Development of a model for thin films and numerical sensitivity tests

Abstract

Because the unsteady behavior of liquid films in steam turbines is a key point for additional friction losses and atomization process (that leads to coarse water generation), the development of a dedicated model has been found necessary. A two-dimensional computational fluid dynamics code for unstructured mesh is being developed using the finite volume method to simulate this thin liquid film. The aim is to predict the formation of the waves in the film since it is suspected to be a key parameter for friction and atomization. Applied as a first step to a plane plate, the code has been verified in a one-dimensional version with analytical solutions and is tested in low-pressure turbine steam conditions. Falling films computations (without gas shear stress) show that the model is capable to reproduce the waves’ shape of experiments from the literature. With steam under low-pressure turbine conditions, and compared to experimental data from the University of Michigan, the model including shear stress and surface tension provides good results for heights. Sensitivity calculations have been undergone showing the crucial influence of the surface tension and the generation of solitary waves for high velocities is captured by the code. The effect of gravity is also quantified.