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Flushing out design: DEM essential in toilet product development

Let me say right off that toilet talk is not a common topic for a Rocky blog. But ultimately, this is about using simulation to save water.

Even toilets need to be optimized to meet diverse (and sometimes customized) consumer demand and regulatory water-usage requirements. Compared to the alternative, I expect that you would prefer to apply engineering simulation methodologies to this and other applications, because it solves a lot of problems.

At Roca, a worldwide leader in bathroom plumbing products, our charge is to develop new ways to innovate and adapt product designs. This can be challenging, since many of our toilets, sinks, faucets, bathtubs and shower columns are time-tested designs that have maintained their basic configuration for decades. Roca’s toilet product developers rely on engineering simulation to quickly and cost-effectively identify fluid-flow complexities, especially as we address water-conservation mandates. Adding coupled discrete element modeling (DEM) to the mix means we can identify accurate particle behavior without flushing some of our profits down the drain.

In the past, Roca conducted liquid−solid particle investigation efforts by using physical experiments. With the latest release of Rocky DEM, which offers the ability to simulate realistic solid/shell/fiber/rigid/flexible matter, Roca realized that conducting virtual particle analysis could reduce the need for building prototypes, saving the company time and costs.

VOF Multiphase Model for toilet design
VOF Multiphase Model

Eulerian Multiphase Model for toilet design
Eulerian Multiphase Model

Using Rocky DEM to optimize toilet design for low-water usage

European toilet design uses wash-down technology, in which water is flushed very quickly into the bowl via a rimless design, pushing waste out. But the catalyst project for using Rocky DEM was fine-tuning a low-water-consumption siphonic toilet design, a product typically used in the United States and Asia. This mechanism creates a vacuum effect in the bowl’s trapway as water is released, so waste gets pulled out by water.

We had already optimized the wash-down toilet design for low-water usage. But very different physics are involved in pushing water versus pulling it. Our objective was to improve the siphonic toilet design to reach the same performance level as the wash-down model: meeting minimum water-consumption standards and delivering maximum drainage power.

To ensure simulation accuracy, we constructed a real siphonic toilet to use as a calibration model, measuring physical parameters such as water pressure/distribution in the toilet’s rim and jets, reaction times and refill volumes. Understanding how water flows through a toilet is extremely complicated, because every single parameter affects the final performance.

The engineering team leveraged the proven power of Ansys Fluent CFD software and engaged the Rocky DEM technical team to incorporate particle analysis as a first-trial run. We chose Rocky for its seamless Fluent coupling, its ability to model a variety of particles — high-solids concentrations, non-spherical particles, flexible particles, adhesive/cohesive materials — as well its facility in predicting accurate particle−particle heat transfer and particle−size distribution.

Roca’s Rocky DEM toilet model called for spherical (above) and cylindrical flexible-fiber (below) particles.

Now, for the first time, the Roca engineering team can validate simulations using both discrete particle shapes with and without spherical particles. We conducted two case-study simulation sets consisting of two-fluid phases (water–air), solid particle phase, Eulerian multi-phase and gravity only. Case 1 depicted spherical solid rigid particles, while case 2 incorporated cylindrical flexible fiber particles with 18 division elements that exhibited joint linear−elastic behavior.

An important part of creating a reliable DEM simulation is using models that accurately reflect the material’s behavior. The engineering team set virtual particle density, shape and other properties to represent the same mass and volume used in experiments. Rocky DEM enabled us to control both particle−particle friction and particle−equipment adhesion as well as to adjust fiber flexibility to match real data.

Coupled CFD−Rocky DEM model case 1 (above) shows how flushed water pulls spherical solid, rigid particles out of the bowl. Case 2 (below) shows flexible-fiber particles.

The results of physical tests and simulations were strikingly similar, giving us confidence that we could rely on coupled Ansys−Rocky software to reduce physical testing.

Each simulation required a week to prepare, run and analyze the results. If the team had constructed physical mockups of these different geometries, each one would require three weeks. By using Ansys CFD simulation software, Roca’s engineers significantly reduced the number of prototypes for new products (and resultant time and costs), and we expect even greater savings by adding Rocky DEM to the simulation mix.

Vicens Font

Advanced Toilet Technology Manager at Roca

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