Santiago J. Benavides

Research

Critical transitions in turbulence

With recent computational advances, careful parameter studies of turbulence transitioning from one regime to the other has become possible. This could be done by varying rotation, layer height, magnetic field strength, or more. These studies show surprising and unexpected behavior: in most cases, turbulent behavior changes sharply at a critical parameter value. Despite more and more studies finding the same critical behavior, an explaination for the existence of these critical points has yet to be found. My work aims to build upon the examples of these critical transitions, but also begin providing understanding for why they might exist to begin with.

Collaborators: Javier Jiménez, Miguel Bustamante, Alexandros Alexakis , Kannabiran Seshasayanan, François Pétrélis.

Transition to turbulence in wall-bounded shear flows

The transition from simple laminar flow to the chaotic and multi-scale turbulent state in many wall-bounded shear flows is subcritical: laminar flow remains linearly stable to perturbations, and the transition to turbulence occurs through the local proliferation of large-scale turbulent patches throughout the domain.

The phenomenon is inherently nonlinear and involves the nontrivial interaction of turbulent and laminar regions. Despite the success of models capturing the dynamics of these turbulent structures in pipe flow (with a single extended dimension), the large-scale organization of turbulent structures in planar geometries (with two extended directions), such as the bands seen in the picture on the left, remain a challenge. My research aims to create a simple 2D model for the turbulence and large-scale flow in plane Couette flow, aided by direct numerical simulations. Our work hopes to provide a clearer understanding of the structure and energy balance of an individual band, as well as to answer the question of why the patterns form, and what sets their orientation and wavelength.

Collaborators: Dwight Barkley, Laurette Tuckerman

Sediment transport near the threshold of motion

Sediment transport by wind or water near the threshold of grain motion is characterized by rare but large transport events. This intermittency makes it difficult to relate average bed load sediment flux to average flow conditions, a common approach in the study of sediment transport, or to define an unambiguous threshold for grain entrainment. Although intermittent sediment transport has been observed, previous studies have struggled to explain its presence or reproduce it. Through a series of flume experiments and idealized numerical simulations, my work aims to understand the dynamics of sediment transport near the threshold of motion, to describe the presence of intermittency, and understand its consequences.

Collaborators: J. Taylor Perron, Eric Deal, Jeremy G. Venditti

Turbulence in the transition region of gas giant planets and exoplanets

Ionization occurs in the upper atmospheres of hot Jupiter exoplanets and in the interiors of gas giant planets, leading to magnetohydrodynamic (MHD) effects which couple the momentum and the magnetic field, thereby significantly altering the dynamics. In the transition region between the hot, ionized interior and cold, neutral region, one finds moderate temperatures such that the gas is only partially ionized and very poorly conducting. The transition region acts as a bottom boundary for the atmospheric jets seen on the surface, and as a top boundary for the magnetid-field generating dynamo region. It therefore likely affect things like the depths of the jets or the morphology of the magnetosphere. In my work, I use idealized turbulence simulations to understand how the particular characteristics of this region (partial ionization and weak conductivity) affect the dynamics and could therefore influence the formation of jets and more.

Collaborators: Glenn R. Flierl, Keaton J. Burns, Basile Gallet

Journal publications & preprints

• "Model for transitional turbulence in a planar shear flow,"
  Benavides, S. J., & Barkley, D. (arXiv), 2023. [preprint] [Supplemental Movies (zip file)]
• "Discrete simulations of fluid-driven transport of naturally shaped sediment particles,"
  Zhang, Q., Deal, E., Perron, J. T., Venditti, J. G., Benavides, S. J., Rushlow, M., & Kamrin, K. (ESS Open Archive), 2023. [preprint]
• "How fast or how many? Sources of sediment transport intermittency,"
  Benavides, S. J., Deal, E., Venditti, J.G., Zhang, Q., Kamrin, K., & Perron, J. T. Geophysical Research Letters, 50, e2022GL101919, 2023. [preprint] [doi]
• "Grain shape effects in bed load sediment transport,"
  Deal, E., Venditti, J.G., Benavides, S. J., Bradley, R., Zhang, Q., Kamrin, K. & Perron, J. T. Nature, 613, 298-302, 2023. [preprint] [doi]
• "Effective drag in rotating, poorly conducting plasma turbulence,"
  Benavides, S. J., Burns, K. J., Gallet, B., & Flierl, G. R. The Astrophysical Journal, 938, 92, 2022. [arxiv] [doi]
• "Fluid-driven transport of round sediment particles: from discrete simulations to continuum modeling,"
  Zhang, Q., Deal, E., Perron, J. T., Venditti, J. G., Benavides, S. J., Rushlow, M., & Kamrin, K. JGR: Earth Surface, 127, e2021JF006504, 2022. [preprint] [doi]
• "Inverse cascade suppression and shear layer formation in MHD turbulence subject to a guide field and misaligned rotation,"
  Benavides, S. J., Burns, K. J., Gallet, B., Cho, Y-K., & Flierl, G. R. Journal of Fluid Mechanics, 2022. [arxiv] [doi]
• "The impact of intermittency on bed load sediment transport,"
  Benavides, S. J., Deal, E., Rushlow, M., Venditti, J.G., Zhang, Q., Kamrin, K., & Perron, J. T. Geophysical Research Letters, 49, e2021GL096088, 2022. [preprint] [doi]
• "Symmetry breaking in a turbulent environment,"
  Alexakis, A., Pétrélis, F., Benavides, S. J., & Seshasayanan, K. Phys. Rev. Fluids, 2021. [arxiv] [doi]
• "Two-dimensional partially ionized magnetohydrodynamic turbulence,"
  Benavides, S. J. & Flierl, G. R. Journal of Fluid Mechanics, 2020. [arxiv] [doi]
• "Critical transitions in thin layer turbulence,"
  Benavides, S. J. & Alexakis, A. Journal of Fluid Mechanics, 2017. [arxiv] [doi]
• "On the edge of an inverse cascade,"
  Seshasayanan, K., Benavides, S. J. & Alexakis, A. Physical Review E, 2014. [arxiv] [doi]

• May 2, 2023 I am very pleased to announce that I have received the Marie Sklodowska-Curie European Postdoctoral Fellowship! I will be working with Javier Jiménez at the Universidad Politécnica de Madrid and Miguel Bustamante at the University College Dublin on "Elucidating the bidirectional energy cascade of geophysical turbulence in time, space, and scale". I am very excited to begin in September of 2023.
• January 25, 2022 My paper with Keaton Burns, Basile Gallet, James Cho, and Glenn Flierl, Inverse cascade suppression and shear layer formation in MHD turbulence subject to a guide field and misaligned rotation, has finally been published in the Journal of Fluid Mechanics. Take a look here!
• December 15, 2021 I successfully passed my thesis defense! Send me an email if you are interested in a copy of my thesis. It's been a great five and a half years at MIT; I've learned and grown so much! I'm so thankful for all of the support I've had from my friends, advisors, and my partner during this time. I will miss Boston, but I am very excited to get going on the next step!
• December 13, 2021 I can finally officially announce that I have accepted a post doc position at the University of Warwick, where I will work with Dwight Barkley and Laurette Tuckerman on problems related to transition to turbulence in wall-bounded shear flows.
• August 11, 2020 My first PhD paper with Glenn Flierl, Two-dimensional partially ionized magnetohydrodynamic turbulence, has finally been published in the Journal of Fluid Mechanics. Take a look here!
• June 15, 2020 I am honored to have been awarded NASA's Future Investigators in NASA Earth and Space Science and Technology (FINESST) fellowship , which will fund me for my last year of my PhD!
• June 13, 2020 My article with Glenn Flierl on "two-dimensional, partially-ionized, magnetohydrodynamic turbulence" has been accepted by the Journal of Fluid Mechanics for publication.
• June 1, 2020 Day 1 of summer mentorship! This summer I will be mentoring and working with two undergraduate research interns from MIT, who will be working on a project with Glenn Flierl and I on rotating convection. I look forward to teaching them about fluid dynamics, convection, and numerical simulations, but most importantly I look forward to collaborating with future scientists in the field!