# CFD and Experimental Comparison for Micro-Pump Performance in Space Applications: A Case Study
## 4 Conclusions  
This study presents a case study comparing the CFD results with experimental data for small-scale centrifugal pumps. A fast and efficient method was used for design and testing, combining early stage design tools, 3D CFD optimization, and rapid prototyping with high-precision 3D printing. The approach helped address common challenges in small-scale pumps, especially the combined influence of Reynolds and Taylor numbers on labyrinth performance, which strongly affect efficiency and losses. Important factors such as labyrinth  
Figure 26: Comparison between experimental and empirical adjustments of CFD analysis. Figure 25: Comparison between experimental and native CFD analysis. shape, surface roughness, turbulence models, and inlet flow conditions were carefully studied to understand their impact on both simulations and experimental outcomes. While mesh sensitivity was analyzed in critical subcomponents (the impeller and labyrinth), a full grid convergence study of the entire pump assembly was not conducted. This limitation will be addressed in future work through a more comprehensive mesh refinement analysis to enhance the reliability of global performance predictions. Results showed that LES provides more accurate predictions of wall shear stress within the labyrinth, while most RANS models, particularly the k-epsilon model, tend to over-predict frictional effects. Among the RANS models, the standard k-epsilon formulation proved to be the most credible due to its conservative and consistent performance. Surface roughness significantly affected seal flow and outlet pressure, while inlet turbulence intensity had a negligible impact, likely due to dominant geometry-induced turbulence. The SST model, though more dissipative, highlighted the sensitivity of pressure predictions to turbulence modeling choices. Through comparative analysis of CFD simulations and experimental data, significant discrepancies were identified, particularly in the labyrinth region. Using both RANS and LES for labyrinth flow and RANS for the entire pump assembly, the simulations successfully captured key performance metrics. The results emphasized the critical roles of surface roughness and turbulence modeling in performance predictions. Notably, the application of simple scaling coefficients for mass flow and pressure successfully aligned the CFD results with experimental measurements across all speedlines. Although the transferability of the scaling coefficients to other pump configurations remains uncertain, the concept of correcting the CFD results through scaling factors--rather than more complex methods--offers a practical solution to mitigate macroscopic discrepancies between numerical predictions and experimental data. This insight provides a valuable framework for the future design, prototyping, and optimization of small-scale pumps. Conceptualization, V.D., C.D., I.S.V. and R.M. ; methodology, O.D., V.D., C.D., I.S.V. and R.M. ; software, O.D., V.D. and I.S.V. ; validation, O.D., V.D. and C.D. ; formal analysis, O.D., V.D. and I.S.V. ; investigation, O.D., V.D. and C.D. ; resources, O.D., V.D. and R.M. ; data curation, O.D., V.D., C.D. and I.S.V. ; writing--original draft preparation, O.D., C.D. and I.S.V. ; writing--review and editing, V.D. and R.M. ; visualization, O.D. and V.D. ; supervision, R.M., project administration, R.M., funding acquisition, R.M. All authors have read and agreed to the published version of the manuscript. The presented work was performed under \"NUCLEU\" programme, in the frame of the National Research, Development, and Innovation Plan 2022-2027, carried out with the support of the Romanian Ministry of Research Innovation and Digitalization, project no. PN23.12.06.01 and \"Development of a Closed Impeller Using Advanced Manufacturing\", contract no 4000137441/22/NL/MG/ces, funded by the European Space Agency (ESA). Not applicable. The data presented in this study are available on request from the corresponding author.