Modeling of Shear-Driven Liquid Wall Films on Curved Surfaces - Effect on Accelerated Air Flow and Variable Film Load


Liquid wall films that are driven by the shear stress exerted from a co-current air stream occur in many technical systems, e.g. in rocket nozzles, heat exchangers and on steam turbine blades. They are also present in prefilming airblast atomisers which are used for the fuel preparation
in modern aviation gas turbines. In many cases an acceleration of the co-current air flow is imposed either in order to improve the performance or because of the geometrical constraints in complex configurations. Additionally, the film load Lf (volume flow rate per unit width) varies as a consequence of the contour of the flow passage, e.g. in concentric nozzles.
The film flow characteristics are strongly influenced by both effects which will be discussed in detail. In order to predict the two-phase flow field, a model has been developed which allows a fully coupled computation of the gas flow field and the liquid film.
The present paper highlights the main features of the model which allow to capture the effect of the imposed pressure gradient dP=dx and the varying film load Lf at the same time. It will be shown that the numerical approach is capable to predict the film propagation with a high accuracy, providing a powerful tool for the design and the improvement of technical applications where liquid film phenomena play an important role.