A PIV investigation of stratified gas–liquid flow in a horizontal pipe

Simultaneous Particle Image Velocimetry (PIV) measurements of stratified turbulent air/water flow in a horizontal pipe have been performed using water droplets as tracers in the gas-phase. The use of water droplets as tracers ensures that the water surface tension remains unaffected and thus allows small scale interfacial structures, such as capillary waves to occur naturally. Experiments have been conducted in a 31 m long, 100 mm diameter PVC pipe using air (density ' 1.20 kg/m3 and viscosity 18.4 µPa·s) and water (density 996 kg/m3 and viscosity 1.0 mPa·s) as test fluids. For the purpose of validation of the experimental set-up and the suggested seeding technique, single-phase measurements of both air and water were compared to each other and to DNS results provided by ”Wu X. and Moin P., 2008, A direct numerical simulation study on the mean velocity characteristics in turbulent pipe flow, J. Fluid Mechanics, Vol. 608.”, showing very good agreement. The two-phase measurements are presented in terms of mean- and rms-profiles. These measurements offer a qualitative demonstration of the behavior of the interfacial turbulence and its correlation with the various interfacial flow patterns. The observations made in this paper are in agreement with the conclusions drawn from the DNS study of ”Lakehal D., Fulgosi M., Banerjee S. and De Angelis, Direct numerical simulation of turbulence in a sheared air water flow with a deformable interface, 2003, J. Fluid Mechanics, Vol. 482.”. The present results may eventually provide a better explanation to many important phenomena related to the physical characteristics of stratified two-phase flow such as scalar mixing between phases, and to challenges related to its modeling