the non-equilibrium process could be described accurately, and considered in the design process, the efficiency of steam turbine could be improved.Based on the conception of dual fluid model and the characterictic of wet steam flow with spontaneous condensation, a dual fluid model for wet steam flow was established, which considers the velocity slip between two phases, mass, momentum and energy transfer caused by phase change between two phases. For the closure models of two phase turbulence, a modified realizable k-εmodel was established for the gas phase, and the turbulence viscosity of momentum equations for the liquid phase was setted equal to that of gas phase directly. Using FLUENT solver as the platform and UDFs provided by FLUENT, the dual fluid model mentioned above was implemented in FLUENT solver.For the dual fluid model created in this paper, numeriacal simulations in nozzle and two-dimensional cascade were implemented to verify its correctness. In order to consider the influence caused by non-equilibrium process and the velocity slip between the two phases on the downstream traverse total pressure of the vapor, two new models based on dual fluid model were also given in this paper. Spontaneous condensation was not considered for one of the new models and velocity slip was not considered for the other.On this basis, those two factors mentioned above could be considered separately.A three dimensional numerical simulation of wet steam flow with spontaneous condensation within a turbine stator by the dual fluid model was conducted at the last chapter of this paper. The focus of this numerical simulation is on how wet steam flow with spontaneous condensation could affect the downsteam traverse aerodynamic parameters for gas phase in three dimensional tubine stator.