# Impact of Different Nose Lengths on Flow-Field Structure around a High-Speed Train
## 4 Results and Analysis
### Time-Averaged Flow
#### 4.2.2 Time-Averaged Pressure
At \(z\)=1.6 m, the difference of \(|\Delta C_{P\text{ max}}|\) and \(\Delta C_{P}\) values between nose lengths of 4 and 12 m is 0.107 and 0.143, respectively; at \(z\) = 2 m, the difference of \(|\Delta C_{P\text{ max}}|\) and \(\Delta C_{P}\) values between nose lengths of 4 and 12 m is 0.116 and 0.153, respectively; at \(z\)=2.4 m, the difference of \(|\Delta C_{P\text{ max}}|\) and \(\Delta C_{P}\) values between nose lengths of 4 and 12 m is 0.12 and 0.141, respectively; at \(z\) = 2.8 m, the difference of \(|\Delta C_{P\text{ max}}|\) and \(\Delta C_{P}\) values between nose lengths of 4 and 12 m is 0.12 and 0.141, respectively; at \(z\) = 2.8 m, the difference of \(|\Delta C_{P\text{ max}}|\) and \(\Delta C_{P}\) values between nose lengths of 4 and 12 m is 0.115 and 0.15, respectively. The difference of \(|\Delta C_{P\text{ min}}|\) for nose lengths of 4 and 12 m shows a trend of first increasing and then decreasing, while the difference of \(\Delta C_{P}\) has no obvious change trend. When the nose length of the train is 4 m, the height increases from \(z\) = 1.6 m to \(z\) = 2.8 m, and the values of \(\Delta C_{P\text{ max}}\), \(|\Delta C_{P\text{ min}}|\), and \(\Delta C_{P}\) decrease continuously, decreasing by 18.4%, 4.4%, and 10.3%, respectively. \(\Delta C_{P\text{ max}}\), \(|\Delta C_{P\text{ min}}|\), and \(\Delta C_{P}\) at a height of 1.6 m from the TOR decreases with increasing nose length, and the nose length increases from 4 to 12 m, which decreases by 26.5%, 58.5%, and 44.8%, respectively. Properly increasing the length of the nose has an obvious effect on improving the pressure around the train. Figure 13: Pressure coefficient at y = 2.5 m for (**a**) z = 1.6 m, (**b**) z = 2 m, (**c**) z = 2.4 m, and (**d**) z = 2.8 m (black dashed line on left is the nose and that on the right the tail). Figure 14 shows the time-averaged pressure coefficient \(C_{P}\) on the surface at y = 0 m for trains of different nose lengths, with Figure 14a showing \(C_{P}\) on the upper surface and Figure 14b showing \(C_{P}\) on the lower surface. It can be seen from the figure that, with different nose lengths, the \(C_{P}\) on the upper surface near the junction of the streamlined and non-streamlined nose of the head and tail cars is quite different, and the negative pressure amplitude of the head car is larger than that of the tail car. Taking a nose length of 4 m as an example, the negative pressure amplitude of the head car is 28.5% larger than that of the tail car. The pressure amplitude in the boundary-layer region with different nose lengths has little effect. When the nose length increases from 4 to 12 m, the negative pressure amplitude of the head car decreases by 74.1%, and the negative pressure amplitude of the tail car decreases by 71.2%. However, different nose lengths have little effect on the time-averaged pressure distribution on the lower surface, and only the local area exhibits a small difference. In summary, it can be seen that the nose length mainly has a great impact on the pressure distribution near the junction of streamlined and non-streamlined nose, and with increasing nose length the negative pressure amplitude decreases obviously.