# CFD and Experimental Comparison for Micro-Pump Performance in Space Applications: A Case Study
## 3 Results
### CFD and Experimental Data Comparison  
To ensure a comprehensive evaluation of centrifugal pump performance, the manufactured pump components were 3D scanned to identify deviations introduced during the manufacturing process. These deviations were incorporated into the numerical simulations, and a comparative study was conducted at the duty point to assess the impact of surface roughness. Three surface conditions were considered: an ideal case (0 \(\upmu\)m), the measured average for In625 (16 \(\upmu\)m), and a worst-case scenario (40 \(\upmu\)m). Additional parameters varied in the simulations included inlet turbulence intensity levels (1%, 5%, and 10%) and the choice of turbulence model. Figure 18 presents the pump performance in terms of static pressure distribution and total pressure at the outlet. To further evaluate the influence of the turbulence model in the labyrinth area, the ratio of seal leakage flow to useful flow is also compared (Figure 18c). Figure 17: Wall shear stress area integrated: (**a**) over the rotating labyrinth and (**b**) over the stationary casing. Surface roughness plays an important role in estimating both seal leakage flow and total/static pressure at the outlet. For the k-epsilon model, three surface roughness values were applied (0 \(\upmu\)m, 16 \(\upmu\)m, and 40 \(\upmu\)m), resulting in performance differences of up to 7%. Additionally, the influence of inlet turbulence intensity (TI) was evaluated through sensitivity tests using values typically encountered in turbomachinery applications (e.g., 1%, 5%, and 10%). The results, obtained using the RNG (Renormalization Group) k-epsilon model, showed negligible differences in key flow parameters. This insensitivity is attributed to the dominance of geometry-induced turbulence generation--particularly in the blade passages and labyrinth seals--where local shear layers and strong flow acceleration rapidly overwhelm any differences in upstream TI. This indicates that inlet turbulence intensity is not a critical parameter for this particular case. Similar conclusions have been reported in the literature. For instance, [PERSON] and [PERSON] [44] noted that, in internal turbomachinery applications, the inlet TI has minimal impact due to rapid turbulence development within the domain. [PERSON] [45] similarly emphasized that in high-shear flows, the influence of boundary conditions on turbulence diminishes quickly as the flow becomes fully turbulent. In terms of turbulence model influence, the SST model predicted higher pressure losses and lower head values compared to all other models. To better approximate the physical  
Figure 18: Comparison of pump performances obtained using different turbulence models, surface roughness and inlet turbulent intensity: (**a**) Static pressure outlet; (**b**) Total pressure outlet and (**c**) Seal mass flow/useful flow. behavior, \(k\)-epsilon model variants incorporating rotation and curvature compensation terms were also investigated. For the RNG model, similar values were obtained for the static and total pressure distribution at the outlet, and in this case, wall roughness had minimal influence on pump performances. The standard \(k\)-epsilon formulation appeared to be the most conservative in predicting secondary flows and total pressure, making it the most credible model for this study. The EARSM (Explicit Algebraic Reynolds Stress Model) produced results closely aligned with the k-epsilon model across all key parameters. Based on this findings, subsequent numerical simulations were conducted using a wall roughness of 16 \(\upmu\)m, a turbulence intensity of 5%, and the k-epsilon turbulence model. Figure 19 illustrates the \(y+\) distribution along the impeller blades, indicating a maximum value of approximately 30 near the trailing edge. Near the leading edge, the \(y+\) value also approaches 30, although this value is not uniform along the blade height.