Investigation of drag and virtual mass coefficients for rising ellipsoidal bubbles

Accurately describing drag and virtual mass forces in two-phase flows is crucial for high fidelity modeling of nuclear thermal hydraulic safety systems. This study evaluates existing drag coefficient, C_D correlations commonly used in computational fluid dynamics (CFD) applications for a single air bubble rising in water and compares model predictions to an experimental database for ellipsoidal air bubbles of varying diameters with velocity field measurements obtained with particle image velocimetry (PIV). An experimental flow loop has been built to inject air bubbles of varying diameter into an optically clear acrylic test section. The PIV system used a double pulsed Nd:YLF laser, a SpeedSense M320 High Speed Camera with a 400 Hz acquisition frequency, and Rhodamine-B fluorescent seeding particles. Counter-current flow was used to stabilize bubble rise and to increase time within the field of view. A range of ellipsoidal, distorted, and cap bubbles were injected. Results provide a comparison between experimental data and existing drag coefficient correlations. An uncertainty analysis for the velocity field measurement is presented. Improved measurements with quantified uncertainty are crucial to perform a rigorous uncertainty analysis in computer codes using these correlations. The data collected has the potential to be used in code verification for CFD applications.