## 3 Methods  
### Model Establishment  
To investigate the stratification effects of porous obstacles, this study designed and comparatively analyzed five storage tanks with different internal structures. As shown in Figure 3, (a) is a traditional storage tank with no internal structures. (b) The storage tank is equipped with an orifice plate obstacle in the middle. Since the orifice plate obstacle performs better when positioned at a certain distance from the bottom of the storage tank, this study places the obstacle at a height of 330 mm from the bottom [6]. Figure 3 (c) shows a storage tank equipped with a porous obstacle. The surface shape of the porous obstacle is shown in (d), and it is filled with small holes as illustrated. The mechanisms of influence for porous obstacles differ from those of orifice plate obstacles. To investigate the impact of different installation methods of porous obstacles on stratification, this study additionally designed storage tanks with three different installation configurations of porous obstacles for energy release simulations. (c) The obstacle is positioned far from the bottom; (e) the porous obstacle is placed near the inlet; and (f) one porous obstacle is installed near both the upper and lower inlets and outlets. In this study, the porous medium model method is used to solve the equations at the locations of the porous obstacles. Therefore, the geometric structure of the porous obstacles is simplified and modeled directly as baffles. Since positioning the outlet near the bottom is more conducive to hydraulic stratification, the hot and cold water inlets and outlets are designed to be located 30 mm from the top and bottom surfaces, respectively [13]. As shown in Table 1, due to the constant variation in the c-h ratio in actual storage tanks, cases E1 to E6 are divided into two categories: the initial c-h ratio for heat release in cases E1, E2, and E3 is 0.38, while for cases E4, E5, and E6, the initial c-h ratio is 0. To obtain more information on the stratification performance of the porous obstacles, this study set three inlet flow velocities: 0.1 m/s, 0.2 m/s, and 0.3 m/s. Figure 2: Research process. Figure 3: (**a**) Type a conventional tanks; (**b**) Type b orifice plate obstacle tanks; (**c**) Type c porous obstacle tanks; (**d**) surface shape of porous obstacles; (**e**) Type e bottom porous obstacle tanks; (**f**) Type f bottom and top porous obstacle tanks. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Case** & **Type** & **c–h Ratio** & **H-T (K)** & **C-T (K)** &
\begin{tabular}{c} **Velocity** \\ **(m/s)** \\ \end{tabular} \\ \hline E1 & a & 0.38 & 360 & 300 & 0.1/0.2/0.3 \\ E2 & b & 0.38 & 360 & 300 & 0.1/0.2/0.3 \\ E3 & c & 0.38 & 360 & 300 & 0.1/0.2/0.3 \\ E4 & c & 0 & 360 & 300 & 0.1/0.2/0.3 \\ E5 & e & 0 & 360 & 300 & 0.1/0.2/0.3 \\ E6 & f & 0 & 360 & 300 & 0.1/0.2/0.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation case classification and parameters. As shown in Figure 3, the storage tank consists of three main components: the tank body, obstacles, and inlets and outlets. The cold water inlet and outlet are located at the bottom, while the hot water inlet and outlet are at the top. The geometric model was established using CREO 9.0, and the simulations were conducted using the commercial software ANSYS FLUENT 2022. In the preprocessing stage, the geometric model was meshed using FLUENT Meshing, primarily employing hexahedral elements to generate a structured grid. Structured grids offer higher solution accuracy and faster convergence rates. The skewness of the mesh quality was controlled to be below 0.5. The mesh configuration is illustrated in Figure 4.  
The number of mesh elements and the time step size can affect the solution accuracy. However, an excessive number of mesh elements and too small a time step can significantly increase the computational burden. Therefore, this study conducted an independence verification by setting up three sets of mesh nodes and three different time step sizes.