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Comparison of Flow Hydraulics in Different Manhole Types

Author(s): Md Nazmul Azim Beg, Rita F. Carvalho, Jorge Leandro

Linked Author(s): Maria Rita L. M. F. Carvalho

Keywords: Urban drainage, manholes, CFD, OpenFOAM�, head loss coefficient.

Abstract: Manhole is a very common and important element in an urban drainage system. The complex flow pattern in a manhole may include the effects of retardation, acceleration and rotation, creating energy losses in the network. Different types of manhole are seen in various countries due to different design criteria. Three different manhole types were modelled in this study to analyze the hydraulic properties of them. Type C has a guided channel at the bottom, while Type A and Type B do not. Type A also has a seal underneath the inflow-outflow pipe; but in Type B, the invert level of the inflow pipe is at the same level of the manhole floor. Analysis were done numerically using volume of fluid (VOF) model with open source CFD modelling tools OpenFOAM�. The numerical results were verified by mesh independency test using Richardson extrapolation method. Results showed that the flow structures and head loss coefficients vary in different manholes. All three manholes showed higher head loss coefficients at low surcharge conditions. Out of the three manhole types, Type A and B showed higher head loss coefficient than Type C. The threshold surcharge levels at Type A and B were found approximately 20% of the manhole diameter. However, for Type C, the surcharge threshold level was found higher. The study may provide essential information to calculate the head losses of these types of manhole in an urban drainage network model


Year: 2017

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