My main subject of research is Fluid Mechanics. I am convinced that this discipline is of fundamental importance for both engineering and applied science. My research projects span across diverse interests including, two-pase flows, biological flows and other. Although my work is mainly experimental, I have also conducted numerical simulations and theory.

For details visit:  https://sites.brown.edu/zenit/

Two phase flows

I have devoted a good portion of my research interest to the study of bubbly and granular flows. For the case of granular flows, the complexity in determining the behavior of these
flows arises from the inelastic and frictional contacts among particles [1]. For bubbly flows, the hydrodynamic interactions among bubbles give rise to velocity fluctuations which, in turn, give a turbulent-like character to these flows [2]. In both cases, there have been significant developments over the last 15 years. My research group has actively participated in the collective effort to understand these systems better. We  continue investigating different aspects of these flows, including the effect of non Newtonian rheology in bubbly flows [3], the transition between viscous and collisional dominated regimes in liquid-solid flows [4], flow of bubbles in porous media [5], etc. In my view, for these core subjects progress is driven by the interest of understanding their fundamental nature, independently from having direct applications. However, due to their prevalence in many modern engineering applications, there is wide practical interest and many funding opportunities.

[1] G.G Joseph, R. Zenit, M.L. Hunt, and A. Rosenwinkel. Particle–wall collisions in a viscous fluid. J. Fluid Mech., 433:329–346, 2001.
[2] S. Mendez-Diaz, J.C. Serrano-Garcia, R. Zenit, and J.A. Hernandez-Cordero. Power spectral distributions of pseudo-turbulent bubbly flows. Phys. Fluids, 25:043303, 2013.
[3] R. Zenit and J. Feng. Hydrodynamic interactions among bubbles, drops and particles in Non-Newtonian liquids. Ann. Rev. Fluid Mech., 50:505–534, 2018.
[4] E. Linares-Guerrero, M.L. Hunt, and R. Zenit. Effects of inertia and turbulence on rheological measurements of neutrally-buoyant suspensions. J. Fluid Mech., 811:525–543, 2017.
[5] D. Hernandez, O. Chavez, A. Beltran, A. Garcia, B. Mena, and R. Zenit. Experimental study of the effect of wettability on the relative permeability for air-water flow through porous media. International Journal of Multiphase Flow, 120, 103091, 2019.

Biological Flows

The understanding of many biological systems cannot be completed without analyzing the fluid motion implied in them. The study of such flows give us an unique opportunity to explain many phenomena from a fundamental point of view. One approach is to study these systems replicating exactly the biological conditions in a controlled environment.
A better one is to simplify and model the problems by removing as many layers of complexity as possible, yet retaining the most relevant ones.

In my group we have studied the flow-structure interaction in biological heart valve prostheses [6] and the locomotion dynamics of microorganisms in
complex fluids [7, 8].

[6] R. Ledesma-Alonso, J.E.V. Guzman, and R. Zenit. Experimental study of a model valve with flexible leaflets in a pulsatile flow. J. Fluid Mech., 739:338–362, 2014.
[7] F. A. Godinez, L. Koens, T. D. Montenegro-Johnson, R. Zenit, and E.Lauga. Complex fluids affect low-Reynolds number locomotion in a kinematic-dependent manner. Exp. Fluids, 56:97, 2015.
[8] S. Gomez, F. A. Godinez, E. Lauga, and R. Zenit. Helical propulsion in shear-thinning fluids. J. Fluid Mech., 812:R3, 2017.

The fluid mechanics of artistic painting

Painting is, essentially a fluid mechanical problem. Much research has been devoted to understand the process of coating a solid surface with a fluid film, since most man-made surfaces are painted. In general, the objective of painting is to cover a solid surface with a thin and uniform layer of paint. For the case of artistic painting this is not exactly
the case. Artists aim to create coating textures of aesthetic value to express their views. Hence, they learn to manipulate the fluid and the process in unique ways. They do this in an empirical manner through experimentation and many trial-and-error repetitions. Through a series of recent projects, inspired by art historians, my research group has been involved in the understanding the physical principles of the painting techniques used by famous modern painters. We have studied the accidental painting technique by David Alfaro Siqueiros, [9], the dripping technique by Jackson Pollock [10] and we have many other ongoing projects in this subject.

[9] S. Zetina, F.A. Godinez, and R. Zenit. A hydrodynamic instability is used to create aesthetically appealing patterns in painting. PLOS One, 10:e0126135, 2015.
[10] B. Palacios-Muniz, S. Zetina, and R. Zenit. Pollock avoided hydrodynamic instabilities to paint with his dripping technique, PLoS One, 14 (10), e0223706, 2019.

• Member of the Academia Mexicana de Ciencias, 2003.

• Marcos Moshinsky Chair, Fundacion Marcos Moshinsky, 2012.

• Fulbright Scholar, California Institute of Technology, August 2014 to July 2015.

• Elected Member of the Academy of Engineering of Mexico. 2016.

• Fellow, American Physical Society.  2016.
• Simons Fellow, Isaac Newton Institute for Mathematical Sciences, November 2017.