Baseline model for simulation of bubbly flows

A key parameter appearing in closure relations for the Euler-Euler two-fluid model is the bubble size. A distribution of bubble sizes is established as a result of bubble-coalescence and -breakup processes. These processes are very complex and models are considerably less developed than e.g. for bubble forces and even bubble-induced turbulence. Therefore, a two-step procedure is adopted for model validation where in a first step measured values are substituted for the bubble size distribution. In this way the uncertainties of the less developed modeling for bubble-coalescence and -breakup are bypassed and a validation of the other parts of the overall model becomes possible. In a second step the previously qualified models for bubble forces and bubble-induced turbulence are used without any change and the validity of models for bubble-coalescence and -breakup can be assessed. This procedure is illustrated by application to a set of data obtained for vertical upward flow in a pipe. In the first step satisfactory agreement is achieved like in previous investigations. A first attempt at the second step shows promising results as well. From the observed level of agreement between simulation and experiment, issues requiring further investigation are identified.