Capita Symonds Heralds Flood Risk Revolution

Posted: Tuesday 7th June 2011

Capita Symonds’ Flood and Water Risk management team have been using a revolutionary Computational Fluid Dynamics (CFD) system on a project to protect the town of Hereford from severe flooding.

CFD is one of the branches of fluid mechanics that uses numerical methods and algorithms to solve and analyse problems that involve fluid flows. Computers are used to perform the millions of calculations required to simulate the interaction of fluids and gases within complex structures used in engineering.

The initial design for the Hereford Flood Alleviation Scheme (FAS) was constrained by the local topography, the River Wye’s outfall flood levels and the visual impact on the environment. An essential part of the FAS was the design of a bespoke Energy Dissipation Chamber (EDC), to minimise scour at the outfall structure, caused by the rapid decent of flows onto the River Wye floodplain.

The EDC design was based upon the proportions of the United States Bureau of Reclamation Type II stilling basin and the efficiency of the design was confirmed by hydraulic calculations following recognised design guides. However, since the specifics of the EDC were outside of UK standard practice and additional confidence in the operation of the structure was required.

A 3D computational model of the structure was constructed by the Capita Symonds team using ANSYS’ FLUENT CFD software. The model was used to appraise the hydraulic performance of the EDC for various flood discharges and outfall water levels, providing detailed information on flow velocity magnitude, wall pressure and air entrainment. The added insight and understanding provided by the CFD outputs gave confidence in the design proposals, avoiding added cost through conservative oversizing, whilst reducing risk.

This project is but one of the many application areas benefiting from CFD analysis. CFD is increasingly being used by various other industries - including power generation, chemical engineering, construction, aerospace, automotive and process - either to reduce manufacturing design cycles or to provide an insight into existing technologies so that they may be analysed and improved. For example,Capita Symonds’ Flood Risk and Water Management team used CFD in the fire safety design and optimisation of the tunnel ventilation systems on the £100m M25 Bell Common Tunnel project. They have also analysed heating ventilation and air conditioning systems within building using CFD to determine optimum air flow rates and thermal comfort levels.

Matthew Roberts, Capita Symonds, explains: “As a design tool, CFD presently sits besides experimental analysis as numerical methods, which govern the solutions in a CFD problem, rely on several modelling assumptions that need to be validated to a satisfactory level. However, CFD offers itself as a powerful design tool and even more so in the future because:

▪ When a CFD model can be established yielding accurate results on one particular design, then the model can be used as a tool of prediction for that design under many different operating conditions.

▪ Dangerous or expensive trial and error experiments can be simulated and design parameters observed prior to any physical prototype being constructed;

▪ The numerical schemes and physical models that are the building blocks of CFD are continually improving; and computers are becoming even more powerful and less expensive, thus allowing larger CFD simulations to be calculated, or more detailed simulations of present CFD problems.”

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