Urban Planning

In designing and constructing new buildings, roadways, public transportation systems and broad city management projects particularly in urban areas where interaction with existing structures, inhabitants and overall environment are essential, careful consideration must be given to computing the effects of flow and its impact. Adding immensely to the difficulty of such a task and the extremely complex nature of computing flows around buildings and urban street canyons is the re-circulation and reattachment of a flow. Vorticity Confinement (VC) is a powerful tool to address all the very complex issues and efficiently model airflow around buildings. Simulations performed to evaluate are as follows:

1. Pollution dispersion

The complex nature of airborne pollutant transport in urban environment with recirculation zones and wakes is easily computed in the VC model. Studies and experience indicate the transport and dispersion of pollutants is guided by the presence of buildings. The development of a wake behind the building typically spreads the pollutant to a larger zone than in a clear area. Also, dead zones play a dominant role, which are prone to accumulate the pollutant and create a health hazard. The extent of transport depends on the free stream wind speed and direction. It is very necessary to compute the transport for several test cases to accurately determine the propagation and dispersion. Using VC, the computations are fairly simple due to the usage of a Cartesian grid to immerse bodies of any irregular shape providing the ability to compute for many variables.

2. Pressure forces on buildings

The flow over array of buildings is an example of flow with separation around an object. In a closely spaced urban layout, the wakes are disturbed and change the regime to wake interference flow, creating large eddies in the lee side of the building. The air flow in and around the buildings can be computed by simply immersing the geometry of the building in the Cartesian grid. Thus, VC offers more flexibility to predict air flow for a variety of building designs and modifications. Understanding wake dynamics predominantly determines the distribution of forces on the object. This is important to study the effects of wakes on the structure of the building. The numerical predictions of wind induced pressure on the walls of the building are provided.

3. Air Flow comfort assessment

The construction of a building changes the wind climate of the area to a large extent. In an urban layout, the buildings are the major sources for the formation of regions of accelerated flow at the ground level, which creates discomfort and sometimes danger to pedestrians. VC allows to effortlessly prototype and alter the design of the building. This is provided through the immersed boundary model, reducing development time and costs. VC delivers wind comfort assessment studies performed accurately using a modeling technique with no inherent complexity. Effects of the building on the outdoor environment are provided as output, which will be helpful in determining an optimized position for walkways, benches, entrances, pedestrian areas, etc.

4. Smoke control

It is far too expensive to carry out full-scale burning tests to study a fire in an urban environment. Also, affordable small scale physical simulations do not have the range of vortical scales necessary for realistic simulations. An obvious alternative is to use the VC based computational model to better understand the smoke transport and dispersion. VC seems to be the only Eulerian computational method that has the range of vortical scales necessary for realistic turbulent simulations. The VC output data can enable the architects and engineers to visualize and track the spread of the smoke in and along the emergency paths. This in turn will lead to a better emergency response judgment.

Fire and smoke distribution data for halls with high seating capacity is also an output of the model and can be used to assist designers to plan an optimized smoke evacuation path to determine the least amount of poisonous gases flowing through the building. Such studies are also important for subway trains, train stations, airports, business complexes and other public places. Natural ventilation openings have to be placed at optimized locations for better smoke management to ensure the people’s safety during evacuation.

5. Ventilation

Achieving good indoor air quality in large residential and commercial buildings continues to be a top priority for designers. Passive cooling creates indoor airflow that minimizes the need for a conventional air conditioning system and plays a predominant role in reducing a building’s energy costs. This kind of natural ventilation is obtained by designing in chimney effects and other flow controls by the architect. Natural ventilation is driven by buoyancy pressure (stack effect) and by wind pressures. Output from VC can be used to assess indoor airflow for effective natural ventilation design regardless of how complex the building/interior geometry is. Ventilation can control the indoor air quality by both diluting the indoor air with less contaminated outdoor air and removing the indoor contaminants with the exhaust air, speeding up the dilution process. Supplying outdoor air to an enclosed space and removing stale air from this space is necessary for smoke/contaminant management.

As with all flow applications modeled with VC, thousands of complex prototypes must be (and can be) computed in a fraction of the time not only surpassing the more conventional models and testing protocol.