One-dimensional models of multiphase flow in pipes are based on averages over the pipe cross section, and traditional models rely on bulk velocities, i.e., a single, uniform velocity for each fluid layer. The OLGA HD stratified flow model provides a significant improvement by re-introducing the two-dimensional velocity profile in the pipe cross section.
In this work, we compare the velocity profiles determined by OLGA HD against measured data from two-phase oil-water experiments. Additionally, we will show that good pressure drop predictions can be obtained even when there is a mismatch between calculated and measured velocity profiles over large portions of the cross section.
One-dimensional models of multiphase flow in pipes are based on rigorous balances for the conservation of mass, momentum, and energy in terms of average values over the pipe cross section. While these equations themselves are derived from first principles, closure models (or correlations) are required to address terms related to friction as well as dispersions accounting for the mixing of phases, and these closures introduce a degree of uncertainty into the models. The conservation balances ensure that basic physical quantities are conserved and that they provide qualitatively correct predictions, however, proper friction models are required to produce results that are quantitatively correct.
The OLGA HD stratified flow model was developed to meet the needs for reliable predictions of pressure drop and liquid content in ultra-long gas-condensate pipelines (see Biberg, et al.  for a comprehensive description of the model). To improve predictions over traditional flow models, the concept adopted is to incorporate more physics into the flow description, rather than to rely directly on correlations.