Simone Tandurella et al
A rendering of fluid simulation involving 100,000 spherical particles in a 3D fluid grid with hundreds of millions of points falling due to gravity
How fast does smoke rise, rain fall, and a supernova explode? Fluid simulation on an unprecedented scale provides a new set of scientific tools for fundamental physics and applied fluid engineering.
What determines the speed what do raindrops fall, with which sediments are deposited in river estuaries, or matter is ejected during a supernova explosion?
These questions revolve around a factor that is deceptively simple but deceptive: the rate at which a fluent with particles mixes with another without particles.
In practice, how do hundreds of thousands of bodies interact with each other?
The rain drops pass from one layer of air to another; sediments fall from the river into seawater; and the ejected material passes through the surrounding dust cloud from the exploding star.
The same principle dictates the mixing of sediments in rising smoke, dust storms, nuclear explosions, hydrocarbon refining, metal smelting, wastewater treatment, among many other processes.
New simulations have now given researchers and engineers unprecedented access to these fundamental mechanisms of fluid mechanics. Although the phenomenon is clearly visible in everyday lifehas escaped scientific scrutiny due to its complexity.
In the new study, led by researchers at the Okinawa Institute of Science and Technology (OIST) and the University of Turin and published last week in Physical Review Letters, researchers have for the first time derived a general formulation about how layers of heavy particles mix, and described the common characteristics of these phenomena.
“Both the simulations and the model we obtained pave the way for exciting investigations into a wide range of phenomena in fundamental physics, as well as applied research in fluid engineering,” he explains. Simone TandurellaOIST researcher and first author of the study, in .
Although the general laws of physics that govern the behavior of most fluids are relatively simple, solving the equations to predict this behavior is extremely complicated.
At first glance, the study of sediment fall should be simple, but scientifically describe the mechanics by which individual grains of sand descend to the bottom of a river — or even the overall mixing rate between sediment-laden water and clean water — is complicated by the enormous complexity of the forces involved and the unpredictability of long-term interactions.
Among these factors are the weight and volume displaced for each particle, the way each particle drags liquid with you due to friction, the influence of gravity or any other acceleration field, and the way the presence of one particle affects all others around it.
As Tandurella summarizes, “if the world is already famous for its complexity, imagine the problem of 100 thousand bodies”.
To capture this complexity, which cannot be rigorously reproduced and studied experimentally, and which was previously thought impossible to represent computationally, the team simulated the movement of 100 thousand particles three-dimensional elements suspended in a fluid composed of hundreds of millions of points.
Simone Tandurella et al
“For each solid particle, with its own volume and weight, we calculate the forces it exerts through its surface on surrounding points in the fluid, and the way in which those points exert force on the particle. We then add up the forces for each particle, simultaneously solve the fundamental Navier-Stokes equations of fluid motion across the entire grid, and move forward one step. This is done over millions of steps”, says Tandurella.
One of the phenomena that the team observed through the simulations was the formation of sediment plumes: As heavy suspended particles sink under the action of gravity, drag the fluid with them surrounding area due to friction.
This downward-moving fluid then pulls in other particles nearby, which in turn move more fluid, leading to the formation of a sediment plume. The feather displaces an equivalent volume of fluid clean, which rises at an equivalent rate and pushes even more sediment-laden fluid downward.
And, because the terminal velocity of a particle is relative to the fluid around it, the particles in the center of the plume progressively accelerate to ever greater speeds, activating a feedback mechanism which also increases the overall mixing rate.
“These phenomena could not have been observed with previous simulations, which neglected complete interactions between particles and fluid. This is the first time that we have been able to reproduce and study these behaviors rigorously”, highlights Marco Rosti, professor at OIST and co-author of the study.
Armed with these simulations and the theoretical framework necessary to accurately describe the speed of sediment mixingresearchers now have better access to a wide range of fundamental phenomena from physics and other areas, as well as applied research in fluid systems.
As practical applications of the study They range from optimizing flows in wastewater treatment or chemical refining processes to waterway engineering or environmental protection against soil carryover, among many other possibilities.
