*The Influence of Inclined Barriers on Airflow Over a High Speed Train under Crosswind… DOI: http://dx.doi.org/10.5772/intechopen.112751*

from the top side of the barrier. And the train is surrounded by the low-velocity air caused by the right barrier and the flow velocity around the train is almost even. However, when the angle changes to *θ* = +2.5°, +5.0°, +7.5°, and +10.0°, the function of the right barrier mentioned above weakens. The area of the low-velocity region caused by the right barrier is reduced and the distribution of flow velocity on the left of the train becomes unequal correspondingly. As shown in **Figure 3g–j**, when the angle becomes a negative value, the flow velocity on the left side of the train increases and becomes larger than that without a barrier. As a result, the velocity unevenness of the flow field around the train is significantly increasing.

**Figure 4** shows the velocity vectors around the train and barriers. Without the barriers, the flow separations happen from the train's leeward side and then leave the surface and are involved in the leeward vortex. When the barriers are induced, the flow separations begin from the barrier, and the train is surrounded by vortices. As a result, the difference in velocity between the left and right sides of the train decreases, and the velocity on the windward of the train is lower than that on the leeward. However, when the inclined angle changes from positive to negative, the velocity on the leeward of the train increases significantly.

To investigate the effect of barriers and inclined angles on the pressure of the train, **Figure 5** depicts the total pressure contours. Without the barrier, the pressure on the right side of the train is apparently higher than on the left side because of the

#### **Figure 4.**

*The velocity vectors (a) without barriers, (b)* θ *= 0°, (c)* θ *= +2.5°, (d)* θ *= +5.0°, (e)* θ *= +7.5°, (f)* θ *= +10.0°, (g)* θ *= 2.5°, (h)* θ *= 5.0°, (i)* θ *= 7.5°, and (j)* θ *= 10.0°.*

**Figure 5.**

*The total pressure contours (a) without barriers, (b) θ = 0°, (c) θ = +2.5°, (d) θ = +5.0°, (e) θ = +7.5°, (f) θ = +10.0°, (g) θ = 2.5°, (h) θ = 5.0°, (i) θ = 7.5°, and (j) θ = 10.0°.*

crosswind. It should be stated that the pressure on the left side of the train is approximately identical. When two barriers with *θ* = 0° are placed, a low-pressure zone is formed between two barriers. The pressure gradient in this low-pressure zone is small and the relatively low pressure occurs around the top of the left barrier. When the angle increases to +2.5°, the pressure on the right side of the train increases slightly. However, there is one noticeable lower pressure region between the left barrier and the train, which also leads to the pressure gradient. When the inclined angles are negative value, as seen in **Figure 5g–f**, the area of the lower pressure region increase and occupies almost the whole zone between the left barrier and the train. Moreover, when the inclined angle of barriers varies, the pressure gradient between the train and the right barrier is always small.

To analyse the flow pattern characteristics, the turbulence intensity is calculated to show the turbulence level, which is presented in **Figure 6**. Firstly, the existence of the barriers and the inclined angle affect the flow pattern characteristics. Without the barriers, the high turbulence intensity occurs on the train's leeward side, and the turbulence intensity on the windward side is almost equal to 0. However, when two barriers with *θ* = 0° are placed on both sides of the train, the turbulence intensity around the train is affected significantly. Both the windward and leeward sides experience a rise in turbulence intensity. The windward side, which is between the train and the right barrier, has larger turbulence intensity than the leeward side. Besides,

*The Influence of Inclined Barriers on Airflow Over a High Speed Train under Crosswind… DOI: http://dx.doi.org/10.5772/intechopen.112751*

#### **Figure 6.**

*The turbulence intensity contours (a) without barriers, (b) θ = 0°, (c) θ = +2.5°, (d) θ = +5.0°, (e) θ = +7.5°, (f) θ = +10.0°, (g) θ = 2.5°, (h) θ = 5.0°, (i) θ = 7.5°, and (j) θ = 10.0°.*

the turbulence intensity on the right side of the right barrier is adjacent to 0. As the barrier inclined angle increases to +2.5°, the turbulence intensity decreases and the diminishment is more significant between the left barrier and the train, which shows the effect of barriers on the turbulence intensity difference on both sides. However, when the inclined angle increases to +5.0° and +7.5°, the turbulence intensity difference between both sides decreases. That's to say, the difference between the leeward and windward sides of the train becomes small. When the inclined angle increases from +7.5° to +10.0°, the difference increases and the turbulence intensity on the leeward of the train is slightly larger than on the windward. When the inclined angle becomes minus, the turbulence intensity changes slightly.

**Figure 7** shows the effect of barrier inclined angle on the drag force coefficient, lift force coefficient, rolling moment coefficient, and lee-rail rolling moment coefficient. Firstly, it can be found that using the barriers with a positive inclined angle cannot decrease the drag coefficient. The barriers with zero or negative angles can decrease the drag coefficient. The barriers with a positive inclined angle cause a positive drag coefficient of the train, and the barriers with a negative angle lead to a negative value. Besides, the absolute value of the drag coefficient of positive angles is larger than those of negative ones. This can be analysed by comparing two types of barriers. The positive angles of barriers lead to the narrower space around the train. It should be

**Figure 7.**

*The aerodynamic coefficients: (a) drag force coefficient, (b) lift force coefficient, (c) rolling moment coefficient, and (d) lee-rail rolling moment coefficient.*

stated that the barriers with zero inclined angle have the smallest value of drag coefficient. As for the lift coefficient, the existence of barriers is beneficial to the diminution of the lift coefficient regardless of the inclined angle. The zero inclined angles can cause the smallest lift coefficient. The barriers with positive angles lead to the positive value of the lift coefficient and the negative angles cause the negative value, which is similar to the effect on the drag coefficient. Concerning the rolling moment and the lee-rail rolling moment coefficients, the presence of barriers can decrease them. These parameters are important for the train, which is because they are answerable for the loading and unloading of wheelsets. It is obvious that the existence of barriers with any inclined angles, including zero, can decrease the rolling and lee-rail rolling moment coefficients. As the inclined angle of the barrier become θ = +5.0°, the value of the rolling moment coefficient become the minimum. And then when the angle increases, the value also increases. The effect of inclined angle on the lee-rail rolling moment coefficient is more distinct. The positive inclined angle leads to the negative lee-rail rolling moment coefficient and the negative angle cause the positive coefficient.

To demonstrate the impact of various types of barriers (with barriers or not, barriers inclined angle), the effects of barrier type on aerodynamic coefficients are

*The Influence of Inclined Barriers on Airflow Over a High Speed Train under Crosswind… DOI: http://dx.doi.org/10.5772/intechopen.112751*

**Figure 8.**

*The effects of barrier type on aerodynamic coefficients, (a) drag force coefficient, (b) lift force coefficient, (c) rolling moment coefficient, and (d) lee-rail rolling moment coefficient.*

shown in **Figure 8**. In summary, to reduce the aerodynamic coefficients of the train, the barriers with zero inclined angle are the most optimal choice. It appears that the barriers with a positive inclined angle have an inverse effect on the drag coefficient. But the vertical barrier with zero inclined angles has the same effect as the negative ones. As for the lift coefficient, one can find that the existence of any barriers, including the zero inclined angle barriers, leads to a similar influence on the lift coefficient of the train. The same trend also happens for the lee-rail rolling moment coefficient and rolling moment coefficient.
