On the Characteristics of Velocities Fields in the Vicinity of Manhole Inlet Grates During Flood Events

Abstract

The accurate characterization of flow from urban surfaces to sewer/stormwater systems is important for urban drainage design and flood modeling/risk identification. However, the geometrical complexity and large variety of drainage structures (linking elements) available makes model calibration and verification difficult. In this study an extensive comparison between experimentally measured and numerically modeled flow characteristics in the vicinity of ten different designs of manhole grate was performed under drainage flow in subcritical conditions. Using a 2‐D surface PIV (sPIV) system the work presents the first detailed characterization of velocity fields around these linking elements. In addition, it provides the first detailed verification of the ability of a 2‐D numerical model to describe both velocity fields and drainage flows. The overall comparison shows a close relationship between numerical and the experimental results with some higher inflows in the experimental results as a consequence of a localized transition from weir to orifice condition near the void areas of the grates. It was also noted that velocity differences decreased further from the manhole, due mainly to the more directional flow. Overall the work demonstrates the potential for further use of 2‐D numerical models to describe flow conditions at linking elements, either directly within modeling simulations or indirectly via the characterization of energy loss coefficients.

Technical note: Laboratory modelling of urban flooding: strengths and challenges of distorted scale models

“…While the motivations for using a large distortion ratio between the horizontal and vertical scale factors are not arguable (fit the model within a limited laboratory space, improve the accuracy of water depth measurement and maintain a sufficiently high Reynolds number), the assumption of having no artefacts in experimental observations performed on a strongly distorted model may legitimately be questioned. Among other aspects, the complex three-dimensional flow structures observed in individual crossroads (Mignot et al, 2008(Mignot et al, , 2013Rivière et al, 2011Rivière et al, , 2014 suggest that "shrinking" the model vertically is likely to alter these flow structures and hence also impair the representation of flow partition in-between the streets. The influence of strong distortion in laboratory-scale models was investigated for some specific applications, such as in coastal engineering (Ranieri, 2007;Sharp and Khader, 1984), but it has not been analysed to date in the context of laboratory models of urban flooding.…”

Hydraulic, wash-off and sediment transport experiments in a full-scale urban drainage physical model

“…However, this leads to an increase in the input variables needed to accurately determine and make a precise representation of the surface flow needed. Gully pot modelling 17,18 and sewer transport modelling 19,20 , as well as interactions between surface and drainage systems [21][22][23][24] , are also key in order to provide an integrated solution to runoff TSS mobilization.…”

“…Finally, the resulted velocity distributions that are provided correspond to the surface flow velocity and not to the depth-average velocities. Some authors use a flow velocity correction factor from 0.6 to 1 based on the log-law velocity profile 24,42 , and in Naves et al 27 the classical value of 0.85 was applied. However, due to the very shallow flow conditions, this assumption is not expected to add significant uncertainties.…”

SPH Simulation of Interior and Exterior Flow Field Characteristics of Porous Media

“…The traditional velocity measurement method is difficult to be used in permeable buildings. Particle image velocimetry (PIV) and particle tracking velocimetry (PTV) are other robust experimental techniques to solve this problem [28][29][30][31][32][33][34][35]. In this study, the Lagrangian particle tracking method is used to measure the velocity distribution along the water depth at different positions.…”