## 6 Conclusions  
In this study, a comparison verification test of the bearing dry running performance was conducted. CFD numerical simulation models were established for two types of double-row TBRs with different rib structures, and the lubricating oil flow characteristics in the bearing cavity in both fully lubricated and oil loss states were studied. The distribution law of the bearing lubricating oil was explored under different lubricating oil flow rates and rotational speeds. The research results show that:  
1. Through a comparative test of the two types of double-row TBRs with different rib structures, it shows that the internal lubrication condition of the double-row TBR with the outer ring rib structure is better than that with the inner ring rib structure.
2. In the fully lubricated state, the double-row TBR with the outer ring rib structure has a better lubrication condition than that with the inner ring rib structure, the oil volume fraction of the double-row TBR outer ring wall of the outer ring rib structure is 11.296 times higher than that of the inner ring rib structure. The rib can effectively prevent the lubricating oil attached to the inner/outer ring wall from being thrown out of the bearing cavity.
3. In the loss of lubrication state, the lubrication effect of the bearing with the outer ring rib structure is still better than that with the inner ring rib structure. In the final stage of the loss of lubrication, the volume fraction of the bearing flow field of the outer ring rib structure is twice that of the inner ring rib structure  
This article uses a discrete method to study the changes in the distribution of oil and gas in the bearing under the condition of loss of lubrication. In the future, it is expected that the dynamic grid or the slip grid can be used to analyze this process of the bearing. The bearing structure optimization can be guided by studying the influence of changes in bearing structure parameters on the distribution of oil and gas in the bearing.  
Figure 20: Changes in the volume fraction of lubricating oil in the bearing cavity during oil loss.  
**Author Contributions:** Conceptualization, W.Z.; methodology, R.Z. and F.L. ([PERSON]); simulation, X.T.; experiment, W.Z. and. X.T.; validation, X.B., R.Z. and W.Z.; data curation, X.B.; writing--original draft preparation, W.Z.; writing--review and editing, R.Z. and X.B.; supervision, W.Z. and X.T.; project administration, F.L. ([PERSON]); funding acquisition, W.Z., X.W. and F.L. ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural ScienceFoundation of China (52075241) and the National Key Laboratory of Science and Technology on Helicopter Transmission, Nanjing University of Aeronautics and Astronautics (Grant No. HTL-O-20 KO2).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
**Nomenclature**  
\begin{tabular}{l l} TBR & Tapered roller bearings \\ CFD & Computational fluid dynamics \\ MRF & Markov Random Field \\ VOF & Volume of Fluid \\ \end{tabular}