## 3 Results and Discussion
### Pints in Inlet Channel
#### 3.3.2 Alternate Arrangement  
The pins are arranged in a staggered pattern above and below the inlet channel, with one to four pairs of pins set at regular intervals, as depicted in Figure 9. Compared to the symmetrical arrangement, the increase in permeation velocity near the inlet is relatively smaller. However, with a deeper airflow within the inlet channel, each pin's corresponding permeation velocity will also experience a sudden drop to some extent, which can be attributed to flow velocity and pressure distribution within the inlet channel, as indicated in Figure 9a-c.  
Figure 9: (**a**) Contour and vector of axial inlet channel velocity, (**b**,**c**) curve of permeation velocity difference and pressure distribution, and (**d**) variance corresponding to different numbers of pins arranged alternately.  
The channel size at the pins of an alternating distribution exceeds that of a symmetrical distribution. Consequently, this leads to smaller changes in front pressure and permeation velocity. Eddy recirculation is also present at the rear of the pins. When combined with the pressure changes depicted in Figure 9c, it is evident that, with the same number of pins, the pressure within the inlet channel will experience a slight increase due to their alternate distribution. This may be attributed to the fact that positioning a pin in a region with higher fluid power allows for stronger disturbance to the fluid and more pronounced recirculation, consequently resulting in greater kinetic energy dissipation.  
Furthermore, a small range of high-permeability areas exist in front of each pin because the flow redirection changes, which is caused by partial blockage. When an alternating arrangement is employed, this high-permeability phenomenon becomes more pronounced within that area. There are two possible reasons:  
The first reason is that under an equal number of pins, the alternating positions are more dispersed, effectively disrupting gas flow at higher speeds compared to symmetrical arrangements, thus influencing airflow direction less significantly than that of alternating distribution [48].  
The second reason concerns the impact of the symmetrical arrangement on airflow direction, which is less significant compared to alternative arrangements. This can be attributed to the substantial variation in size within the symmetrical arrangement area, resulting in higher pressure ahead of the pins. This increase in permeation velocity in front of the pins primarily stems from such pressure differences, while the influence of changes in airflow direction on permeation velocity remains inconspicuous.  
The variance of axial seepage velocity is also compared, as illustrated in Figure 9d. In the model, as the number of pins increases, the variance initially decreases before slightly increasing. When the number of pins is four pairs, there is a slight increase in variance. However, this value remains comparable to that observed with three pairs of pins. In addition, the comparative analysis of the two arrangements reveals that the symmetrical arrangement offers a small advantage in enhancing uniformity with an equivalent number of pins.