The DigIndy tunnel is an
extension of the Indianapolis combined sewer system that stores the combined
sewer overflow during heavy rain conditions. The tunnel system has several
openings in and around the city of Indianapolis. Gasses emitted from the tunnel
may create health concerns and affect the quality of life for nearby residents.
Understanding the air circulation patterns provides valuable insight into where
gases are likely to emerge from the tunnel and what steps may be taken to
mitigate gas emissions in undesirable locations. The objective of the present
work is to develop a computational fluid dynamics (CFD) model capable of
predicting the air circulation patterns in the DigIndy tunnel under dry weather
conditions. In order to inform and validate the CFD model, an experimental
campaign was designed and executed to measure weather data and air flow rates
within the DigIndy tunnel. Obtaining accurate results requires careful
consideration of key physical phenomena to include in the model, geometric
simplification strategies, mesh generation strategies, and numerical modeling
strategies. Results showed that the seasonal effect, manifest by thermally-driven
flow, plays a significant role in the air circulation patterns within the
tunnel. Furthermore, results show that tunnel alignment affects the natural air
circulation within the tunnel. Large diameter shafts, as the working and
retrieval shafts, lead to significant circulation rates in the new tunnel
alignments.