Particle image velocimetry measurements in stratified air/water flow in a horizontal pipe

摘要

A technique for detailed velocity measurement in a thin wavy liquid layer in stratified gas/liquid pipe flow has been developed. The technique combines PIV with profile detection, and it results in phase-averaged velocity profiles which can be used to find all the components of a decomposed velocity field. Two cases were studied, one with a laminar and one with a turbulent liquid layer, both having a wavy interface. The interface statistics and shapes reveal a similarity with the pure capillary wave solution of Crapper (18), which is yet for deep water. The measured average velocities are seen to obey the established law-of-the-wall for single-phase pipe flow very close to the wall only, while in the rest of the layer they were modified due to presence of the waves. The phase-averaged velocity profiles arc typical of waves superimposed on a base flow; when the mean flow is subtracted, the wave-induced velocities remain, which compare favourably with the predictions by the linear wave theory, except at the interface where deviations arc observed due to wave irregularity. The separation of the pure turbulent motion, however, was more difficult to achieve. The turbulence profiles contained spurious fluctuations which arc due to waves having a range of wavelengths and amplitudes.