The goal of the proposed research is to experimentally and theoretically explore the transition from laminar to turbulent flow in the case of two phase flow in a pipe. While a lot of prior work has been done on transition for single phase fluids, the theme of this proposal is largely unexplored. The proposed work will have an impact on understanding the fundamental notions in transition to turbulence when one of the two phases is dispersed in the other. The technological applications of this work are important, most notably in the process of 3D printing and in additive manufacturing.
Recent experiments on pipe flows suggest that the critical Reynolds number for transition can either be shifted to significantly lower values or delayed to much higher values when a liquid flow includes a second phase of immiscible liquid drops or rigid particles. The direction of the shift depends on the volume fraction of the discrete phase as well as the ratio of pipe-to-particle diameter. The physical mechanisms behind these transition changes are unknown. The objective of the proposed research is to uncover and characterize these mechanisms through experimentation and analysis. It is hypothesized that at least two mechanisms are present: larger drops or particles can promote instabilities caused by local differences between the particle and surrounding fluid velocity, and smaller drops or particles can suppress growth of or otherwise disrupt larger scale instabilities and coherent structures. Experiments are planned in a transparent pipe facility where critical Reynolds number will be determined for liquid/liquid and liquid/solid dispersions. Results will be analyzed to determine time evolving flow features, ensemble averaged statistics, and dynamically significant modes associated with transitional flow structures, and ultimately the specific mechanisms affecting transition. The educational activities proposed include undergraduate and graduate student involvement in research, engagement with elementary school teachers to develop science curriculum, and outreach activities ranging from actively mentoring female high school and college students to meetings of the PI with members of Congress in order to promote science and engineering.
