@article{zimmer_bolotnov_2021, title={Evaluation of Length Scales and Meshing Requirements for Resolving Two-Phase Flow Regime Transitions Using the Level Set Method}, volume={143}, ISSN={["1528-901X"]}, DOI={10.1115/1.4049934}, abstractNote={Abstract}, number={6}, journal={JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME}, author={Zimmer, Matthew D. and Bolotnov, Igor A.}, year={2021}, month={Jun} }
 @article{zimmer_bolotnov_2020, title={Exploring Two-Phase Flow Regime Transition Mechanisms Using High-Resolution Virtual Experiments}, volume={194}, ISSN={["1943-748X"]}, DOI={10.1080/00295639.2020.1722543}, abstractNote={Abstract Recent advancements in computing power allow utilization of state-of-the-art direct numerical simulations (DNSs), coupled with interface tracking techniques, to perform fully resolved simulations of complex two-phase flows, such as flow regime transitions. Studying the highly resolved temporal and spatial information produced from these virtual experiments can advance our understanding of the phenomenon and inform coarser models. With these improved models, better predictions of flow regime behavior and location in boiling water reactors can be made. The presented research uses the PHASTA code, which employs the level set method for interface tracking, to examine the mechanisms of flow regime transition, specifically the slug-to-bubbly and slug-to–churn-turbulent regime transitions. The DNS was validated using theoretical and experimental work found in open literature. Different geometries, including pipes and minichannels, were explored in order to improve the fundamental understanding of the complex flow phenomenon. Using advanced analysis techniques, the transient flow properties were analyzed at resolutions not available to other methods. The numerical data analysis allows for calculation of both time and spatially averaged properties as well as local instantaneous properties. Possible mechanisms for the transition are discussed. Examples include liquid kinetic energy/surface tension energy balance and interfacial shear forces in the liquid film. It is also noted that the transition out of slug flow can take at least two pathways: interfacial wave-induced instability development in the Taylor bubble, leading to its disintegration, or strong bubble shearing at the tail of the bubble.}, number={8-9}, journal={NUCLEAR SCIENCE AND ENGINEERING}, author={Zimmer, Matthew D. and Bolotnov, Igor A.}, year={2020}, month={Sep}, pages={708–720} }
 @article{zimmer_bolotnov_2019, title={Slug-to-churn vertical two-phase flow regime transition study using an interface tracking approach}, volume={115}, ISSN={["1879-3533"]}, DOI={10.1016/j.ijmultiphaseflow.2019.04.003}, abstractNote={Direct numerical simulation (DNS) coupled with an interface tracking method (ITM) is used to demonstrate the applicability of DNS to the study of vertical two-phase flow regime transition. The study focuses on the slug flow to churn-turbulent regime transition. PHASTA, a finite element based flow solver which utilizes the level set method for interface tracking, has been used to perform the presented simulations. A domain size study has been conducted in order to find pipe dimensions that match the natural wavelength of the periodic slug flow. A mesh resolution study has been completed. The results show that using DNS to simulate the slug-to-churn transition is within the capabilities of the code as the simulations agree well with experimental data and empirical knowledge. The simulations were analyzed to find flow features such as the velocity profile in the wake of a Taylor bubble and the bubble interface shape evolution during breakdown. An understanding of such features could help identify the driving physics behind the transition phenomenon.}, journal={INTERNATIONAL JOURNAL OF MULTIPHASE FLOW}, author={Zimmer, Matthew D. and Bolotnov, Igor A.}, year={2019}, month={Jun}, pages={196–206} }
 @article{talley_zimmer_bolotnov_2017, title={Coalescence Prevention Algorithm for Level Set Method}, volume={139}, ISSN={["1528-901X"]}, DOI={10.1115/1.4036246}, abstractNote={An algorithm to prevent or delay bubble coalescence for the level set (LS) method is presented. This novel algorithm uses the LS method field to detect when bubbles are in close proximity, indicating a potential coalescence event, and applies a repellent force to simulate the unresolved liquid drainage force. The model is introduced by locally modifying the surface tension force near the liquid film drainage area. The algorithm can also simulate the liquid drainage time of the thin film by controlling the length of time the increased surface tension has been applied. Thus, a new method of modeling bubble coalescence has been developed. Several test cases were designed to demonstrate the capabilities of the algorithm. The simulations, including a mesh study, confirmed the abilities to identify and prevent coalescence as well as implement the time tracking portion, with an additional 10–25% computational cost. Ongoing tests aim to verify the algorithm's functionality for simulations with different flow conditions, a ranging number of bubbles, and both structured and unstructured computational mesh types. Specifically, a bubble rising toward a free surface provides a test of performance and demonstrates the ability to consistently prevent coalescence. In addition, a two bubble case and a seven bubble case provide a more complex demonstration of how the algorithm performs for larger simulations. These cases are compared to much more expensive simulations capable of resolving the liquid film drainage (through very high local mesh resolution) to investigate how the algorithm replicates the liquid film drainage process.}, number={8}, journal={JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME}, author={Talley, Matthew L. and Zimmer, Matthew D. and Bolotnov, Igor A.}, year={2017}, month={Aug} }
 @article{hechavarria_terjesen_ingram_renko_justo_elam_2017, title={Taking care of business: the impact of culture and gender on entrepreneurs' blended value creation goals}, volume={48}, ISSN={["1573-0913"]}, DOI={10.1007/s11187-016-9747-4}, number={1}, journal={SMALL BUSINESS ECONOMICS}, author={Hechavarria, Diana M. and Terjesen, Siri A. and Ingram, Amy E. and Renko, Maija and Justo, Rachida and Elam, Amanda}, year={2017}, month={Jan}, pages={225–257} }