# Effect of Topography Truncation on Experimental Simulation of Flow over Complex Terrain
## 6 Conclusions  
A wind tunnel test for simulating flow over complex terrain was conducted in the wind tunnel laboratory of Central South University to investigate the effect of topographic truncation on wind characteristics. The analysis was carried out in two perspectives: mean wind characteristics, including mean velocity and inclination angle, and turbulence characteristics, including turbulence intensity and velocity spectra, which are fundamental parameters for flow characteristic description and are also essential for engineering applications. From the wind tunnel test, conclusions can be summarized as follows:  
1. Experimental results show that the effect of topographic truncation on profiles of mean velocity and turbulence intensity is different for different regions. A greater impact of the truncation was found in windward and leeward regions. The truncation of the terrain leads to a change in topographic features, causing a change in flow behavior upwind, and is the main reason for this difference. Accurate simulation of flow behavior upwind is crucial for repeating mean velocity and turbulence intensity profiles at target locations.
2. By comparing the mean velocity and turbulence intensity, profiles of the inclination angle are more sensitive to topographic changes upstream, or they are more sensitive to changes in upstream flow behavior.  
Figure 10: Metrics on spectra shifts at measurement locations: (**a**) median of the normalized frequency; (**b**) the bandwidth of the normalized frequency.  
3. Overestimation of streamwise velocity spectra was found in cases with the truncated terrain model in the low-frequency range but underestimated in the high-frequency range. Meanwhile, the slope of the spectra is influenced by a less negative value at the inertial subrange. Moreover, the normalized bandwidth representing the 90% energy interval is influenced by the topographic truncation, but the effect relates to the measurement locations. The bandwidth of windward and leeward regions narrows down, while the bandwidth of the valley region broadens.
4. Transition sections used in this study have only limited effectiveness. Transition sections can only curb flow separation at the edge of the terrain model, but the change in flow behavior caused by the absence of topographic features due to topographic truncation cannot be resolved. In addition, the implementation of transition sections at the model edge may introduce additional errors into the experiment.  
Conceptualization, Z.W. and Y.Z.; methodology, X.H. and Y.Z.; software, P.Y.; validation, Z.W., Y.Z and L.L.; formal analysis, Z.W.; investigation, Z.W.; resources, Y.Z.; data curation, P.Y.; writing--original draft preparation, Z.W.; writing--review and editing, Y.Z.; visualization, P.Y. and L.L.; supervision, X.H.; project administration, Y.Z.; funding acquisition, X.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant numbers 52078504, U1934209 and 51925808, and the Science and Technology Innovation Program of Hunan Province, grant number 2021 RC3016.  
Not applicable.  
Data Availability Statement: Data are contained within this article.  
The authors declare