# Effect of Topography Truncation on Experimental Simulation of Flow over Complex Terrain
## 3 Mean wind Characteristics  
### Mean Velocity  
Profiles of streamwise velocity U, which were normalized by the mean velocity at the top height of each location U\({}_{\rm r}\) to reduce the influence of variation in incoming flow velocity, are shown in Figure 4 for four test cases with uniform inflow conditions but different forms of the transition section. For the convenience of analysis and interpretation, Figure 5 provides east-west cutting planes of measurement locations. Figure 3: The test model at wind tunnel: (**a**) OT; (**b**) WTS; (**c**) WTC; (**d**) RTC. Figure 4 shows the normalized velocity profiles of location A1, where obvious differences in the four test cases are found near the ground. The influenced area is approximately 450 m above the ground in true magnitude, in which the profiles of WTC and RTC are higher than the other two. Because A1 sits at the windward of the center mountain near the edge of the terrain model, the speed-up effects generated by transition sections control this area. For OT and WTS, the mean velocity profiles are similar under a height of approximately 400 m. However, it should be noted that the flow behaviors in these two cases are completely different. In case OT, there is a side mountain range running northeast to southwest at the front of location A1. As shown in Figure 5, the mountain peak lies ahead of location A1 with a height of approximately 400 m, leading to a blockage effect and flow separation. Hence, the mean velocity profile in the OT case shows a smaller speed at the part below approximately 400 m. In addition, for the case WTS, the front mountain peak was truncated and created an \"artificial cliff\" with a height of 287 m. Owing to the larger height difference between the terrain model edge and the wind tunnel floor, separation bubbles occurred, and flow separation controlled this region. However, this does not mean that the WTS shows better performance than the WTC and RTC. It is just a special case with a mountain peak at the front of location A1. Moreover, both the WTC and RTC could accelerate the flow near the ground. When the transition section is implemented, the speed-up effect should be considered, which may considerably affect the experimental accuracy, especially for the locations close to the terrain model leading edge. Figure 4: Profiles of mean velocity at measurement locations: (A1) location A1; (A2) location A2; (A3) location A3; (A4) location A4; (A5) location A5. The leeward region, which includes locations A2 and A3, is on the downhill slope to the leeward of the peak. These locations are located north of the island with the location A2 at the slope and location A3 at the foot of the mountain. As shown in Figure 4, the velocity profiles of location A2 in the four cases are similar, but WTS is slightly larger at heights below approximately 600 m. From the cutting plane of location A2 in Figure 5, it shows that the truncated part of topography is the windward slope of the mountain, and the geometry is similar to the transition section of WTC and RTC. However, the case of WTS with a cliff at the edge of the model may result in flow separation. Thus, differences in velocity profiles were observed. For location A3, the results can almost be divided into two parts according to profiles. One is OT and RTC. The other one is WTS and WTC. As shown in Figure 5, there is a mountain peak in the front of location A3. When the terrain model is truncated, the mountain peak has also been cut down, which may lead to disparate flow behavior in the downwind region. Flow separation generated by the mountain peak controls the wind velocity at location A3 to a great extent. However, the ramp transition section can make up this difference instead of the mountain peak to a certain extent by generating flow separation. Coincidentally, [PERSON] [35] studied the wind characteristics in complex terrain and successfully obtained analogous results by replacing the mountain peak with a ramp of a specific slope.