# Structural Design and Optimization of Herringbone Grooved Journal Bearings Considering Turbulent
## 3 Results
### The Influence of Helix Angle on the Performance of HGJBs  
The helix angle has a direct effect on the direction of the lubricating oil flow in the HGJBs. We kept other parameters unchanged, took the helix angle as 15\({}^{\circ}\), 30\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), and 75\({}^{\circ}\); and analyzed the influence of the helix angle on the performance of bearings with different structures as shown in Figure 16.  
Figure 16 shows that as the helix angle increases, the bearing load capacity of the bearing gradually increases to the maximum value and then decreases rapidly at a faster rate. It shows that as the helix angle gradually increases, the pumping effect of the bearing  
Figure 16: The influence of helix angle on the performance of HGJBs: (**a**) Dimensionless load capacity (**b**) Side leakage (**c**) Dimensionless friction power (**d**) Average temperature rise (**e**) Dimensionless principal stiffness (**f**) Dimensionless principal damping.  
increases, so the bearing load capacity gradually increases. When it is increased to a certain range, the pumping effect is the best, and then the bearing load capacity gradually decreases. The Figure 16 shows that the helix angle has a more obvious influence on the bearing load capacity of the convergent HGJBs than that of the constant-width HGJBs. When the helix angle is 30\({}^{\circ}\), the pumping effect of the convergent HGJBs reaches its best result, which is nearly twice the bearing load capacity corresponding to the helix angle of 45\({}^{\circ}\) when the eccentricity is 0.7. Similarly, when the helix angle is 30\({}^{\circ}\), the bearing load capacity of the constant-width HGJBs is the largest, and when the eccentricity is 0.5, it is only half of the maximum bearing load capacity of the convergent HGJBs. The side leakage increases with the increase of the helix angle of the HGJBs. When the helix angle is 75\({}^{\circ}\), the corresponding side leakage of the convergent HGJBs is nearly five times that when the helix angle is 15\({}^{\circ}\). As the helix angle increases, the friction power of the convergent HGJBs also increases, but the amount of change is not obvious, and the increase is not large. Due to the increase of the side leakage, the helix angle increases, and the temperature rise decreases. When the helix angle increases from 15\({}^{\circ}\) to 75\({}^{\circ}\), the average temperature rise drops significantly, overall, about 5 \({}^{\circ}\)C.  
With the increase of the helix angle, the stiffness coefficient and damping coefficient of the bearing gradually increase, and the growth rate decreases with the increase of the helix angle. When the helix angle is small, the stability of the bearing is poor. The stiffness coefficient of the convergence HGJBs basically remains stable after the helix angle of 45\({}^{\circ}\). When the eccentricity is 0.5, the stiffness coefficient corresponding to the helix angle of 75\({}^{\circ}\) is basically the same as the stiffness coefficient corresponding to the helix angle of 45\({}^{\circ}\).  
Considering the bearing load capacity and stability factors, the helix angle of the convergent HGJBs is 30\({}^{\circ}\)-45\({}^{\circ}\), and the helix angle of the constant-width HGJBs is 30\({}^{\circ}\)-45\({}^{\circ}\). At this time, the bearing performance is the best.