# Effect of Topography Truncation on Experimental Simulation of Flow over Complex Terrain
## 3 Mean wind Characteristics
### Inclination Angle  
The inclination angle means the vertical flow velocity is normalized by the horizontal velocity, which is the most intractable issue in the application of the transition section. Because of transition sections with nearly slope geometry, flow is accelerated through the transition section. This could not be avoided due to the altitude difference between the model edge and the wind tunnel floor, whichever type of transition curve was used. Additionally, this issue can only be minimized by keeping the distance between measurement locations and the model edge long enough to reduce the adverse impact of the transition section.  
Figure 6 shows profiles of the inclination angle at the measurement locations. The profiles are distinctly different from OT at almost every location, particularly in the region near the ground. For location A1 in the windward region, the inclination angle profiles corresponding to the terrain model with a transition section show analogous shapes to OT compared to the completely different profile in the terrain model without a transition section. The flow separation that occurred at the leading edge of the terrain model in the case of WTS greatly changed the profile and resulted in a negative value of inclination angle at the lower part.  
At A2 and A3 in the leeward region, the profiles of the inclination angle in cases with transition sections are quite different from OT with a negative value. Although the profiles of WTS are not the same as those of OT, they are numerically closer, which indicates that when better velocity profile results are obtained, the additional inclination angle induced by the transition section cannot be ignored.  
In the valley region, there are two measurement locations: A4 and A5. Due to the influence of flow separation in the previous analysis of mean velocity, the profiles are almost unchanged in different cases. However, it is entirely diverse in profiles of inclination angle. The inclination angle profiles in the cases of WTS, WTC, and RTC are almost opposite that of OT at heights below approximately 450 m for locations A4 and A5. Positive values have been observed in the region near the ground in the case of OT, while negative values have been found in the other cases. As shown in Figure 6, there is only a single peak ahead of locations A4 and A5. According to previous studies, flow separation off a peak or the edge of a bluff body creates a detached shear layer whose character depends strongly on the separation location [36]. For the single peak topography, separation occurs over crests and on the windward face, while the upwind topography of multiple peaks may advance the separation location. Thus, when the terrain model has been truncated, the single peak topography may be changed to multiple peaks by \"artificial cliff\", and locations of the valley region show opposite inclination angles with OT. For this reason, the values of the inclination angle at locations A4 and A5 become negative in the cases with the truncated terrain model. Additionally, the differences in the cases of WTS, WTC, and RTC indicate that the separation location is determined not only by the slope of the peak but also by its geometry.  
Profiles of inclination angle show more sensitivity to upwind topography than mean velocity. Although the same results of mean velocity were obtained, the opposing results were observed in inclination angle such as at locations A4 and A5. Implementing transition sections in the simulation reduces the adverse effect of flow separation at the leading edge of the terrain model to a certain extent, but there is still a discrepancy compared with the original terrain.  
Figure 6: Profiles of inclination angle at measurement locations: (A1) location A1; (A2) location A2; (A3) location A3; (A4) location A4; (A5) location A5.