Experts use wind tunnel to assess COVID-19 transmission risk during exercise

Working in the 10x5 wind tunnel at Imperial College London’s Department of Aeronautics, the researchers want to obtain detailed data on concentrations of viral particles generated by individuals exercising outdoors, whether walking, jogging, running or cycling.

This data will provide Public Health England and Government committees with a quantified tool to help assess the infection risks, as well as practical strategies to minimise infection rates.

Transmission risk

Respiratory infections like COVID-19 can be transmitted via an infected person’s exhaled breath particles. 

During the wind tunnel experiments, participants exercise on fixed equipment like exercise bikes and treadmills under conditions which accurately simulate the relative motion through the air of an exercising person.

Researchers then measure particles of carbon dioxide (CO2) from exhaled breath within the air currents behind the person exercising. Small particles present a risk in that they remain airborne as an aerosol, with the potential to be inhaled by someone nearby. Larger particles are also a risk, since they are strongly influenced by gravity and tend to settle on surfaces where they can leave a residue of the virus.

CO2 is used as a surrogate for the virus-carrying aerosol, and is measured using new sampling probes, known as ‘AirSniffers'.

Co-leads on the project Dr George Papadakis and Professor Denis Doorly from the Department of Aeronautics, said: “Our wind tunnel offers a unique way to test something that’s a big question during the coronavirus pandemic: how does exercise affect airborne transmission of the virus?”

Ali Yousefian, founder and director of AirPortal Ltd., which manufactures the AirSniffers, said: “We provided the technology for the team to obtain first-time quantitative data on the spread of droplets exhaled under normal and exercise conditions in free air.

"As it currently stands, there are no available studies which analyse the effects of aerodynamics when it comes to activities which involve motion and exercise. This lack of experimentality and reliable quantitative data has been the overarching motivation for this project.”

Dr James Hull, a Consultant Respiratory Physician at Royal Brompton Hospital who is working with the Aeronautics team on the project said: “The work could  inform guidance on exercise precautions, which is vital in helping us to ensure that people remain physically active and do so in the safest way possible.”

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Above: Video of Dr Kevin Gouder on an exercise bike in the 10 x 5 Wind Tunnel. AirSniffers are placed around him to detect the particle concentrations.

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Above: This video shows an example of a droplet cloud in the wake of a manikin simulator.

Manikins 

Alongside experiments with human test subjects, the team are performing experiments using manikins fitted with simulated breathing capability. The manikins allow for measurement techniques that are normally restricted with human subjects due to safety reasons. Consequently, the techniques can be widened to include strong laser sheet illumination and a greater range of tracers.

The experimental measurements are supported by a programme of numerical simulation of the same flows using Computational Fluid Dynamics (CFD), in which the Department has a great deal of expertise. The CFD simulations are detailed and time accurate, using large eddy simulations of the turbulent flow, which allow for full representation of the thermodynamics of aerosol evaporation and droplet particle tracking.

As a result, the team can measure a much more detailed mapping of concentration and droplet size distributions and statistics of means and extremes. This extends to the region around the subject’s head and body and in the wake as far downstream as necessary.

Professor Nick Cheshire, Head of Vascular Surgery at Royal Brompton & Harefield NHS Foundation Trust as well as Director of AirPortal Ltd. also believes the work "could inform public health policy and help define best practice to avoid the spread of COVID-19."

More information about the project can be found on the 10x5 wind tunnel's research page.