The rapid development of gasoline turbochargers has enabled these systems to operate in increasingly harsh environments, including high temperatures, high speeds, and high pressures. These extreme conditions can cause the lubricant to degrade, leading to carbon deposits on the seal ring and a loss of elasticity. To ensure the proper functioning of the floating bearing and the sealing ring, it is generally recommended that the temperature at the turbine end’s floating bearing portion does not exceed 150°C, and the temperature at the seal ring remains below 230°C. This paper presents a fluid-solid coupling analysis and steady-state thermal simulation of a water-cooled bearing body to determine the temperature distribution across the component. The goal is to evaluate the design of the coolant channels and verify whether the size of the coolant inlet flow is adequate. This research provides a practical approach for the development of bearing body designs.
**Fundamental**
1. **Calculation Model Analysis**
The fluids involved in the simulation include engine coolant and lubricating oil, while the solid structure is the bearing body. These two fluids do not mix or interact directly, and their movement does not cause significant deformation of the bearing body. However, they do influence each other’s flow patterns. This represents a unidirectional coupling problem where heat exchange occurs between the fluid and the solid. There is mutual interaction between the fluid and the solid wall, and the thermal boundary conditions are not known beforehand. This is a typical weak coupling scenario, where the temperature and heat transfer coefficient at the boundary are calculated as part of the solution, rather than being predefined. A more effective method to solve this is to perform a fluid-solid coupling analysis, which allows accurate modeling of heat transfer between the fluid and the solid wall.
2. **Heat Transfer Theory**
When fluid flows within the bearing body cavity, a boundary layer forms near the wall surface, where the fluid velocity is very low, almost zero. In this region, heat exchange primarily occurs through conduction. Outside the boundary layer, heat transfer is mainly convective. The heat transfer due to conduction can be described by Fourier’s Law:
$$ q = -\lambda \frac{dT}{dx} $$
Where $ q $ is the heat flux, $ \lambda $ is the thermal conductivity, and $ \frac{dT}{dx} $ is the temperature gradient.
For convective heat transfer, Newton's Law of Cooling is used:
$$ q = h (T_w - T_f) $$
Where $ h $ is the heat transfer coefficient, $ T_w $ is the wall temperature, and $ T_f $ is the fluid temperature.
From energy conservation, the heat released by the fluid equals the heat absorbed by the solid at the boundary, which leads to the following equation:
$$ \lambda \frac{dT}{dx} = h (T_w - T_f) $$
This relationship ensures consistency between the thermal behavior of the fluid and the solid during the simulation.
**Establishment of a Computational Model**
This study focuses on analyzing the temperature field distribution of the bearing body under the influence of both coolant and lubricating oil. To reduce computational time and resource usage, the actual fluid domains (coolant and lubricating oil) are not included in the model. Instead, the temperature at the interface between these regions and the bearing body is obtained through experimental testing and prior calculations, and then applied as a boundary condition. Heat exchange between the turbine casing and the bearing body occurs via conduction, and the outer surface of the bearing body also exchanges heat with the surrounding air.
1. **Geometric Model Processing**
A three-dimensional model of a gasoline engine supercharger developed by our company was selected for this study. The bearing body uses water circulation cooling, and in addition to lubricating the floating bearing, the lubricating oil also helps dissipate heat. The 3D model includes three main parts: the bearing body, the cooling water channel, and the lubricating oil passage. The bearing body model was created in UG, and non-critical features such as chamfers and positioning holes were simplified to improve mesh quality. The fluid models were generated based on the bearing body geometry and further simplified to enhance computational efficiency.
2. **Meshing of the Computational Model**
The bearing body was meshed using a tetrahedral mesh in ANSYS, with local refinement applied to areas of interest. For the fluid domains—cooling water and lubricating oil—the mesh was generated as CFD grids, with special attention given to the boundary layers. The resulting grid models are shown in Figures 1, 2, and 3.
**Calculation Results**
In CFX, a fluid-solid coupling simulation was performed, treating the two fluid domains separately from the bearing body. This allowed the calculation of the surface temperature and convective heat transfer coefficient of each fluid. These values were then applied as boundary conditions in a steady-state thermal analysis of the bearing body, enabling the determination of its overall temperature distribution. The results for the two fluid domains are presented in Figures 4 and 5, while Figure 6 shows the temperature distribution of the bearing body.
**Conclusion**
The calculated temperature distribution aligns well with experimental results, confirming the feasibility of the analytical method used in this study. From the cloud data obtained, the temperatures near the floating bearing and the seal ring remain below the allowable limits, indicating that the cooling design of the bearing body is effective and suitable for real-world applications.
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