Design of Jet Control Device for Forced Lubrication System of Bearing

In response to the problem of poor lubrication effect and unstable bearing operation leading to bearing failure in traditional bearings, the solution of installing a jet device on the bearing has been proposed. Using numerical calculation software, analyze the impact of installing a semi-circular or 1/4 circular jet device on the temperature field and leakage rate of the bearing. The results show that after installing a jet control device, the temperature of the flow field around the bearing decreases significantly at the same inlet pressure, while the leakage rate decreases. Keeping the speed and oil temperature constant, as the pressure at the lubricating oil inlet increases, the leakage rate decreases by 51.87% -59.80%; Keeping the rotational speed and oil inlet pressure unchanged, as the temperature of the lubricating oil at the inlet increases, the leakage decreases by 45.94% -50.74%; Keeping the inlet pressure and oil temperature unchanged, when the speed increases, the leakage decreases by 12.58% -18.31%. Install a jet device on the end face of the bearing to achieve collaborative design of low leakage and low temperature rise at the bearing, thus providing a theoretical basis for the long-term design of the bearing.


Introduction
At present, aviation engines have tended towards lightweight and integrated structures to achieve goals such as high thrust to weight ratio, low fuel consumption, and long service life [1,2].As one of the key components, the requirements for bearings have become increasingly stringent.For example, the DN value of aviation engine spindle bearings can reach 3×10 6 or above [3][4][5], and the thrust ball bearings can withstand a load of 45000N [6].As the main fuel injection method for high-speed systems such as gas turbine engines [7], fuel injection lubrication is mainly based on the principle of spraying lubricating oil onto the friction surface at high speed through a nozzle, forming a lubricating film, thereby reducing friction and wear, and extending bearing life.Therefore, the operating status of bearings depends on their lubrication performance and mechanical characteristics.If the lubrication effect of bearings is poor, unstable operation of bearings will lead to bearing failure, which will lead to increased vibration, noise, and energy consumption of the system, and may even lead to operational failures of the entire system.Therefore, optimizing the lubrication design of the bearing itself to meet 2 the operational requirements of the system is crucial for the performance and reliability of the entire system [8].
Scholars at home and abroad have conducted extensive research on oil injection lubrication of bearings.Panel et al. [9] conducted an experimental study on diagonal contact ball bearings with DN values of 2.5×10 6 to explore the lubrication effect of oil injection.Experiments have shown that jet lubrication can significantly reduce bearing temperature, but cause large power loss.Zheng et al. [10] explored the effect of oil supply parameters on the performance of double half inner ring angular contact ball bearings in their study.The results indicate that the flow rate and injection angle of spray lubrication have the most significant effects on bearing temperature rise and system power consumption, while the effects of pressure and injection aperture on bearing performance are relatively small.Wang et al. [11] mainly discussed the deviation of nozzle injection direction in lubrication systems.And it is concluded that in practical applications, by adjusting the nozzle parameters and the position and angle with the injection hole, the deviation in the injection direction can be reduced, thereby improving the efficiency and performance of the injection lubrication system.Yan et al. [12] used ANSYS software to investigate the fuel injection diffusion characteristics of nozzles with different shapes at different Reynolds numbers.The results show that regardless of the shape of the nozzle, the axial injection speed shows a trend of increasing first and then decreasing, and the shape of the injection flow part is consistent with the shape of the nozzle itself.In addition, as the axial position increases, the fuel injection will gradually become rounded.Xu et al. [13] conducted transient simulation analysis of gas-liquid two-phase flow in rolling bearings.Using VOF model and sliding grid technology to obtain results that conform to physical facts.Research has found that the pressure at the lubricating oil film is the highest, and the volume fraction of liquid oil in the bearing varies with speed and oil supply, and there is an optimal oil supply at different speeds.Researchers such as Liu and Wang [14] conducted a study on the penetration mechanism of bearing lubricating oil through oil injection lubrication under high DN value conditions based on aerodynamics.The results of research calculations indicate that when the small end face of the bearing is close to the inner race, lubricating oil is more likely to enter the bearing.When the bearing speed is low, increasing the oil supply can effectively increase the volume fraction of oil in the bearing.However, when the speed is high, increasing the oil delivery rate does not significantly increase the volume percentage of oil in the bearing.Shen et al. [15] used fluent fluid calculation software to simulate and analyze the oil injection lubrication infiltration process between bearing rings.Research has found that as the rotational speed increases, the proportion of large particle oil in the bearing chamber gradually decreases, thereby affecting the lubrication effect of the bearing.
For the oil injection lubrication of bearings, many scholars mainly focus on the nozzle direction and oil injection flow rate, but the above methods will greatly increase the use of lubricating oil while ensuring bearing lubrication.However, under complex operating conditions such as high speed, high temperature, and high pressure, it is urgently necessary to conduct research on bearing jet control in order to reduce the use of lubricating oil and seal face pressure while ensuring bearing lubrication.This article uses theoretical and numerical simulation software to install a jet control device on the inner ring of the bearing, in order to reduce the use of lubricating oil, reduce bearing temperature, and improve bearing life, providing a theoretical basis for improving the actual lubrication state of the bearing.

Deep Groove Ball Bearing Model
The research object of this article is deep groove ball bearing, as shown in figure 1.The structural parameters of the bearing are shown in table 1.In order to facilitate modelling, mesh generation, and subsequent calculations, the model is simplified: (1) Do not consider the chamfering of the inner and outer rings of the bearing and keep the cage flat;

Bearing Fluid Domain Model
Due to the consideration of the impact of the internal jet device on bearing heat dissipation and the changes in bearing leakage after installing the jet device, therefore, using Creo software to model the fluid domain of bearing, forming a lubricating oil film around the ball and leaving an overhead gap, as shown in figure 2 and figure 3.           From the comparison of numerical calculation results and cloud maps, it can be seen that compared to the original bearing flow field, when 3 or 5 jet control devices are installed, the overall temperature of the bearing decreases during operation.Some lubricating oil passes through the ball and is then turned back by the jet control device, lubricating the bearing to reduce its temperature.However, by comparing the installation of a full circle jet control device, it can be found that when too many jet control devices are installed at the outlet, the lubricating oil that should have flowed out from the outlet cannot flow out normally, and can only flow out from the fluid inlet side through the ball again.Although this reduces the experimental amount of lubricating oil and allows all lubricating oil to undergo secondary lubrication, it causes the lubricating oil to stay in the raceway for a long time and cannot flow out, The continuous temperature rise caused by ball friction causes it to heat up, but the inability to quickly flow out also prevents the lubricating oil from quickly taking away heat, resulting in poor lubrication effect when installing a full cycle jet control device.Therefore, it can be inferred that when installing a jet control device, some space needs to be left as a quick outlet for lubricating oil to take away heat.

Effect of Installing a 1/4 Arc Jet Device on Bearing Temperature
The structure of the variable jet control device is used to maintain the basic working conditions of a fluid inlet of 200 kPa, a rotational speed of 100 rpm, and an outlet pressure of standard atmospheric pressure.The cloud map of the bearing fluid domain under the 1⁄4 arc jet control device is compared with the cloud map of the bearing fluid domain under the semi-circular arc jet control device.The results are shown in figures 12, 13, and 14.By comparing the above temperature cloud maps, it can be seen that among the three and five jet devices installed, the semi-circular arc jet control device improves lubrication better than the 1⁄4 arc jet control device.Because the semi-circular arc jet control device directly flows lubricating oil back to the ball, allowing it to directly perform secondary lubrication on the bearing, the effect is good.However, the 1/4 arc jet control device mostly directly flows out of the jet control device when refluxing the lubricating oil, with only a small portion being able to flow back to the ball, resulting in poor lubrication effect.
However, compared to the semi-circular arc jet control device, the 1 ⁄ 4 circular arc jet control device performs better than the semi-circular arc jet control device when installed throughout the entire circumference, because the lubricating oil of the 1⁄4 circular arc jet control device can flow out from the outlet, and the lubricating oil does not need to flow back to the inlet side to flow out again, allowing it to quickly flow out and take away heat.

Bearing Leakage Model
To facilitate modelling and simulation, the leakage end model was simplified to a thin circular wall.The fluid domain modelling and inlet and outlet settings in the bearing cavity are shown in figure 15.The results after 3D mesh division are shown in figure 16.

Impact of Jet Device on Bearing Leakage
Install a jet control device on the bearing and compare the fluid conditions at a speed of 100 rpm and a pressure of 100 kPa and 1000 kPa, respectively.The results are shown in figures 17-20.Using CFD Post software for post-processing, a fluid streamline diagram was obtained.From the diagram, it can be seen that when the lubricating oil flows through the bearing and is partially blocked by the jet control device, the mass flow data at the leakage channel was obtained using the function calculator function of CFD Post as shown in table 2. According to the mass flow data at the leakage end, it can be seen that after installing a jet control device, the leakage of lubricating oil is significantly reduced, and the leakage of bearings with jet control devices is reduced by about 51.87% -59.80% compared to traditional bearings.And as the oil pressure at the inlet increases, the amount of lubricating oil leaking from the leaking end per second decreases more significantly.According to the mass flow data at the leakage end, it can be seen that under different temperatures, the jet lubrication device can reliably and effectively reflux some lubricating oil.The bearings equipped with jet devices reduce the leakage amount by about 45.94% -50.74% compared to traditional bearings.From the mass flow data of the leakage end, it can be seen that under different rotational speeds, the leakage of bearings equipped with a jet device is reduced by about 12.58% -18.31% compared to traditional bearings.The jet lubrication device can reliably and effectively reflux some lubricating oil, achieving the goal of reducing lubricating oil leakage.

Conclusion
(1) As the outlet pressure of the nozzle increases, the fuel injection speed increases significantly.However, due to the smaller diameter of the nozzle, it only causes an increase in the flow rate of the fluid around the bearing, which increases the temperature and velocity, but does not have a significant impact on the fluid in the bearing cavity.The jet lubrication pressure should not be too low.If it is too low, the fluid speed will be too slow, which will not have sufficient lubrication effect on the bearing.It is necessary to maintain a certain pressure to allow it to pass through the bearing.
(2) When installing a bearing jet control device, it is not advisable to completely cover the opposite side of the jet, as this can cause excessive lubricating oil back flow and insufficient cooling effect.
(3) When using jet lubrication, after installing a jet control device, the temperature of the flow field around the bearing decreases significantly at the same inlet pressure, while the leakage rate decreases.When the speed is low, as the pressure at the lubricating oil inlet increases, the leakage rate decreases by 51.87% -59.80%%;When the speed is low, as the temperature of the lubricating oil at the inlet increases, the leakage decreases by 45.94% -50.74%;When the speed is high, the leakage decreases by 12.58% -18.31%.

Figure 3 .
Figure 2. Bearing fluid domain model.Figure 3. Bearing fluid domain grid division.2.3.Mesh Division of Fluid Domain in the Inner Cavity of Bearing Seat Use Creo software to model the internal fluid domain of the bearing seat, as shown in figure 4. The lubricating oil fluid entry channel on the left was established, a fluid entry and exit channel on the right and bottom, and the middle is the fluid area for bearing lubrication and the disordered lubricating oil flow area in the bearing seat cavity.After the model was established, use ANSYS messaging software to divide the tetrahedral mesh of the established fluid model in the bearing seat cavity, as

Figure 4 .
Figure 4. Fluid domain model of bearing seat inner cavity.

Figure 5 .
Figure 5. Mesh division of fluid domain in the inner cavity of 1.5 bearing seat.

Figure 6 .
Figure 6.Solid modelling of adding a semicircular arc jet device.

3. 2 .
Impact of Installing a Semi-Circular Arc Jet Device on Bearing Temperature Keeping the initial inlet pressure of the fluid at 200 kPa, the rotational speed at 100 rpm, and the outlet pressure at standard atmospheric pressure unchanged, first perform numerical simulation on the semicircular arc jet control device.Install 3, 5, and a full circle semi-circular arc jet control device at the outlet of the bearing fluid domain, and use Ansys fluent software for simulation.By comparing the cloud map, obtain a more reasonable number of installations under the premise of the semi-circular arc jet control device, The results are shown in figures 8, 9, 10, and 11.

Figure 8 .
Figure 8. Cloud simulation of the original flow field of the bearing.

Figure 9 .
Figure 9. Cloud chart of flow field simulation for three semi-circular arc jet control devices installed in bearings.

Figure 10 .
Figure 10.Cloud chart of flow field simulation for five semi-circular arc jet control devices installed in bearings.

Figure 11 .
Figure 11.Cloud chart of flow field simulation for the installation of full circle arc jet control device in bearings.

Figure 12 .
Figure 12.Cloud chart of flow field simulation for three 1⁄4 arc jet control devices installed in bearings.

Figure 13 .
Figure 13.Cloud chart of flow field simulation for five 1 ⁄ 4 arc jet control devices installed on bearings.

Figure 14 .
Figure 14.Cloud chart of flow field simulation for a 1⁄4 arc jet control device installed on a bearing.

Figure 15 .
Figure 15.Fluid domain model in bearing cavity.Figure 16.Mesh division of fluid domain model in bearing cavity.

Figure 17 .
Figure 17.Fluid situation at a speed of 100 rpm and a pressure of 100 kPa.

Figure 18 .
Figure 18.Fluid situation after installing a jet control device at a speed of 100 rpm and a pressure of 100 kPa.

Figure 20 .
Figure 20.Fluid situation after installing a jet control device at a speed of 100 rpm and a pressure of 1000 kPa.

4. 3 .
The Influence of Oil Temperature on the Leakage Rate of Bearings Equipped with Jet Devices Next, numerical simulations will be conducted on the fluid domain at different speeds and temperatures to test whether the jet control device is still reliable at different speeds and temperatures.Firstly, select the operating conditions of 100 rpm and 100 kPa, and the numerical simulation results of the fluid domain at different temperatures are shown in figures 21-24.

Figure 21 .
Figure 21.Fluid situation at a speed of 100 rpm, pressure of 100 kPa, and temperature of 30 ℃.

Figure 22 .
Figure 22.Fluid situation with jet control device installed at a speed of 100 rpm, pressure of 100 kPa, and temperature of 30 ℃.

Figure 23 .
Figure 23.Fluid situation at a speed of 100 rpm, pressure of 100 kPa, and temperature of 40 ℃.

Figure 24 .
Figure 24.Fluid situation with jet control device installed at a speed of 100 rpm, pressure of 100 kPa, and temperature of 40 ℃.The mass flow data at the leakage channel obtained using CFD Post is shown in table 3.

4. 4 .
The Influence of Rotational Speed on the Leakage Rate of Bearings Equipped with Jet Devices Perform numerical simulations on fluid domains at different rotational speeds to test whether the jet control device remains reliable at different rotational speeds.Firstly, select the operating conditions of 100 kPa and 50 ℃, and the numerical simulation results of the fluid domain at different speeds are shown in figures 25-28.

Figure 26 .
Figure 26.Fluid situation with jet control device installed at a speed of 1000 rpm, pressure of 100 kPa, and temperature of 50 ℃.

Figure 28 .
Figure 28.Fluid situation with jet control device installed at a speed of 1500 rpm, pressure of 100 kPa, and temperature of 50 ℃.

Table 1 .
Structural parameters of bearings.

Table 2 .
Mass flow data of leakage ends under different pressures.

Table 3 .
Leakage mass flow data at different temperatures.

Table 4 .
Leakage mass flow data at different rotational speeds.