# Enhancing Flow Field Performance of a Small Circulating Water Channel Based on Porous Grid Plate
## 4 Discussions of the Fluid Field Characteristics
### Influences of the Honeycomb
#### 4.1.2 Influences of the Honeycomb Porosity \(q_{1}\)  
The rectifying characteristics of the honeycomb are mainly related to the porosity but not to the shape of the honeycomb (circle, hexagon, and square) [19]. When the honeycomb with the thickness as 35 mm is selected, the influences of porosity on the flow characteristics are studied. Figure 9 shows the velocity distribution statuses of the fluid field from the inlet (\(x\) = 0 m) to the outlet (\(x\) = 0.5 m) of the test section, when the honeycomb has different porosities. As can be seen from Figure 9, the uniform velocity distribution can be obtained in the region from \(x\) = 0.05 m to 0.35 m. Figure 10 displays the distribution characteristics of the turbulence intensity on the middle area (\(x\) = 0.25 m) of the test section when the honeycomb with different porosities are used. The turbulence intensity results along the axial direction and lateral direction of the test section are shown in Figure 10a,b respectively. Table 4 shows the velocity inhomogeneity and average turbulence intensity of the fluid field in the test section when the honeycomb with different porosities is applied. The results show that, with the increase of the porosity, the velocity inhomogeneity and the average turbulence intensity of the test section decrease to a certain value and then increase gradually.  
Figure 8: The velocity contour of the fluid field in the middle section (\(z\) = 0.015 m) when the honeycomb with different thicknesses is selected.  
Figure 11 shows the turbulence intensity contours of the entrance cross-section, middle cross-section and exit cross-section of the test section when the honeycomb with different porosities is selected. As can be observed, the turbulence intensity gradually decreases from the entrance cross-section to the exit, and the turbulence intensity gradually increases from both sides to the middle and from the bottom to the free surface. Besides, by comparing the results under different conditions, it can be concluded that, when the porosity of the honeycomb is 0.6361, a better fluid field quality of the test section can be obtained. As a large porosity can reduce the damping performance of the honeycomb, and a small porosity can weaken the rectification effect. In order to achieve the required fluid field characteristics in the test section, the honeycomb with a moderate porosity should be selected. In this work, the honeycomb with a porosity of 0.6361 was selected for the designed circulating water channel.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Porosity** & **0.5026** & **0.6013** & **0.6361** & **0.6599** & **0.7088** \\ \hline Velocity inhomogeneity \(\beta\) & 1.1260 & 1.1251 & 1.1240 & 1.1247 & 1.1256 \\ Average turbulence intensity & 0.0527 & 0.0500 & 0.0491 & 0.0494 & 0.0511 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The velocity inhomogeneity and average turbulence intensity of the fluid field in the test section when the honeycomb with different porosities is applied.  
Figure 10: The distribution characteristics of the turbulence intensity when the honeycomb with different porosities is used: (**a**) along the axial direction and (**b**) along the lateral direction.  
Figure 9: The velocity distribution of the fluid field from the inlet to the outlet of the test section when the honeycomb has different porosities (\(q_{1}\)).