Pressure study
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Pressure study - General
The notions of overpressure and underpressure are relative and depend on the observer’s point of view.
By convention, we consider here that we are observing the building from the outside.
Unless otherwise stated, overpressure means that the pressure outside the building is higher than inside.
Wind is a balancing current between zones of different pressures.
The part of the airflow that encounters a building will be dammed up in front of it, creating a state of overpressure.
The value of this overpressure is called the “stagnation pressure”, expressed in pascal.
Pressure levels and their distribution over a building result from the interaction between the incident wind (mean velocity gradient, turbulence, etc.), the building (through its shape, dimensions, wall roughness) and the juxtaposition of immediate obstacles (or the nature of the immediate environment).
These pressure differences cause air movements through the building’s openings.
This phenomenon causes air infiltration on the windward side of the building, and air extraction from areas of low pressure.
The aim of sizing natural ventilation is to provide the best possible support for air flows generated naturally by prevailing winds:
- Calorie evacuation
- Smoke evacuation
In this context, the aim is to position air inlets and extractions according to pressure distributions; to do this, it is necessary to find zones with the same behavior(negative pressure or positive pressure) according to prevailing winds.
This favors the intended operation of the sash.
Distribution of surface pressures
When a roof is exposed to the wind, pressure builds up on the windward side and negative pressure on the leeward side.
By its very nature, a difference in air pressure between two environments tends to balance out: the negative pressure on the opposite side of the building will cause air to be drawn in from the atmosphere inside the building.
This creates an overpressure in the volume, proportional to the force of the wind, leading to the natural circulation of indoor air.
Areas of overpressure will then tend to favor air ingress.
Examples of CFD simulation applications
CFD simulation of the aerodynamic phenomena of a peloton of cyclists
CFD simulation of drag: advanced calculation to improve aerodynamics
Impact of wind on a solar power plant
Pressure loss and hydraulic resistance
Legionnaires’ disease and cooling towers
Pedestrian comfort criteria and mapping
Extreme wind study – Solar power plant
Thermal draft effect
CFD simulation: An alternative to wind tunnel testing
