Hydraulic engineers prefer scale models to CFD
04 April 2013
Computational fluid dynamics (CFD) modelling has been around since the early sixties when the first work using computers to model fluid flow was performed at Los Alamos National Labs, by the T3 group.
Computers are now routinely used to perform the calculations required to simulate the interaction of liquids and gases with surfaces defined by boundary conditions. However, even though these computations are now very robust and accessible, there are still circumstances where testing the real thing is both faster and, ultimately, more accurate.
UK-based HR Wallingford undertakes specialist hydraulic design in civil engineering projects and provides associated modelling services in support of the development of major infrastructure projects for shipping ports, harbours and marine terminals. The company’s work also includes studies destined to improve the infrastructure in river & coastal engineering schemes where optimisation of intake and outfall pumping stations is required.
Physical scale modelling techniques are used in conjunction with, or as an alternative to, CFD in order to investigate the performance of the associated hydraulic structures, and to validate or optimise the designs of these large civil works. It was in the context of this highly specialised activity that Rapitypes was recently invited to assist with additional prototyping support.
In these examples, a one tenth scale physical model is being used to investigate the hydraulic performance of a cooling water intake to a pumping station for a major new power plant project. The model was used to identify the potential for vortex action and swirling flows that could cause operational problems at the pumping facility.
Rapitypes supplied accurately shaped representations of the pump intakes using transparent materials that allowed complex flow patterns within to be studied and filmed. The company’s expertise in toolmaking and prototyping was brought to bear in providing a number of identical, yet closely toleranced scale models, and a one-off machined acrylic bifurcated channel (representing a tunnel junction system associated with a hydropower project in Pakistan) for use at HR Wallingford’s physical modelling facility in Howbery Park.
The models were used to identify the required design changes to the structures that were necessary to ensure optimal hydraulic performance. CFD and computer aided modelling analysis have important roles to play in modern engineering design, but sometimes the physical model is the better proposition and this was clearly the case in the studies carried out at Howbery Park.
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