Reliable prediction of multiphase turbulent flows using computational fluid dynamics (CFD) is important in a wide range of engineering applications (e.g., flows in nuclear reactors, chemical processing plants, heat exchangers etc). While some multiphase flows can be successfully modeled, many questions remain unanswered regarding the interactions between bubbles and the turbulence. Specifically, multiphase CFD approaches utilize interfacial forces (e.g., lift, drag forces) to predict the bubble distribution in the flow. However, the influence of the turbulence on the interfacial forces is not fully understood.
Intellectual Merit : The project objective is to quantify bubble/turbulence interactions in a specific set of flow conditions by analyzing experimentally validated interface tracking simulations and to create new turbulence spectrum that accounts for interfacial forces to be used in multiphase CFD and multiphase large-eddy simulations (LES). Advanced finite-element based flow solver (PHASTA) with Level-Set method for interface tracking will be used to perform the bubble/turbulence interaction studies. This code has been successfully applied to large scale direct numerical simulation (DNS) of turbulent flows in various geometries, as well as interface tracking simulations (including bubbly channel flow, annular flow). The proposed research will test the following hypotheses: (i) Bubbles deposit energy to the liquid turbulence eddies of the same size and deformability of a bubble controls the amount of energy, and may result in reverse energy transfer from the liquid turbulence; (ii) The energy deposition into the liquid turbulence is affected by the presence of the wall and the bubble/wall interactions modify the law of the wall and affect shear-induced energy production; (iii) The lateral bubble distribution in turbulent shear flow is governed by interfacial forces which strongly depend on bubble/turbulence interaction.
Broader Impacts : The success of this project will be instrumental in developing new multiphase flow models that have the ability to design advanced engineering systems with multiphase CFD. More accurate models for this type of flows can allow the construction of more efficient nuclear power plants, chemical processing plants as well as bring two-phase flow applications in other areas of engineering. High-fidelity interface tracking simulations will be introduced in graduate level courses on thermal hydraulics in the Nuclear Engineering Department. In addition, basic concepts related to the proposed research will be presented to high school students through the yearly Young Investigator's Summer Program in Nuclear Technology organized by the Nuclear Engineering Department's Outreach Program.
