## 6 Comparison of Results Obtained by Two Methods  
The results obtained with GAZBEAR were compared with those from ANSYS CFX. The ANSYS CFX program has been used repeatedly by many engineers and scientists to analyze gas bearings operating under various conditions. It can therefore serve as a benchmark for comparison with other programs. It should also be noted that experimental results for gas bearings lubricated with low-boiling-point fluids are lacking in the available literature. Therefore, an initial verification of the GAZBEAR program was conducted based on calculation results from another program. The GAZBEAR program is part of the MESWIR computational system developed at the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences, which was used in the design of gas bearings for several prototype microturbines [34; 35]. The results of laboratory tests confirmed the correct operation of these bearings across a wide range of rotational speeds. As the microturbine prototypes are not equipped with shaft displacement sensors, the results of these tests cannot be used to directly verify the GAZBEAR program. A comparison of the calculation results obtained for the self-acting bearing using two different programs, GAZBEAR and ANSYS CFX, is shown in Figure 11. The exact values of aerodynamic load capacity obtained by the two methods for selected relative eccentricities are shown in Table 1. A direct comparison of the load capacities on a single diagram clearly shows that, despite the significant differences between the two methods used, there is very good agreement in the results. The curves determining aerodynamic force versus relative eccentricity obtained in GAZBEAR and ANSYS CFX almost overlapped. In the analyzed relative eccentricity range of 0.01-0.6, as the center of the journal moved away from the center of the sleeve (i.e., the journal surface approached the sleeve surface), the load capacity of the bearing increased from approximately 1.1 N to more than 90 N.  
As part of the analysis of the compared results, a root mean square (RMS) coefficient was calculated for the fit of the eccentricity curve from the ANSYS program to the values obtained from the GAZBEAR program, which was approximately 0.0058. This means that the average deviation of the eccentricity values obtained by the two methods was 0.0058. The smaller the RMS value, the better the curve fit, which in this case indicates a very good fit. The error bars are not plotted in Figure 11 because they are so small that they would not be visible on the diagram. The largest absolute error between eccentricity values was 0.0125, and the smallest absolute error was 0.0006. Relative errors were also low, further confirming the high level of agreement between the results obtained from the two programs. Figure 11: Aerodynamic lift of the gas-dynamic bearing vs. relative eccentricity, determined using the GAZBEAR and ANSYS CFX programs. The very good agreement of the methods used is also confirmed by the results regarding pressure distributions on the sleeve surface. The pressure distribution over the developed sleeve surface, obtained using GAZBEAR and ANSYS CFX programs, is shown in Figures 11(a) and 11(b), respectively. The values obtained, despite the different ways of presenting the pressure distributions in the two programs, are almost identical. The static equilibrium semicircles of the gas-dynamic bearing obtained with ANSYS CFX and GAZBEAR programs are also very similar in shape (Figure 13). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Eccentricity [-]** & **Force [N]—GAZBEAR** & **Force [N]—ANSYS CFX** \\ \hline
0.05 & 5.584 & 4.622 \\
0.10 & 11.220 & 9.818 \\
0.15 & 16.967 & 16.096 \\
0.20 & 22.888 & 22.905 \\
0.25 & 29.059 & 29.802 \\
0.30 & 35.580 & 36.390 \\
0.35 & 42.578 & 42.829 \\
0.40 & 50.232 & 49.524 \\
0.45 & 58.780 & 57.739 \\
0.50 & 68.604 & 68.463 \\
0.55 & 80.182 & 81.490 \\
0.60 & 94.268 & 93.584 1  \\ \hline \hline \end{tabular}
\end{table}