Previous research into surcharged manholes has highlighted the existence of a threshold surcharge level that separates two distinctly-different hydraulic regimes. Sharp changes in manhole energy loss and solute transport characteristics occur when the surcharge depth passes through the threshold level. With respect to solute transport, two scale-independent cumulative residence time distributions (CRTDs) have been identified, corresponding to the below-threshold and above-threshold hydraulic regimes. However, previous studies focused on large diameter manholes, in which the manhole diameter (Φm) was at least 4.4 times greater than the pipe diameter (Φp). This paper utilizes a validated computational fluid dynamics (CFD) modeling approach to explore the hydraulic behavior and mixing processes in small-diameter surcharged manholes (1.5<Φm/Φp<4.4). It is shown that the hydraulic threshold does not exist in the small diameter manholes; instead, the flow field is characterized by short-circuiting throughout the full range of surcharge depths. Data generated at low surcharge levels suggest that the mixing effects in the below-threshold region are not independent of surcharge level, as had previously been suggested. The absence of the threshold in small-diameter manholes is explained with reference to jet theory. Several previous studies that have characterized mixing and/or energy losses in surcharged manholes are revisited, allowing findings to be generalized across a broader range of manhole configurations, including effects attributable to benching and change in outlet angle.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)