Our researchers have been busy carrying out experiments at test buildings, in the wind tunnel at Surrey and using the Cambridge water tank. Here's a snapshot of some of our latest findings. 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.
Setting up our new Cambridge test site:
Shiwei and the test team are well underway with experiments and monitoring at our second test site, which is at the University of Cambridge architecture department. It's an interesting site for us because, being next to both a busy main road and also a large expanse of green space with a river, it will help us to better understand the impact of green and blue space on pollution flows. Working with Cambridge City Council we've set up MAGIC monitors and temperature loggers around the city and we've also put MAGIC monitors, wall temperature monitors, two ultrasonic anenometers and a temperature array in the room itself. As well as ongoing monitoring we are also conducting short-term, controlled experiments to explore the impact of different window opening set-ups on natural ventilation and comfort in the room. The photo opposite shows the room with our monitoring equipment carefully positioned.
Figure shows the water bath experiment as viewed from the side
Using the water tank to understand ventilation flows:
Megan and her team have begun experiments investigating the effect of temperature differences on cross-ventilation. The experiments are performed in a large flume, with a cross-sectional area of 2 m x 1 m. Into the flume is placed a model room, which is a 0.5 m cube. Before the start of an experiment, the water inside the model room is heated and dyed. The flume is switched on, to provide a flow past the model room, modelling the effect of wind. Two windows are opened on opposite walls of the model room, one at the front, facing the wind, and one at the back. For this experiment, the flow velocity was 2.5 cm/s and the temperature difference was 1 degree C. The dyed, warm fluid inside the room (red) is flushed out by the wind, cooling the lower layer of the room, up to the top of the windows. At late times, there is a two-layer stratification in the room - a warm upper layer and a cool lower layer.
Experiments performed by Megan Davies Wykes and Elkhansaa Chahour.
Wind tunnel work:
This is a bird’s eye view of wind tunnel model of the London Road test site. Will's latest addition is the accurate roof features - the devil is in the detail! In these experiments, the wind tunnel mean flow was from left to right. The light beams of the laser Doppler anemometer were deflected with a mirror to measure wind velocity at roof height and below. Surface pressure was measured at the test room windows and Will found that the roofs had some effect on the pressure difference between the road and the courtyard sides.