## 4 Flow Field Analysis of Corner-Filled Goaf Area Using ANSYS Fluent
### Simulation Analysis of Upper and Lower Corner Fillings in the Working Face  
To evaluate the impact of different corner fillings on goat air leakage and the extent of the oxidation zone, we introduced pre-set filling bodies behind the working face, expanding on the model established in the previous section. We examined three distinct scenarios: C1--filling only the upper corner of the working face, C2--filling only the lower corner of  
Figure 8: Numerical simulation physical model of 22,122 working face in Cuncaota II mine. Figure 9: Schematic comparison between measured and simulated oxidation zones in the goat. the working face, and C3--filling both corners. The pre-set filling bodies were 100 m long, 3 m wide, and 3 m high, with an approximate zero porosity. The ventilation parameters remained consistent with the conditions outlined in the previous study. The specific layout is shown in Figure 10.  
Figure 11 depicts the pressure distribution in the goat at a height of z = 1.5 m, showing continuous changes resulting from various backfilling strategies. The exit pressure on the return air side of the working face corner is set as the reference point at 0 Pa. The highest pressure occurs near the lower corner, driving gas flow within the goat due to pressure differentials. A comparison between the unfilled condition and filling only in the upper corner reveals significant alterations in the pressure distribution within the goat. After filling in the upper corner, the green pressure zone in the deep part of the goat substantially expands, while the light green range of 4-5 Pa experiences a sharp reduction. This indicates a notable increase in pressure in the deep part of the goat and a considerable decrease in the pressure difference between the lower corner and the deep part, ultimately leading to a reduction in overall air leakage from the goat. After comparing the unfilled and only partially filled lower corner areas, it becomes evident that filling the lower corner leads to the dominance of the deep goat by pressure isopleths of 3-4 Pa in the blue area. Furthermore, the high-pressure range significantly decreases, resulting in a decline in pressure within the deep goat. Consequently, an increased pressure difference between the lower corner and the deep goat occurs. Fortunately, the filling material in the lower corner effectively obstructs the majority of airflow from infiltrating the goat. Simultaneously, the reduced pressure difference between the upper corner and the deep goat hampers the backflow of harmful gases into the working face, thereby reducing the accumulation of gas in the upper corner of the goat. Figure 11: Distribution of pressure field in the goat with the different corners of filling bodies. Figure 10: Diagram of the filling body model. Upon comparison of the unfilled area with the region filled with both the upper and lower corners, it is apparent that filling both the upper and lower corners of the working face leads to an increase in pressure within the deep goal. However, the extent of this pressure increase is slightly lower than when only the upper corner is filled. Furthermore, the range of the low-pressure area is slightly larger than when only the upper corner is filled, but it is significantly smaller than when only the lower corner is filled. This indicates that, when both the upper and lower corners of the working face are simultaneously filled, the filling material in the upper corner has a greater impact on the overall pressure changes in the goal. It effectively reduces the pressure difference between the deep goal and the lower corner, thereby minimizing air leakage from its source. Additionally, the majority of airflow within the goal is hindered by the filling material in the upper corner, making it difficult for gases like methane to flow back toward the working face. Figure 12 depicts a contour map showing the distribution of the oxygen concentration in the goat at a height of z = 1.5 m, with both the upper and lower corners filled.