Simulations of FZR adiabatic air-water data with CFX-10

The CFD simulation of an adiabatic gas-liquid flow requires an adequate characterisation of the momentum exchange between the phases. This report describes the CFX simulation of adiabatic air/water bubbly flow in a vertical pipe and the comparison to experimental results for several test conditions that were obtained in FZ-Rossendorf. The measured cross sectional distribution of the gas volume fraction enables the validation of the applied models for the momentum exchange between the liquid and the gaseous phase. The drag bubble force determines the flow resistance in flow direction and influences the gas volume fraction for given superficial gas and liquid velocities. The non drag forces, namely the lift-, the wall- and the turbulent dispersion forces act perpendicularly to the flow direction and influence the cross sectional gas volume fraction distribution. Their correct simulation is important, since they have an essential influence on the flow regime.
In the report the model approaches for the drag and the non drag bubble forces are described. Several tests gained at MT-Loop that show low gas volume fractions are presented. These can be described by only one dispersed gaseous phase having a certain bubble size. These experiments are therefore suited for the validation of the non drag force models.
Increasing the gas injection rate, a bubble size distribution including bubble coalescence and fragmentation has to be considered. The paper describes the concept of the inhomogeneous MUSIG model, which is implemented in CFX-10. Several tests from MT-Loop and from TOPFLOW are presented to demonstrate the applicability of the model.
The simulations are intended for the comparison to other CFD models e.g. in the NURESIM-CFD platform.