## 4 Conclusions  
Compared with previous studies (as shown in Table 4), this paper adopted more turbulence models to verify the effectiveness of simulating the wind field of a downburst over hills. In addition, vorticity contours were used to examine the transient wind fields obtained from each turbulence model. The separation mechanism of a three-dimensional hill model under a downthrust is further studied by using the POD method. Our analysis leads to several key conclusions. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**References** & **Turbulent Model** & **Research Content** \\ \hline [PERSON] and [PERSON] [21] & RSM & The maximum wind velocity phenomenon. \\ \hline [PERSON] et al. [22] & LES & 2. & Relation between peak wind speed and roughness; Turbulence correlations in the wide frequency range characterized by the turbulent length scales. \\ \hline [PERSON] and [PERSON] [23] & Standard k-\(\varepsilon\), renormalization group \(k\)-\(\varepsilon\) (RNG), realizable \(k\)-\(\varepsilon\), shear stress transport \(k\)-\(\omega\) (SST), RSM, and LES & Comparison of simulation effects of turbulence models. \\ \hline [PERSON] & [PERSON] and [PERSON] [24] & IDDES \(k\)-\(\omega\), SST, Scale Adaptive Simulation (SAS), and LES & Comparison of simulation effects of turbulence models. \\ \hline [PERSON] et al. [25] & Standard \(k\)-\(\varepsilon\), REA, RNG, SST, and RSM & Comparison of simulation effects of turbulence models. \\ \hline  & & 1. & Comparison of simulation effects of turbulence models; The effect of the exact geometry of the bell nozzle and the hexagonal shape of the test chamber on the simulation; The physical characteristics of downburst wind in a WindEEE dome are studied from the perspective of structural wind load. \\ \hline [PERSON] et al. [28] & Differential Reynolds stress model (DSM) and \(k\)-\(\varepsilon\) model & Acceleration phenomenon at the crest of the embankment. \\ \hline [PERSON] et al. [30] & / & The influence that topographic features have on the near-ground wind structure of a downburst. \\ \hline [PERSON] et al. [4] & DES & The profiles of downburst wind speeds as they pass over real topography, and the consequent changes in horizontal and vertical downburst wind speeds. \\ \hline [PERSON] & [PERSON] et al. [31] & REA, RNG, and SST & 2. & Comparison of simulation effects of turbulence models; A semi-empirical model is established for the acceleration effect of the downburst wind field over a hill. \\ \hline  & & 1. & Comparison of simulation effects of turbulence models; The evolution mechanism of the transient wind field structure over the quadratic ideal hill under a downburst is revealed; The flow separation characteristics and the acceleration phenomena of wind fields over hills and flatlands. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: A brief review of related literature that compare turbulence models. For the mean wind field over the 3D hill model, the CFD numerical simulation method can simulate the wind field characteristics of the downburst. The results of the LES model, the DES-RK model, and the REA model are more accurate than other models, and the proportion of errors within 30% is as high as 80%. Furthermore, the simulation effect of each turbulence model is REA \(\approx\) LES > DES. By comparing the fluctuating wind speed, it was found that the simulation performance of each turbulence model in the transient wind field was ranked as follows: LES > DES. When comparing flow separation at the same time, it was found that the flow separation obtained by the DES-SST, DDES-SST, and IDDES-SST models showed little difference. The ring vortex structure simulated by the LES model underwent flow separation earlier than other models, and the vortex structure was more discrete when flowing over the hill model. Additionally, the vortex shedding position from the DES-RK turbulence model was concentrated near the wall, and the interaction between the main vortex and secondary vortex did not develop along the vertical height.