## 5 Verification Test of Micro Texture Drag Reduction Characteristics  
To verify the drag reduction effect of the streamwise micro-texture, half of the bearing bush is made of brass material, and the other half of the smooth bearing bush is used as the test reference, as shown in Figure 19, and the bearing test bench is on the right.  
The inner radius of the bearing bush is 30 mm, the total axial length is 72 mm, the axial length of the micro texture is 52 mm, the width of the micro texture is 200 \(\upmu\)m, the depth is 100 \(\upmu\)m, and the micro texture envelope angle is 22.5\({}^{\circ}\) and is set at the outlet of the divergent wedge according to the loading conditions.  
The experimental loads are 650 N, 750 N and 1150 N, respectively, and the average speed of the bearing speed is 50 r/min, 75 r/min, 100 r/min, 125 r/min, 150 r/min, 175 r/min and 200 r/min, respectively. The lubricating oil used in the experiment is 45 # lubricating oil.  
Theoretically, the viscosity changes with the change of pressure and temperature. However, because half of the bearing bush is used in the experiment, and the other half of the journal is immersed in an open oil groove, the temperature change is small, and the dynamic viscosity is approximately a constant, which is taken as \(\eta=0.34\) Pa \(\cdot\) s. Figure 20 shows the measured friction coefficient of smooth bearing shells under different loads and different rotating speeds.  
Figure 19: Bearing bush and test bench with streamwise texture.  
Figure 18: Influence of transverse texture position on dimensionless shear force on moving wall.  
Since the friction coefficient is the ratio of shear force to a corresponding load, the variation law of the shear force and friction coefficient is basically the same. With the increase of rotating speed, the wall friction coefficient tend to increase; in addition, increasing the load will increase the wall shear force and friction coefficient. Figure 21 shows the friction coefficient measured by the streamwise textured bearing bush under different loads and different rotating speeds.  
It can be seen from the test data that the shear force and friction coefficient of the bearing bush with local streamwise micro-texture are smaller than those of the smooth bearing. Taking the smooth bearing test data as a reference, the dimensionless shear force is calculated as shown in Figure 22.  
From Figure 22, the dimensionless shear force in the whole region is less than 1, that is, the textured bearing bush can obtain a wall shear force lower than that of the smooth bearing bush, and the drag reduction rate is better than that of the high-speed state at low speed. However, the relationship with the load did not show up.  
Figure 21: Comparison between friction coefficient and simulation results under test conditions of axial bearing with flow direction texture.  
Figure 20: Comparison between friction coefficient and simulation results under smooth bearing test conditions.  
Compared with the simulation results, the friction force and friction coefficient of the surface texture are slightly lower in the experimental results, because the ideal airtight state cannot be achieved due to the limitation of experimental conditions, and part of the friction loss is carried away by the oil. Additionally, shear force is higher than the experimental measurement results, this is because the calculation of the shear stress is associated with speed, without considering energy loss and under the influence of external factors, with the increase of rotational speed, the simulation for the shear stress calculation results is slightly higher than that of the experimental results, but the overall trend, which verifies the correctness and effectiveness of the simulation method.