An in-depth study of electric fields in sandstorms

One of the lesser-known aspects of sandstorms is their ability to generate high-magnitude electric fields, as well as the ability to disrupt communications equipment.

This complex phenomenon has baffled researchers since the nineteenth century. Today, recent studies have shown that sand can pick up static electricity through collisions that occur near the ground. However, there is less certainty about how the electrified sand will behave once it is in the air. The observed field strength requires some means to separate oppositely charged particles from one another over large scales.

In the KAUST laboratories, accurate modeling was performed using a simulation framework developed by KAUST scientists. Professor Ravi Samtani, professor of mechanical engineering at the university, and his team realized that because there are so few collisions between sand particles in the atmosphere, another physical mechanism is involved in creating the electric field. They hypothesized that turbulence – the random movement of sand particles embedded in the air flow – might cause sand grains to spontaneously separate. except if; Proving this theorem requires some means of simplifying a problem centered with many dynamic variables.

This is what Samtani points out: “It would require unrealistic computing power to separate all those sand particles and turbulent motions.” He adds, “Therefore, we use the so-called big vortex simulation, whereby small fluctuations or vortices are mitigated and only large fluctuations or vortices remain. And we put the model inside the sandstorm, for a few minutes or hours, to see what’s statistically consistent.”

Samtani believes that simulation of large eddies will be the future of computational fluid dynamics in industrial and aerodynamic applications. It should be noted that meteorologists have used the strategy of simulating large eddies for many years in order to predict the weather.

Furthermore, Mostafa Rahman joined Samtani Group; To investigate this problem, as part of his Ph.D. thesis research. He also helped develop an approach in which turbulent vortices of sandstorms are formed within a hypothetical box, extending from ground level to kilometre-highs in the atmosphere. From here, they controlled the intensity of the sandstorm using an algorithm that inserts different densities of charged particles into the box, just above the desert floor.

With some explanation, Rahman says: “At the close to the ground, turbulent air is associated with the transfer of sand and affects each other, and these mechanisms are confusing in terms of design based on the use of traditional techniques.”

The team spent months modeling and programming on the KAUST supercomputer (Shaheen 2) to solve vortices large enough in detail. Their calculations show that the smaller grains tended to follow the turbulent flow, but the larger grains did not. Since the small and large sizes of sand grains have opposite charges, this turbulence-based separation generates an electric field that protects itself and enhances the charge separation process. This ultimately results in the production of electric fields approaching about several hundred thousand volts per meter, which precisely matches the field measurements.

This is confirmed by Samtani when he says: “The reproduction of electric field measurements means that our simulation framework can be used as a predictive tool, even for rovers and satellites that deal with small cyclones known as (dust devils) on the surface of Mars.”