Two-Zone PIV Analysis of Wavy and Wavy-Annular Two-Phase Flow

Cross-sectional thin film micro-particle image velocimetry (cTFMPIV) analysis has been performed for air-water two-phase flow in a 19.05 mm horizontal duct. Images were captured by introducing a light sheet from a Nd:YAG laser into the flow, with the fluorescent emissions from three micron particles captured by a CCD camera behind a microscope objective and red filter. These images were grouped into pairs and digitally enhanced to isolate particle traces using commercial image processing software. Image pairs were collected for five air flow rates at each of four water flow rates and separated into base film and wave zones for PIV analysis. Using DaVis 7.1 (LaVision GmbH), vector maps were obtained for each pair. Less than 2% of the image pairs were removed due to clearly spurious vectors, while the appropriate zone for less than 8% of the image pairs could not be determined These pairs were grouped into a third batch. The vector maps were analyzed to calculate velocity profiles and turbulence (fluctuation) statistics in terms of wall coordinates. These statistics included intensities and Reynolds stresses. The base film shows laminar behavior beyond what would be expected from the universal velocity profile. The wave zone displays significantly different behavior and appears to reach an asymptote rapidly. Calculation of fluctuation intensities indicates a maximum within the wave zone along the gas-liquid interface, while the distribution of radial fluctuations in the base film and axial turbulence in all zones is approximately uniform. Calculation of the u^′v^′ shear Reynolds stress suggests that it has a negative value.