It is now recognised that COVID-19 is spread by respiratory aerosols and droplets which can result in airborne transmission [1] [2]. As users of CFD tools, many of us have considered or been asked what simulations we can do to support the fight against the virus and protect people against infection. One of the benefits of CFD is that it makes visible what we would otherwise not see, but it is also vital to know how well the simulations capture what is important. Validation is challenging, boundary conditions may not be clear, and what about factors like the transient effects of breathing and the motion of people? Further important questions exist around how to treat turbulence, which simplifying assumptions to use, and how all this relates to viral load.