Fund research into ventilation and airflow on buses

Buses are a vital element of public transport and in normal times are relied on by many to travel daily to work, shops and leisure activities. We have all sat on buses with the windows steamed up or running with condensation. The ventilation on both single and double deckers appears to be a combination of forced air and the opening of flaps above some windows. A considerable body of research is published on airflow in transporters used to carry farm livestock. It shows that the air flows from the back of the transporter to the front when it is moving and that forced air is needed when the transporter is stopped. The only published research I can find on buses is an Indian study from 2007 (see an abstract below). It also found that the air in a moving bus was from the back to the front. We need to understand whether ventilation on buses is adequate to dissipate infectious virus particles or whether the existing systems place passengers and drivers at increased risk of contracting respiratory infections such as COVID-19.

S ̄adhan ̄aVol. 32, Part 4, August 2007, pp. 347–363. © Printed in IndiaAir flow through a non-airconditioned bus with openwindowsS R KALE1∗, S V VEERAVALLI2, H D PUNEKAR3andM M YELMULE1#1Department of Mechanical Engineering, Indian Institute Technology Delhi,New Delhi 110 0162Department of Applied Mechanics, Indian Institute Technology Delhi,New Delhi 110 0163Fluent India Pvt. Ltd., Pune 411 057e-mail: srk@mech.iitd.ernet.inAbstract.Open window buses without air-conditioning are a major mode of urbanand inter-city transport in most countries. High occupancy combined with hot andhumid conditions makes travel in these buses quite uncomfortable. In this study airflow through a bus has been studied that could be the basis for low cost and eco-friendly methods of increasing passenger comfort and possibly reduce drag. The aerodynamics of such a road vehicle has not been studied as previous investigationshave been confined to vehicles with closed windows that present a smooth exteriorto air flow. Using a 1:25 scaled Perspex model of an urban bus in Delhi, flowvisualization was performed in a water channel. The Reynolds numbers were one-tenth of a real bus moving at 10 m/s. Smoke and tuft visualizations were alsoperformed on an urban bus at 40 km/h. Numerical simulations were performed atthe actual Reynolds number. Even though there were Reynolds number differences,the broad features were similar. Air enters the bus from the rear windows, moves tothe front (relative to the bus) and exits from the front windows. Inside air velocityrelative to the bus is about one-tenth of the free-stream velocity. The flow is highlythree-dimensional and unsteady.Keywords.Open window buses; urban transport; flow visualization; numerical

Firstly we need publicly funded research to understand whether ventilation on buses is adequate to dissipate infectious virus particles from buses or whether the existing systems place passengers and drivers at increased risk of contracting respiratory infections such as COVID-19. Secondly we need to know what modifications can be made to buses to improve their ventilation. Ideally these modifictions should be quick and easy to implement and inexpensive.

Currently there are suggestions in the media that buses drivers are at a high risk of contracting COVID-19 and many bus drivers have died. Throughout the country many depend on buses to commute to and from work but concern about exposure to COVID-19 threatens their mobility. At present, suggestions to reduce the risk of contracting COVID-19 infection while travelling on buses appears to be (1) greatly reduce the number of passengers travelling (uneconomic and excessively polluting) and (2) wear face masks (unlikely to be effective especially on longer journeys).