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Developing the pool CFD model

24 November 2021

What is Computational Fluid Dynamics (CFD)?

Computational Fluid Dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyse and solve problems that involve fluid flows.

What does that mean?

Similar to a wind tunnel test on a concept car or wind modelling how architecture affects a public space, CFD acts as a virtual fluid dynamics simulator.

How does CFD benefit swimming pool engineering?

The objective of CFD in swimming pools is to assess the effectiveness of the pool water distribution in the pool tank.  This is done by simulating a pool dye test (which is required by BS EN 15288) prior to construction,

 

Our journey so far…

The Devin journey with CFD started in 2020 with:

  • research and procurement of the Autodesk generic CFD software
  • establishing a strong in house CFD team and then
  • three weeks of training to cover all of the basic aspects of the software, geometry creation, materials, boundary conditions, meshing, turbulence and solving simulations.

A well-designed swimming pool will typically be fully coloured with dye after a 15 minute period. As valuable as a dye test is, we only witness it from the pool surround and have a limited view of what actually happens beneath the surface. It’s difficult to know if we are getting good distribution of water to the bottom of the pool.  CFD is a great tool to help design teams understand more precisely, what is happening. 

CFD is not an exact science; it demands compromise and assumption, like any engineering model and achieving the correct balance can often require an element of trial and error.  From a very early stage it was clear that our Revit models could not be used for CFD purposes.  A Stage 4 Revit pool tank model contains too much detail for the software to handle and conversely insufficient detail where we really need it! The pool tank geometry had to be re-modelled from scratch and required a transition through a third piece of software to further refine the geometry and create the fluid volume.

After our pool geometry was loaded into CFD, we were able to starting assigning suitable parameters, boundary conditions and materials. We generated a working pool tank model, with a steady state flow simulation – we mapped the velocities.  It was useful data, but a velocity map doesn’t represent the real flow distribution and we needed to find a way to show both dye and water in the model whilst being able to differentiate between the two.

To achieve this, we brought another parameter into play, time. Whilst our steady state simulation presented a snapshot of the pool under normal running conditions, it didn’t show how things would change from one minute to the next. This is where we moved to a transient simulation. This involved simulating the pool over a 20 minute period. At the start of this period, the pool would contain only water, but then we’d immediately introduce dye at each of the inlets, allowing us to see the spread of dye into the water over time.  Progress!

The story continues January 2022 in Part II – Verifying the pool CFD model

If you’d like to know more about how CFD can benefit your next swimming pool project, email Keely at kwilkinson@devin-consulting.com or give us a call on 0191 2581653.

Section through a 25m pool tank showing higher velocity water local to the inlets.

 

View through an inlet and base outlet at the deep end of the 25m pool showing water velocities and directions.