## 5 Conclusions and Future Work  
Firstly, the numerical model of landing gear was established, and the feasibility of the simulation model was verified by experiments. Then according to the simulation results, the wind speed effect on the flow and acoustic characteristics of the minor cavity structures in a two-wheel landing gears were analyzed, and the following conclusions were drawn:  
For the flow characteristics of the brake disc, at the wind speed of 55 m\(\cdot\)s\({}^{-1}\)-75 m\(\cdot\)s\({}^{-1}\), the vortexes interaction is enhanced, resulting in vortex energy dissipation, so that the increment of pressure fluctuation amplitude is less than 34 m\(\cdot\)s\({}^{-1}\)-55 m\(\cdot\)s\({}^{-1}\). For the flow characteristics of the torque link, with the increase of speed, the obstruction at the lower hole of the torque link decreases, and many vortices flow out of the lower hole and are dissipated, so that the pressure fluctuation amplitude of 75 m\(\cdot\)s\({}^{-1}\) almost does not increase compared with 55 m\(\cdot\)s\({}^{-1}\).  
Furthermore, the sound pressure of each component was extracted, and their noise characteristics were analyzed under different wind speeds. It was found that: (I) The contribution of each component's sound pressure level under different wind speeds was as follows: shock strut > tire > torque link > brake disc. (II) At the speed of 34 m\(\cdot\)s\({}^{-1}\) to  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Velocity** & **Tire** & **Shock Strut** & **Torque Link** & **Brake** \\ \hline \multirow{3}{*}{OASPL/dB} & 34 m\(\cdot\)s\({}^{-1}\) & 92.7 & 98.8 & 85.8 & 74.5/73.9 \\ \cline{2-6}  & 55 m\(\cdot\)s\({}^{-1}\) & 104.6 & 110.9 & 98.6 & 90/91.1 \\ \cline{2-6}  & 75 m\(\cdot\)s\({}^{-1}\) & 111.6 & 119.3 & 102.9 & 98.7/96.6 \\ \hline \hline \end{tabular}
\end{table}
Table 4: OASPL of each component at different wind speeds.  
Figure 24: SPL evolution with frequency of the same part under different wind speeds. (**a**) Shock strut (**b**) Tire (**c**) torque link (**d**) brake (left) (**e**) brake (right).  
55 m\(\cdot\)s\({}^{-1}\), the contribution of each component to the total noise increases with the increase of the speed. Moreover, the amplitude of the sound pressure level of the torque link and brake disc also increases significantly, which has a great impact on the total noise. (III) At the speed of 55 m\(\cdot\)s\({}^{-1}\) to 75 m\(\cdot\)s\({}^{-1}\), the increase of total sound pressure level mainly comes from the main components such as shock strut and tire, and the small components such as brake disc and torque link make very little contribution to the total noise.  
In conclusion, this study investigated the effects of wind speed on the flow and acoustic characteristics in a two-wheel landing gear. In the next step, according to this research result, an optimal design scheme of landing gear noise reduction is expected to be proposed, with experiment to be conducted to do the validation. In addition, it is necessary to study other configurations, such as the four-wheel and the six-wheel, so as to achieve more understanding of the landing gear.  
L.H.; original paper writing and editing, numerical simulation and analysis. K.Z.; experimental testing, data analysis, project administration and financial support. J.L.; experimental test. V.K.; Experimental testing and writing instruction, I.B.; English writing instruction, T.Z.; Guidance on software use and parallel computing. All authors have read and agreed to the published version of the manuscript.  
This work was sponsored by the National Natural Science Foundation of China, under the grant number 11902340.  
Not applicable.  
The authors want to thank the [PERSON] and [PERSON] in CARDC for their help in numerical simulation.  
The authors declare no conflict of interest.