Water-Lubricated Bearings are essential parts of ships and submarines. They support the heavy propeller shaft. Unlike standard bearings, they use water instead of oil. This is good for the environment because water is clean. However, water is very thin compared to oil. This causes engineering challenges. The thin water film often allows the metal shaft to touch the rubber bearing. This contact creates friction and heat. The heat makes the materials expand. To solve this, engineers must use Thermal FSI simulation. This stands for Fluid-Structure Interaction. We use ANSYS Fluent to calculate the water flow and ANSYS Mechanical to calculate the shape change. This CFD Analysis of Water-Lubricated Bearing helps us predict reliability and prevent overheating.

In this ANSYS Fluent tutorial, you will learn how to perform a detailed Thermal FSI simulation. We teach you how to set up 2-way FSI Coupling to connect the fluid and solid solvers. By watching this training, you will understand how pressure changes the bearing shape and how heat moves through the system. For more lessons on coupled simulations, please explore our Fluid-structure interaction tutorials.

• Reference [1]: Han, Yanfeng, et al. “A fluid–solid–heat coupling analysis for water-lubricated rubber stern bearing considering the deflection of propeller shaft.” Applied Sciences 11.3 (2021): 1170.

Figure 1: Schematic of water-lubricated rubber stern bearing [1]

Simulation process: 2-Way FSI Coupling and Model Setup in ANSYS

In this Fluent simulation tutorial, we guide you through designing a realistic geometry based on a marine stern tube. The system includes a steel shaft with a 90 mm diameter and a rubber bearing liner. The liner has 8 grooves to let water flow through. You will learn to create a detailed mesh for both parts. The fluid mesh is fine near the walls to capture the thin boundary layer. The solid mesh focuses on the inner rubber surface. We use ANSYS System Coupling to connect the solvers. ANSYS Fluent solves the fluid flow and heat transfer in the thin water gap. The Coupled Field Static solver calculates the structural deformation and thermal expansion.

We demonstrate how to set up the FSI Coupling ANSYS to be 2-way. This means Fluent sends pressure data to Mechanical. Then, Mechanical sends the new deformed shape back to Fluent. We applied a 10 kN external load to the shaft to simulate the propeller weight. The rotation speed creates viscous heating in the water. We assigned a convection boundary condition to the outer wall to simulate cooling by seawater. The simulation iterates until the pressure and deformation are balanced. This ensures your Fluid-structure interaction Fluent simulation is accurate and physically correct.

Figure 2: Computational Mesh grid of the Water-Lubricated Bearing showing the solid rubber liner with 8 axial grooves.

Post-processing: Thermal FSI Analysis of Thermo-Hydrodynamic Performance

This section of the tutorial analyzes the engineering data to evaluate the bearing safety. We examine the pressure, deformation, and temperature to understand the complex interaction. First, we analyze the Pressure Contours in Figure 3. The CFD simulation calculates a Maximum Pressure of 1005 Pa. This red zone is located at the bottom of the bearing. This happens because the 10 kN load pushes the shaft down. This creates a converging wedge shape. The water gets squeezed into this small gap, which generates the pressure to lift the shaft. We also see a Negative Pressure of -126 Pa. This indicates a risk of cavitation, where water turns into vapor bubbles. By learning to identify these zones, you can place grooves correctly to avoid damage.

Next, we look at the Total Deformation in Figure 5. The Maximum Deformation is 5.45×10⁻⁵ m (about 0.055 mm). This is a very critical finding in our ANSYS analysis. The original gap between the shaft and bearing is only 0.15 mm. This means the rubber deformation takes up more than 30% of the clearance. If we did not use 2-way FSI Coupling, we would miss this effect. The pressure pushes the soft rubber outward. This changes the water film thickness. This result proves that rigid-body simulations are not accurate for Water-Lubricated Bearings. The manufacturer must use a harder rubber or change the gap size to account for this deformation.

Figure 3: Static Pressure Contours on the bearing inner surface, highlighting the high-pressure load-carrying zone at the bottom and low-pressure regions at the top.

Figure 4: Temperature Contours across the bearing cross-section, visualizing the heat generation at the shaft interface and cooling near the outer wall.

Figure 5: Total Deformation Contours of the rubber liner, showing the structural displacement caused by the hydrodynamic water pressure and shaft load.

Finally, we evaluate the Temperature Distribution in Figure 4 and the Data Table. The table shows a Maximum Temperature of 32.86°C. The heat is generated at the shaft surface due to friction. The outer surface is cooler at 20°C. The limit for rubber material is usually 60°C. Therefore, our Fluent simulation confirms that the cooling grooves are effective. The heat flows from the water, through the rubber, to the sea. Additionally, the table highlights a Maximum Stress of 10,435 Pa, which confirms the mechanical load on the liner is within safe limits.