[en] A mixing length turbulence model is used to study the distribution of liquid and gas in the core of an annular two-phase flow. The gas volumetric fraction distributions were obtained for different regions of the core and then combined to obtain the distribution for the entire region. In vertical upflow a peak in the volumetric fraction distribution is predicted close to the liquid film interface for some range of flow parameters, while in downflow the peak is predicted at the pipe centerline. Larger interfacial shear stresses have the effect of increasing the gas phase concentration close to the liquid film interface and larger values of the average void fraction produce more uniform profiles in both upflow and downflow. By comparing the predictions of the model with the upflow and downflow air-water experimental data of different diameter tubes, the turbulence parameters are explicitly identified and it is shown that the model predicts well the experimental data over a wide range of liquid and gas mass flow rates