# CFD and Experimental Comparison for Micro-Pump Performance in Space Applications: A Case Study
## 3 Results
### CFD and Experimental Data Comparison
Despite these variations, the \(y+\) values remain within the acceptable range recommended for the k-epsilon model, ensuring the validity of the simulation results. Figures 20 and 21 present results for the nominal point at maximum rotational speed. Figure 20a shows the pressure distribution, revealing a uniform pattern at the impeller exit with no signs of flow detachment on the impeller blades. Figure 20b provides further detail, confirming these observations and highlighting the stability of the flow characteristics at maximum rotational speed. Figure 21a shows that the velocity in the front labyrinth is lower compared to other regions of the impeller. The velocity profile gradually increases as the fluid approaches the impeller blades, indicating acceleration of the flow. In contrast, Figure 21b reveals a higher velocity distribution in the back labyrinth. This increased velocity is driven by higher pressure and the kinetic energy transferred to the fluid by the impeller blades, resulting in a more dynamic flow profile in that region. Backflow in both labyrinths is minimal, indicating effective flow management within the impeller system. The minimal backflow results in a small recirculation zone in the front labyrinth region, ensuring stable and predictable flow patterns. The limited extent of this recirculation does not significantly affect the overall performance of the impeller, thereby contributing to the efficient operation of the centrifugal system. The following results present the total pressure variation and torque for three operating speeds corresponding to the studied centrifugal pump. Figures 22a, 23a and 24a illustrate the total pressure distribution across the pump at different rotational speeds, highlighting the influence of the volume on the pump's performance. A significant pressure drop is observed in the solute and outlet duct as the mass flow rate increases. This behavior is consistent across all rotational speeds, indicating that higher flow rates lead to greater  
Figure 19: The \(y+\) distribution on the impeller blades. pressure losses due to increased friction and flow separation within the solute and outlet duct. The torque results (Figures 22b, 23b and 24b) exhibit a typical trend, with torque increasing alongside mass flow rate. This outcome is expected, as higher flow rates require more energy input from the impeller to sustain the flow, thereby increasing torque demand. This trend remains consistent across the different rotational speeds, confirming the direct relationship between mass flow rate and torque in centrifugal pumps operation. Figure 21: Velocity in stationary frame back flow region in (**a**) top labyrinth and (**b**) bottom labyrinth (very low, because of seal). Figure 22: Speedline map 80% from the nominal speed for (**a**) total pressure; (**b**) torque. Figure 25 shows a comparison between the CFD results and experimental data at three rotational speeds, highlighting notable discrepancies, especially at the nominal speed and higher mass flow rates. To explore the consistency of these deviations, simple empirical scaling factors were applied uniformly across the performance map: mass flow was multiplied by 0.85 and static pressure by 0.96 (Figure 26). This empirical adjustment reduced the global offset between CFD and experimental results, allowing a better visual alignment of trends across the speedlines. It is important to note that these scaling factors are not derived from a physical model and should not be interpreted as validated corrections. These adjustments are used solely to illustrate the consistent offset observed between simulation and experiment and do not represent a validated correction. The intent is to explore the nature of the mismatch, not to imply physical accuracy or general applicability of the scaling factors. The majority of pressure losses occur within the solute and outlet pipe, where surface roughness has a substantial impact on the accuracy of pressure loss estimations.