*Tribology of Machine Elements - Fundamentals and Applications*


**Table 5.**

*Calculation conditions of CFD analysis.*

**Figure 9.**

*CDF analysis results of pressure and velocity distributions on grooved seals.*

the film thicknesses are common. Therefore, the closing forces are different. In addition, the visualization areas are different in the two seals because the calculation area depends on the groove shape intervals.

#### *Groove Shape Optimization on Dry Gas Seals DOI: http://dx.doi.org/10.5772/intechopen.103088*

From the results in **Figure 9**(I), high pressure is generated on the outer region of the seal caused by the hydrostatic effect. However, the high-pressure area in the optimized seal is narrow compared with that of the spiral grooved seal. Moreover, the velocities on the flow in the optimized seal are faster than those in the spiral grooved seal. This is due to groove shape in the outer radius vicinity. The groove shape of the spiral groove is formed along the rotational direction. Consequently, outer air is drawn into the seal and the air velocity is fast. On the other hand, with the optimized seal face, the gas flow velocity in the outer vicinity reduces because the inflow is suppressed by the pump effect of the bending shape groove. As mentioned earlier, reducing the gas inlet flow velocity on the optimized seal face leads to reduce the gas overall leakage.

Moreover, comparing both the Reynolds equation and the CFD results of loadcarrying capacity and amount of leakage, are shown in **Table 6**. As shown in the Table, the load-carrying capacity is in very good agreement with both results. On the other hand, the amount of leakage, there is a little difference in both analytical solutions. This is because the amount of leakage is calculated using pressure difference and it is easy to include the numerical error. Besides, the load-carrying capacity is calculated by the integration of pressure distribution. Therefore, it is considered that the numerical error is very small. However, the difference in the amount of leakages is acceptable.

Finally, the experimental verification of flow visualization is mentioned. The experimental visualization results are picked up from our past research work [21, 22].

The experimental conditions are same as **Tables 4** and **5**, except the groove depth of 70μm and the seal clearance of 50μm. Here, the main purpose of the


#### **Table 6.**

*Comparison of Reynolds equation to CFD.*

**Figure 10.** *Experimental visualization results [21].*

verification is to confirm the qualitative flow difference, therefore we think the comparison is meaningful even if the values between the CFD and experimental visualization are not the same. The specific visualization setup and spec are shown in the previous studies.

**Figure 10** depicts the experimental visualization results of our previous study [21]. The velocity distributions are shown as color arrows. The outer side gas flows strongly into the spiral groove seal face through the boundary as shown in **Figure 10a**. On the other hand, in the case of optimized seal, the flows are very weak compared to that of spiral groove seal. The same tendencies are shown in the CFD analysis results, and the applicability of the optimization was verified experimentally.
