# Analysis of Grinding Flow Field under Minimum Quantity Lubrication Condition
## 3 Simulation and Analysis of Three-Dimensional Grinding Wheel Flow Field
### Simulation and Analysis of the Grinding Wheel Flow Field under MQL Conditions
#### 3.3.2 Effect of MQL Jet on the Flow Field of the Grinding Wheel  
The effect of the MQL jet on the flow field of the grinding wheel is not conducive to the grinding fluid entering the grinding zone. However, the small droplets produced by atomization of grinding fluid have certain kinetic energy and can overcome the obstruction of the grinding wheel flow field to enter the grinding zone. Since the grinding fluid density is certain, the droplet kinetic energy is determined by the initial velocity of the droplet and the droplet volume. According to the spray principle, the grinding fluid flow rate and the compressed gas pressure are the key factors affecting the droplet volume and velocity.  
1. Effect of Grinding Fluid Flow on Effective Flow Rate  
When the grinding wheel linear velocity was 40 m/s and the compressed gas pressure was 6 bar, the grinding fluid flow rates were taken as 54.11 mL/h, 66.41 mL/h and 77.17 mL/h. The trajectory diagrams of droplet motion at three flow rates were obtained,  
Figure 11: Local enlargement of the velocity vector in the wedge region.  
Figure 10: Flow field simulation geometry model.  
which were illustrated by Figure 13. It was found that the effective flow rate of the grinding fluid into the grinding zone did not differ much under the three flow rate conditions. The reason is that the variation in the grinding fluid flow rate is too small, only about 10 mL/h, which has a small effect on the volume and velocity of the droplets. The kinetic energy of the droplets did not change much under the three conditions.  
2. Effect of the grinding wheel linear velocity on effective flow rate  
When the grinding fluid flow rate was taken as 77.17 mL/h and the compressed gas pressure was 6 bar, the grinding wheel linear speed was set to 20 m/s, 25 m/s, 30 m/s, 35 m/s and 40 m/s for fluid simulation. The results are shown in Figure 14. It can be found that when the linear velocity is less than 30 m/s, due to the air barrier layer, the grinding fluid flowing out of the grinding area decreases as the linear velocity of the grinding wheel increases, i.e., the effective flow rate increases. When the linear velocity is greater than 30 m/s, the effective flow rate of grinding fluid lowers as the linear velocity of the grinding wheel raises. This is due to the weak strength of the air barrier layer when the linear velocity is low. The grinding fluid droplets still have high velocity after passing through the air barrier layer and break into small droplets on the workpiece surface and grinding wheel. The effective flow rate increases. As the linear velocity increases, the airflow field obstruction increases. When the grinding wheel linear velocity exceeds 30 m/s, the obstructing effect of the air barrier increases, the velocity of grinding fluid droplets lowers, and the droplets number that collide and splash decreases. The power of the grinding fluid droplets to pass through the air barrier is reduced, resulting in a lower effective flow rate into the grinding zone.  
3. Effect of the compressed gas pressure on effective flow rate of the grinding fluid  
When the grinding wheel linear velocity was 40 m/s and the grinding fluid flow rate was 77.17 mL/h, the motion trajectories of the grinding fluid droplets under the different pressure conditions were obtained by varying the compressed gas pressure. The values of compressed gas pressure were taken as 2 bar, 4 bar and 6 bar. The motion trajectory diagrams of the extracted droplets in the whole calculation domain are shown in Figure 15a-c.  
Figure 12: Pressure distribution of flow field.  
Figure 13: Droplet trajectory under the different grinding fluid flow. (a) Q = 54.11 mL/h\({}_{2}\) (b) Q = 66.41 mL/h; (c) Q = 77.17 mL/h.  
Figure 14: Droplet trajectory under the different grinding wheel linear velocity. (**a**) \(v_{\rm s}=20\) m/s; (**b**) \(v_{\rm s}=25\) m/s; (**c**) \(v_{\rm s}=30\) m/s; (**d**) \(v_{\rm s}=35\) m/s.  
Figure 15: _Cont._