Effect of surcharge on gully-manhole flow

Abstract

In an urban drainage system, surface system and buried system are connected through several linking elements like gullies and manholes. To model an urban flood through a 1D or 2D routing model, proper representation of these linking elements is mandatory. This paper focuses on the effects on inline manhole head loss coefficient and gully flow due to change in manhole surcharges to get knowledge of their characteristics, flow patterns and influence in the overall flow. The solver interFoam with VOF capability under open source CFD toolbox OpenFOAM® is used for the numerical simulations. The CFD model created is a real scale model following the experimental setup installed at the University of Coimbra. The CFD model results were compared with discharge and water depth data at the manhole and velocity data at the gully, measured from the physical model. The manhole head loss coefficient was found very high at low surcharge level and reaching a constant value of 0.3 for higher surcharge levels. The gully flow was found to follow typical orifice flow equation with different discharge coefficients for different water depth conditions of the manhole. Three different surcharged zones were identified at the manhole on which discharge coefficients are dependent. The shear stress pattern at the manhole floor is also found varying due to surcharge depth as well as the gully flow. The variation showed distinctive configuration at different surcharge zones.

Numerical Research of Flows into Gullies with Different Outlet Locations

“…The Pressure-Implicit with Splitting of Operators (PISO) procedure proposed by [22] is used for pressure velocity coupling in transient calculations with 3 loops. We used the same discretization schemes employed in previous works on gullies tested with positive outcome [10,13] as well as we used turbulence models with the best accuracy [2].…”

“…In the past decade, there has been an increasing use of dual-drainage models, linking storm water pipe flow (the buried system or minor system) to the overland flow (the major system). Models of the minor system increasingly allow for detailed modelling of the network through representing all manholes, combined sewer overflows, outlet devices, control facilities, among others, usually by defining discharge coefficients [1,2]. On the other hand, some particular structures and devices, such as gullies and manholes, have been analyzed using either experimental investigation [3,4] or computational fluid dynamics (CFD) [2] in order to understand flows and search for parameters that characterize such flows.…”

“…Models of the minor system increasingly allow for detailed modelling of the network through representing all manholes, combined sewer overflows, outlet devices, control facilities, among others, usually by defining discharge coefficients [1,2]. On the other hand, some particular structures and devices, such as gullies and manholes, have been analyzed using either experimental investigation [3,4] or computational fluid dynamics (CFD) [2] in order to understand flows and search for parameters that characterize such flows. The understanding of the underlying physics and the capability to model these physical phenomena allowing to adequately predict the flow field is of paramount importance to perform numerical environmental studies [5].…”

“…Factors such as the local geometry and the location of the gully outlet are also known to influence the flow. CFD is becoming increasingly used as part of simulation schemes for hydraulic structures in urban drainage systems [2,[11][12][13].…”

“…In particular, Beg et al [2] tested different turbulence models and compared them with experimental measurements, concluding that Shear Stress Transport (SST) k-ω and Renormalization Group (RNG) kturbulence models reached best accuracy. Also Lopes et al [13] presented simulations of a specific gully using SSTk-ω with a high accuracy.…”