CARPET 5:
Experiments on near-interface flow phenomena

Objectives:

To perform critical experiments on local phenomena near interfaces in stratified flow of liquid/liquid/gas in horizontal and near-horizontal flow. The work is intended to result in better predictions for "slip velocities" between phases, break-up of the interface, and to improve our insight into boundary layers adjacent to free surfaces for supplying "wall laws" as closure relations for computational treatment of such layers. In addition, we will study the formation and evolution of droplets at liquid/gas interfaces in shear flows; both in steady state and transient mode. This includes instability aspects and break-up of the interface.

Background:

In many situations in process- and transport engineering, interfaces are exposed to high shear stresses at turbulent flow conditions. This may lead to instabilities and break-up. Droplets may be generated and carried into the gas phase with possibilities for coalescence and further break-up. Criteria for primary instabilities and break-up need to be established, along with the turbulence structures close to the interfaces in normal, smooth modes. This requires experimental work combined with more detailed fluid dynamics modelling of the actual velocity distributions through each of the phases.

Eventually, such models must contain turbulence at large, and close to the interfaces in particular. CFD-results for the latter regime are now emerging, and there is an apparent need for detailed basic experiments to validate models and to provide closure relations. Also, in separation technology (water from oil), the evolution of droplet dispersions along interfaces is crucial, all the way from equilibrium turbulent shear flow and to gravitational settling in otherwise stagnant conditions.

Scope of work:

To perform LDV- and hot film experiments to measure primarily local velocity profiles and turbulence characteristics near liquid/gas and liquid/liquid interfaces in two- and three-phase horizontal flow. The experiments will also focus on the behaviour of droplet dispersions along interfaces by means of optical probes and PIV. The flow will be established in a laboratory test loop of 8 m length and with a rectangular test section 70 mm x 70 mm that has been recently constructed. The initial program will be carried out for water and gas, using air at atmospheric conditions for the gas. Later SF6 gas may be introduced in the system at pressures up to 5 bar to simulate the effects of dense gases. The work is complementary to numerical modelling activity in the proposed research program, (LES and Navier-Stokes simulations) and the results must be interpreted in relation to models, both of the engineering one-dimensional type and of the detailed distributed type.

PhD student:

Maria Fernandino

Affiliation:

NTNU, Department of Applied Mechanics, Thermo- and Fluid Dynamics.

Supervisors:

Tor Ytrehus in colloaboration with Hallvard F. Svendsen, Trond Kvamsdal, Stein T. Johansen, John Morud , and Leif R. Hellevik.