Heating and cooling equipment manufacturer uses Simcenter STAR-CCM+ to save time and costs by rapidly simulating multiple pump designs

Going virtual

Pumps are the unsung heroes of many aspects of our lives. They enable our water and sewage systems, ventilation systems, cooling in energy plants and many more applications to function effectively.

Pump design engineers face multiple challenges when they aim to create new and better products. Pumps have to operate well over a range of conditions, meet government efficiency regulations and run reliably over long lifetimes with minimal downtime for repairs.

Traditional design methods have relied heavily on testing physical prototypes. This can be expensive and time consuming, with multiple cycles of design/redesign and testing for each new product. Creating a virtual prototype enables rapid investigation of multiple pump designs over a range of possible operating conditions, which not only speeds up the design process but also reduces the costs associated with physical testing. Taco Comfort Solutions (Taco) uses this approach to bring better pumps to market faster.

Design and simulation

Taco uses Simcenter STAR-CCM+® software as a virtual lab prior to creating and testing physical prototypes. Product engineer Peter Vandal leads Taco’s computational fluid dynamics (CFD) design operations. After importing the geometry from SolidWorks software, all of the meshing, simulation and analysis is performed in Simcenter STAR-CCM+, as shown in figure 2. For each pump design the CFD simulation gives a full, three-dimensional representation of the flow and pressures within the pump housing.

“We can take readings at any point in the model, like virtual probes,” explains Vandal. “For example, we can pull out the static pressure or total pressure values at the same points as the probes used in the lab testing, so we can directly compare the Simcenter STAR-CCM+ results with the real-world application.”

This validation of the CFD model gives the team a high level of confidence in the CFD results, along with the predictive insight into performance characteristics such as head, efficiency and best efficiency point (BEP) flow rate. Once Vandal and his team have three or four designs that yield acceptable performance in Simcenter STAR-CCM+, they move on to building and testing their physical prototypes. Even with their ability to rapidly prototype (via 3D printing) the stereolithography (SLA) impellers, each one costs up to $2,500 to build and test. Exploring the performance of numerous digital prototypes in Simcenter STAR-CCM+ provides significant cost and time savings, enabling a high probability of success in a single phase of prototype testing and ensuring a short development time window.

Figure 1: Example of a Taco Comfort Solutions circulator pump.

Simulating the complete pump curve

Vandal and his team run steady-state simulations on each design, testing multiple flow points to establish the BEP flow rate. In an ideal world, pumps would always run near the BEP, but this is not always the case. To prevent field problems and meet customer needs, it is important to look at off-design flow to be sure the pump will be robust over the complete operating curve. Vandal describes three distinct sections: “On the left hand side of the pump curve you can get an excessive droop, which is not acceptable. The BEP lies in the center and on the right hand side you need to examine the operating conditions at high flow rates.”

Taco performs unsteady simulations in Simcenter STAR-CCM+, aiming to examine the entire pump curve.

“We initialize the CFD model with a steady state run at BEP flow rate, then change the boundary conditions so the flow changes towards the extreme flow rate,” says Vandal.

He shared one example of a case that showed an underperforming design on the left hand side of the performance curve (figure 3): “At off-design flow rates the pump flow can become highly unsteady (figure 4). If there is too much drop in pressure on the left hand side of the pump curve, there could be problems with operating a parallel pumping setup. I was able to run an unsteady simulation in Simcenter STAR-CCM+ at 10 percent and 50 percent of the BEP flow rate in gallons per minute to quantify the amount of droop between the maximum head point (50 percent) and near shut-off head (10 percent). I used the same method to simulate alternative designs before we built the SLA impellers for lab testing. The designs that went forward for testing were those which showed good results not only at BEP, but also at low flow rate, with a smaller drop in pressure on the left side of the performance curve.”

Taco has confidence its pump designs can be even more robust, running as efficiently and reliably as possible even when operated off-design.

Figure 3: Example of a performance curve for two test cases. Dotted lines show Simcenter STAR-CCM+ results, solid lines show lab testing results. Case A showed a large drop in pressure (ΔA) between 50 percent BEP (max head) and 10 percent BEP. Redesigning the impeller (case B) decreased this pressure drop (ΔB).

Figure 2: A pump model is designed in CAD software and imported into Simcenter STAR-CCM+ (first), where it is meshed (second) and simulated (third).

Streamlining workflows

Using Simcenter STAR-CCM+ for virtual testing has sped up Taco’s design workflow and reduced the costs associated with physical testing.

“When I think back a few years to the first pumps I worked on, we would order parts for testing, they would be bad and we would have to do the whole design, ordering and testing process again,” says Vandal. “Now that we are using Simcenter STAR-CCM+, we are cutting out this iterative ‘start over’ process and speeding up the complete design cycle.

“When we first started using Simcenter STAR-CCM+, we did not have much lab test data to correlate with the CFD results, so we did not know the best model settings – such as roughness or leakage flows – to use. We now have a library of lab test data that validates the Simcenter STAR-CCM+ results, and know the best model settings to use to get accurate results.”

But Taco is determined to streamline their design process still further. “We are always looking for ways to use the software faster,” comments Vandal. “Any time we spend a couple of hours on something we will say ‘how can we do this in 50 minutes?’ We want to work smarter with the software, not harder.”

Vandal and his team have worked closely with their Siemens dedicated support engineer (DSE) to streamline their simulations.

“It’s great having a dedicated contact at Siemens who knows our processes and works with us to find solutions,” explains Vandal. Taco worked together with their DSE to develop a quick multi-design testing process using the Simcenter STAR-CCM+ part-swapping capability. Once the model has been set up and run in Simcenter STAR-CCM+, part swapping enables Vandal to replace just the impeller or volute with an alternative design, while the CFD model settings and boundary conditions remain unchanged, as in figure 5. Simcenter STAR-CCM+ then rapidly regenerates the mesh, and computes a new solution.

“We use a standardized naming convention in SolidWorks, so when I want to change one part in the Simcenter STAR-CCM+ model, I literally hit the replace part button and run a new simulation,” says Vandal. “We love working this way, as we can test multiple cases one after the other using the same mesh and simulation settings. This not only makes it quick to run multiple simulations, but also gives us confidence that the results will be consistent and repeatable.”

Taco has also created Java macros to automate the mesh-and-run” process, enabling pump curves to be generated automatically. Automated processes like this help Taco work toward their aim of halving their current design process time.

Taco is also looking to the future, aiming to build on the knowledge garnered over the last two years. Greg Case, chief technology officer (CTO), says, “We are relying on our strategic use of CFD simulation to help us beat our competition to market with better performing pumps, and increase market share.”

Vandal explains, “Our major gain from using Simcenter STAR-CCM+ is shortening our iterative design process in a highly competitive industry. We want to know that when we invest in lab testing efforts or part tooling, the results will have a high likelihood of success. Simcenter STAR-CCM+ gives us the confidence that is the case. Essentially, we want to eliminate the feedback loop between lab testing and the design stage so that each pump design has as few lab tests as possible.

“We want to explore digitally and confirm physically rather than the other way around. Given the library of SLA lab test data we now have using both SLA and metal parts, and the confidence we have in the Simcenter STAR-CCM+ data we have generated so far, I want to aim for a future where we no longer use SLA testing but go straight from Simcenter STAR-CCM+ to metal impeller testing. It is a bit risky, but I think it is possible and will save us time and costs, enabling us to bring new, more efficient and reliable pumps to market faster.”

Figure 5: Part swapping allows quick changes to the impeller, keeping the rest of the geometry the same. Results are easily comparable as all mesh and physics settings are identical.

Figure 5: Part swapping allows quick changes to the impeller, keeping the rest of the geometry the same. Results are easily comparable as all mesh and physics settings are identical.

Figure 4: When the pump is operated at flow rates far off-design (first), the flow in the pump clearly becomes highly unsteady with significantly more recirculation visible compared to the flow at the BEP (second).