Assessments of Bubble Dynamics Model and Influential Parameters in Microbubble Drag Reduction

摘要

During the course of this research effort computational parametric studies of the microbubble drag reduction phenomena were conducted. The effects of mixture density variation, free stream turbulence intensity, free stream velocity, and surface roughness on the microbubble drag reduction were studied using a single phase model based on Reynolds-averaged Navier-Stokes transport equations. Additionally, predictions of Eulerian multiphase model for microbubble laden flow were compared with Direct Numerical Simulation from the open literature. Good agreement was achieved between the simulations with the single phase model and experimental data of Deutsch et al. (2003). This good agreement was observed for both free stream velocity as well as surface roughness effect studies. Increased free stream turbulence intensity was observed to result in lower drag reduction, and this effect was stronger for higher density ratios of water and injected gas. For the same free stream velocity increase, the drag reduction was higher for higher density ratio. For fixed gas injection rate, lower drag reduction was predict for higher free stream velocity, and increased drag reduction was obtained with increased surface roughness. The drag reduction predicted by the multiphase model was substantially lower than that predicted by the Direct Numerical Simulation model of Ferrante and Elghobashi (2004). However, gas volume fraction and turbulent kinetic energy profiles predicted by the multiphase model were similar but not identical to those predicted by the DNS of Ferrante and Elghobashi (2004).