How does Covid-19 spread through the air?

The skills of LEGI (CNRS, Grenoble INP, UGA) in fluid mechanics are used to understand the aerial propagation of Covid-19

How does Covid-19 spread through the air?

One of the suspected modes of transmission of Covid19 is by means of air. What happens when your neighbour sneezes, coughs or simply breathes near you?

Micro droplets containing the virus can be ejected and held in suspension and possibly inhaled by others.

In order to find out for sure, LEGI researchers, at the request of TIMC colleagues (CNRS, CHU Grenoble Alpes, Grenoble INP, UGA, VetAgro Sup), have been looking into this question.

"Assessing the risks associated with this mode of transmission and the effectiveness of protective devices requires considering many configurations," explains Guillaume Balarac, lecturer at Grenoble INP - Ense³ and researcher at LEGI. Numerical simulation can be a powerful tool for such an assessment, provided that the physical phenomena involved are reproduced as accurately as possible."

Particles and whirlpools

With their expertise in fluid mechanics in general and in the study of turbulence in particular, the researchers studied the effects of turbulence on airborne particles. Turbulence is naturally present in complex fluid flows, for example in an airflow when it meets the blades of a wind turbine, or in a water flow as it passes through a hydro turbine, in the atmosphere. And therefore, in the air we breathe!

Particularly interesting in these times of health crisis, their work, carried out in collaboration with their colleagues from CORIA, IMAG, the University of Vermont and the SAFRAN Group, has benefited from 10 million hours of computing time on the Joliot-Curie supercomputer, located on the CEA site in Paris-Saclay. Indeed, the behaviour of fluids are governed by the Navier-Stokes equation, in which turbulence is intrinsically contained. Turbulence is a phenomenon that extends over a wide range of spatial scales.

To reduce (astronomical) computational times, turbulence at the smallest spatial scales can be universally described by a simple model: vortices or turbulences are always simulated over the larger scales accessible by computation, and the smaller ones are modelled. This approach known as Large Scale Simulation (LSS) greatly reduces the computational time while maintaining a very satisfactory accuracy. 

Here, the researchers employed this method, integrated into the YALES 2 calculation code, to study the trajectory of droplets as a function of their size, external flow (ventilation), etc. The method is based on the YALES 2 calculation code. "The results, which are still being acquired and interpreted, could be used to assess the value of protective equipment such as visors. "But before that, the results will have to be interpreted by professionals in biology and virology to draw practical conclusions.