# 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  
#### 4.1.1 Influences of the Honeycomb Thickness \(l\)  
The large thickness of the honeycomb can obtain a better turbulence reduction performance of the lateral flow; however, the increase of the thickness will lead to the increase of the internal friction loss. In order to obtain the appropriate thickness of the honeycomb, we studied the fluid field characteristics of the test section with the honeycomb when different thicknesses were applied.  
Figure 6 shows the velocity distribution characteristics of the fluid field from the inlet (\(x\) = 0 m) to the outlet (\(x\) = 0.5 m) of the test section, when the honeycomb with different thicknesses is selected. It can be observed that, when the thickness of the honeycomb is 35 mm, the velocity fluctuation of the fluid field in the test section is smaller, and the velocity distribution is more uniform. Figure 7 shows the distribution of the turbulence intensity when the honeycomb with different thicknesses is selected. Figure 7a shows the turbulence intensity along the axial direction from the inlet (\(x\) = 0 m) to the outlet (\(x\) = 0.5 m) of the test section, and Figure 7b shows the turbulence intensity along the lateral direction on the middle area (\(x\) = 0.25 m) of the test section. It can be seen that the turbulence intensity decreases gradually along the axial direction. The turbulence intensity at the center line of the water channel is the largest and decreases symmetrically to both sides. The area with the uniform turbulence intensity is mainly concentrated near the center line (\(-\)0.02 m \(<y\) \(<\) 0.02 m) of the test section. The smallest turbulence intensity can be obtained when the honeycomb with the thickness as 35 mm is selected in this work.  
Figure 6: The velocity distribution characteristics of the fluid field from the inlet to the outlet of the test section when the honeycomb with different thicknesses is selected.  
The velocity inhomogeneity is defined as  
\[\beta=\frac{U_{\max}-U_{\min}}{U} \tag{3}\]  
where \(U_{\max}\) is the maximum velocity, \(U_{\min}\) is the minimum velocity, and \(U\) is the mean velocity.  
Table 3 shows the velocity inhomogeneity and average turbulence intensity of the fluid field in the test section when the honeycomb with different thicknesses is selected. It can be seen that, with the increase of the thickness of the honeycomb, the velocity inhomogeneity and the average turbulence intensity decrease before 35 mm and then increase gradually.  
Figure 8 shows the velocity contour of the fluid field in the middle section (\(z=0.015\) m) of the test section when the honeycomb with different thicknesses is selected. It can be seen that the velocity presents a gradient trend from the two sides to the center. The results show that the velocity distribution of the fluid field in the test section is relatively more uniform when the honeycomb with the thickness as 35 mm is selected. Therefore, in order to obtain the fluid field with a uniform velocity and low turbulence intensity, the intermediate thickness of the honeycomb should be selected. In this work, when the thickness of the honeycomb is 35 mm, the appropriate flow charac  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Thickness** & **25 mm** & **30 mm** & **35 mm** & **40 mm** & **45 mm** & **50 mm** \\ \hline Velocity inhomogeneity \(\beta\) & 1.2198 & 1.2032 & 1.1240 & 1.1514 & 1.1531 & 1.1542 \\ Average turbulence intensity & 0.0564 & 0.0561 & 0.0491 & 0.0544 & 0.0573 & 0.0649 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The velocity inhomogeneity and average turbulence intensity of the fluid field in the test section when the honeycomb with different thicknesses is selected.  
Figure 7: The distribution of the turbulence intensity when the honeycomb with different thicknesses is selected: (**a**) along the axial direction and (**b**) along the lateral direction.