Envisaging a world with greener cities.

Linking inside and outside in Fluidity

The team developing Fluidity at Imperial have now linked indoors and outdoors - creating a full two-way coupling in the Fluidity model.

An extensive comparison (velocity profile, reynolds stresses concentration and pressure coefficient) between the wind tunnel experiment and Fluidity simulations have also been successfully completed.

The thermal processes occurring in the urban environment are currently being integrated into the model. To do this, a turbulent inlet temperature boundary condition was developed to simulate stable, unstable and neutral atmospheric boundary layers. The video below shows the velocity magnitude field and the temperature field for an unstable boundary layer.

research updates: Modelling

Figure shows indoor thermal conditions for weekdays during July-August period in 2017 under the best window control scenario during working hours


Read previous updates in our MAGIC circular, produced quarterly:

Modelling Emissions

The traffic model is also progressing. Huw is adding the physics required for urban dispersion modelling into the Fluidity model. For example, coupling the traffic model with an instantaneous vehicle emissions model, the NOx chemistry model and also the modelling of trees.

On the left, the top video is a bird’s eye view of the dispersion of vehicle emissions at a crossroads. The vehicles are shown in green while the emissions from each traffic lane is shown as a different colour. The red emissions correspond to the bus lane.

The bottom video shows the same crossroad from a street level viewpoint. The pink cloud here represents the emissions from the traffic on the road crossing from left to right. The buses can be seen to entrain the emissions from this road, carrying the pollutants along the street. 

Modelling the potential of natural ventilation to cool on the hottest days:

On further analysing the data from the LSBU test room and running simulations in the Energyplus model, Jiyun found that a combination of cross- and stack-ventilation can keep the room comfortable for inhabitants 92% of working hours. On very hot days, a combination of nighttime cooling, daytime natural ventilation and blinds shading are effective to make the office room thermally comfortable. 

At the heart of MAGIC are a number of computer models - including Fluidity, a Reduced Order Model and Energyplus. We have a dedicated team of modellers building and refining the models' capabilities. Here's a snapshot of some of their latest work.  A full summary of  our  research can be found in the paper recently published paper in Building Research and Information: Natural ventilation in cities: the implications of fluid mechanics.