科研之友
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摘要
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 () was at least 4.4times greater than the pipe diameter (). This paper utilizes a validated computational fluid dynamics (CFD) modeling approach to explore the hydraulic behavior and mixing processes in small-diameter surcharged manholes (). 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.
