Optimizing the Efficiency and Cavitation of Franklin Electric's High Speed Pumps

Using 3D Inverse Design code TURBOdesign1 for pump blade design and optimization can lead to many advantages even in the manual design process. This is thanks to a more intuitive design process where design input parameters, namely the blade loading, more directly correlate with the pump performance, such as efficiency and cavitation performance.

TURBOdesign1 can be run in script mode and directly linked to external CFD/FEA and optimization tools via TURBOdesign Optima, specifically the TURBOdesign LinkWB module links directly with Ansys Workbench and CFX. “As a Development Engineer I want to make designs, not code integrations between tools”, commented Gabriel. “TURBOdesign LinkWB does exactly that, it requires no scripting at all and works as a plug-and-play solution for optimization with Ansys Workbench”.

The workflow presented above shows how TURBOdesign1 is used as the blade generator within the Workbench environment, allowing a very wide range of design parameters that covered both the meridional shape and blade loading, ultimately influencing the 3D blade shape. The entire workflow takes less than 5 minutes per design on a workstation with 22 Cores, including 3D design, meshing and CFD solution. This is also possible thanks to the post-processing capabilities of TURBOdesign1 that provides both the 3D geometry and also the surface pressure data.

The minimum pressure on the blade surface is automatically calculated by TURBOdesign1 and used as a performance parameter to evaluate inception of cavitation, hence eliminating the need to run more expensive two-phases flow analysis for each design.

TURBOdesign1 being a 3D Inverse Design method, every blade that is generated satisfies the correct Euler Head requirements at the specified volume flow rate and RPM. This ensures the automatic optimization process, even when using large parameters Design of Experiments (DoE) clusters the solution around the specific pump requirements and objective.

The image below plots Head and Minimum Pressure on the blade for a comparative Design of Experiment (DoE) study. The grey dots show the results for an equivalent “conventional” design approach based on varying blade angles, whereas the blue dots show the same process performed with TURBOdesign1.

In the case of optimization based on a “conventional“ approach based on varying blade angle, there is very large variation in pump head and as result it was not possible to create an accurate surrogate mode for optimization so that the tradeoff between efficiency and minimum pressure can be clearly observed. In the case of 3D Inverse Design based optimization, where the blade geometry is modelled by variation in blade loading (blue points), the impeller head is very close to target value. As a result an accurate surrogate model could be established. This surrogate model was then used to select three impeller geometries for further evaluation.

Above illustrates the comparison between the baseline and optimized impeller predictions which confirm that cavitation has been completely eliminated in the optimized impeller. This impeller was then used together with a new volute created by TURBOdesign Volute and the resulting stage was then manufactured and tested. The test showed significant improvement in cavitation margin and 4% increase in stage efficiency.

Conclusion

Using TURBOdesign Suite for a number of years, Franklin Electric has been able to considerably improve their pump performances. Gabriel commented that “By using TURBOdesign within Ansys Workbench, we’ve been able to obtain CFD results on hundreds of impellers literally overnight. This software combination has allowed us to explore hydraulic parameters beyond typical boundaries and ultimately improved pump performance in significantly less time when compared to our traditional design process.” Franklin Electric is now looking at applying similar workflows to the design of multistage pumps.