The flow of air is a subject studied by the discipline of fluid dynamics and, in particular, by aerodynamics. Isaac Newton was the first scientist to be occupied with what is currently known as aerodynamics after developing the theory of air resistance. Since then, huge steps have been made to understand the forces and moment loads acting on an object as a result of airflow. Those concepts are applicable in civil engineering as the air forces are taken into consideration when designing a structure. Furthermore, aerodynamics has been widely used in the automotive and transportation industry to produce efficient vehicles and aircrafts.
A new study, presented in November 2020 at the annual (virtual) meeting of the American Physical Society’s Division of Fluid Dynamics, assesses the airflow that develops in urban environments. The rise of tall buildings, skyscrapers and vast facilities affect the natural movement of the air and the subsequent air pressures.
To model the airflows in cities, a phenomenon known as building wakes must be quantified. Wakes refer to areas behind a stable mass (buildings in this case) where airflow is disturbed and recirculates due to its viscosity. Understanding how this phenomenon works can aid in predicting the airflow gradients, the velocity and the air pressures in these regions.
To investigate the structures' wake, the research team conducted experimental tests in a wind tunnel for a single building and for a group of buildings. Scientists changed a lot of parameters during the tests including the distance between the structures and their height.
The results suggest that the airflow downstream differs for a group of structures and for a single structure but this change was observed within a certain distance. Beyond that distance, the wake patterns were similar. The airflow was also found to be highly impacted by the direction of the wind which is a result of asymmetry in building patterns.
The team also studied the building wakes in-situ. The researchers launched aerial vehicles equipped with special sensors that measured the disturbed airflow characteristics around buildings and incorporated the finding in numerical models.
They found that current passive ventilation systems are inefficient since they operate in a cool air-warm air exchange process during the night which is characterized as "unbalanced".
Scientists suggest that all buildings must be properly ventilated for the ease and health of people. Inadequate ventilation can result in significant problems including the spread of airborne viruses like the COVID-19.
The study aims at improving computer modeling and predicting wind patterns so it can provide valuable information for future applications including new tall structures and air transportation (drones, flying systems, etc.).
An interesting video on the impact of building on airflow can be found below.
Source: AmericanPhysicalSociety, Simscale
