10/1/2015 Taylor Tucker, MechSE Communications
MechSE assistant professor Kelly Stephani was recently selected as one of eight recipients for the
Written by Taylor Tucker, MechSE Communications
ECF challenges early career faculty to examine the theoretical feasibility of ideas and approaches that are critical to making science, space travel, and exploration more effective, affordable, and sustainable.
Stephani’s proposal, “A Phase-Space Coupled Hybrid Framework for Combined Continuum/Rarefied High Speed Flows,” focuses on NASA’s programmatic need for advanced aerothermodynamics modeling capabilities.
“This work introduces a transformative approach to modeling transitional flows, and we also plan to address a number of long-standing challenges related to hybrid flow solvers,” Stephani said.
The Computational Kinetics Group, Stephani's group of student researchers, will work with her to solve the problem. "We're building the fundamental tools to provide the critical link between kinetic theory (at the microscale) and meso/macro-scale processes related to complex high-speed entry flows," she said. Typically, Direct Simulation Monte Carlo (DSMC) is used for low earth orbit, but is very expensive computationally. Computational fluid dynamics (CFD) solvers are used at lower altitudes within the upper atmosphere, where the flow is continuum, but these descriptions tend to be inaccurate. The group's efforts will focus on establishing state-of-the-art simulation capabilities for high-velocity atmospheric vehicles under these conditions.
Flow structures that develop around high-speed atmospheric entry vehicles often contain localized flow regions where rarefied (or non-continuum) effects, within an otherwise continuum description, lead to significant modeling uncertainty. Hybrid techniques that incorporate both continuum and kinetic computational methodologies, however, offer an elegant balance of efficiency and accuracy for simulations involving mixed continuum/rarefied flow regimes.
Stephani will lead efforts to construct a foundational hybrid framework for chemically reacting flows from Generalized Chapman-Enskog (GCE) Theory. She anticipates a number of novel contributions from these efforts, including consistent state-based kinetics models for CFD/DSMC flow solvers, procedures for rapid assessment of continuum breakdown parameters for reacting flows, and a novel phase-space coupling procedure for improved statistics in DSMC tail-driven processes. (Phase-space is the coupling of physical space and velocity space. Each of these two spaces has three dimensions, with time being an additional possible dimension.)
“We’ll transfer information from one flow solver to the other flow solver while making sure that the models between them are physically the same,” Stephani said.
The ECF award will provide support of $600,000 over three years. “This award offers an incredible opportunity for my group,” said Stephani. “This is going to provide us with the human capital we need to tackle the challenges that we’ve set forth.”
NASA also encourages ECF recipients to initiate new collaborations. “We’ve arranged to work with collaborators at NASA Ames, NASA Langley, and at NASA’s Johnson Space Center toward the final stages of this work. We anticipate a number of opportunities for a direct technology transfer that will enable future exploration missions,” Stephani said. The collaboration will also be beneficial to students within the group, who will have opportunities to work with NASA.
“I am so incredibly grateful for this opportunity,” she said. “As an independent researcher, this is by far the most important accomplishment. This will help set the stage for future collaborations with other researchers, and put our group on a great trajectory for the foreseeable future.”