What is it about?
Fluid flowing through porous materials—like air moving through a forest canopy or fluid in industrial reactors—can sometimes move fast enough to become chaotic or "turbulent". Traditionally, scientists use complex computer models to calculate this turbulence, often assuming that the chaotic swirls of fluid can grow into large, macroscopic structures. To see if this assumption is accurate, we used extremely detailed Direct Numerical Simulation (DNS) to study how fluid moves through a microscopic matrix of perfectly arranged solid spheres. Our research discovered that the solid parts of the porous material actually physically block these turbulent structures from growing any larger than the pores themselves. Because of this, the complex mathematical equations normally used to calculate fluid stress (specifically, the Reynolds stress) are not actually needed. Instead, we propose that the flow can be modeled more simply by primarily looking at the drag caused by the fluid hitting the solid obstacles and the bounding walls of the container.
Featured Image
Photo by chris robert on Unsplash
Why is it important?
This work is important because it directly tests and challenges the underlying assumptions that engineers have relied on for years when building computational models for porous media. By proving that macroscopic turbulent structures are suppressed by the solid matrix, we show that many existing turbulence models overcomplicate the physics of the fluid flow. Practically, these findings allow us to simplify the governing fluid dynamics equations, saving significant computational time and resources. Our proposed model drops unnecessary calculations while keeping essential ones—like the Brinkman term, which accurately handles how the fluid interacts near solid boundary walls. This makes it much easier and more computationally efficient to model important industrial applications, such as developing new materials for thermal energy storage or improving bubble column reactors.
Perspectives
Working on this paper was a deeply rewarding experience because it allowed us to challenge long-standing assumptions in the fluid dynamics community. It is not every day that one gets to use high-fidelity Direct Numerical Simulation to look under the hood of macroscopic turbulence models and definitively show that some of the complex mathematics we have been using are largely unnecessary.I am particularly excited about the practical implications of our simplified model. By dropping the $k$ and $\epsilon$ equations while retaining the Brinkman term, we are offering engineers a much more efficient computational tool for everyday use. I hope this work encourages others to always question the default models in their simulation software and to look closely at the physical reality of the pore scale.
Andrey V Kuznetsov
North Carolina State University
Read the Original
This page is a summary of: Turbulence modeling for flows in wall bounded porous media: An analysis based on direct numerical simulations, Physics of Fluids, April 2017, American Institute of Physics,
DOI: 10.1063/1.4979062.
You can read the full text:
Contributors
The following have contributed to this page
