CFD of Ventilation and Exhaust Gas Dispersion in a Basement Car Park
CFD of airflow and exhaust gas dispersion in an enclosed basement car park, used to check the ventilation layout and place CO sensors.
Project brief
An enclosed basement car park gets all its fresh air from fans. The client wanted to confirm that its proposed ventilation layout would keep air moving through the whole basement and clear vehicle exhaust, and to know where the CO sensors should go.
Shirsh Technosolutions modelled the basement in ANSYS Fluent, solving the airflow and the spread of exhaust gas together.
What was at risk
In a long, irregular basement, parked cars, columns and ramps break up the flow. Air can short-circuit from a ramp straight to the nearest exhaust duct and leave corners where it hardly moves, and those corners are where exhaust gas collects. A simple air-change calculation cannot show any of this.
The client needed to see whether air reached every parking area, whether the exhaust ducts drew from the whole basement, where stagnant zones formed and where gas concentration would be highest.
Solution offered
We modelled the full basement with its ramps, columns, parked vehicles, louvres and exhaust ducts, and placed exhaust emission sources at the vehicles. The model was meshed with poly-hexcore cells and prism layers along the walls.
Ramps and louvres were set as openings, the exhaust ducts at their design flow rates, and the parking at a realistic occupancy. The flow was solved as steady RANS with the SST k-ω turbulence model, with species transport carrying the exhaust gas.
We reviewed velocity and gas concentration on planes at several occupant heights, traced the main flow paths and checked the draw at each exhaust duct. CO sensor positions were then chosen where the model showed gas gathering.
Common questions
Why solve species transport and not only the airflow? Airflow shows where the air goes. Species transport shows where the exhaust gas goes and how concentrated it becomes. Stagnant zones and sensor positions are judged on concentration.
Why check several heights? Vehicle exhaust is released low down, while people breathe at standing height. Looking at more than one height shows both where gas builds up and what someone walking through the basement is exposed to.
Challenges we overcame
Capturing airflow around parked vehicles and structural obstacles.
Predicting exhaust gas dispersion inside a long and irregular basement layout.
Evaluating airflow at multiple occupant heights.
Verifying exhaust duct effectiveness without physical testing.
Determining practical CO sensor locations using CFD instead of trial-and-error installation.
How we executed
- 1
Built a 3D model of the basement with ramps, columns, parked vehicles, louvres and exhaust ducts
- 2
Meshed with poly-hexcore cells and prism layers at the walls
- 3
Set vehicle exhaust sources, open ramps and louvres, exhaust duct flow rates and a realistic occupancy
- 4
Solved steady RANS with the SST k-ω turbulence model and species transport
- 5
Reviewed velocity and gas concentration at several occupant heights
- 6
Identified stagnant zones and checked the draw at each exhaust duct
- 7
Located CO sensors from the predicted gas distribution
Project outcome
Confirmed that airflow reaches the parking areas and identified the stagnant zones.
Showed how exhaust gases disperse and where they collect.
Checked that the exhaust ducts draw air effectively from the whole basement.
Located CO sensors from the predicted gas distribution instead of trial and error.
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