Sloshing Oil FSI CFD Simulation: ANSYS Fluent Tutorial

Driving a massive oil tanker truck down the highway is incredibly dangerous. When the driver hits the brakes, the heavy liquid inside the tank does not simply stop moving. Its massive momentum carries it forward, causing it to crash violently against the front metal walls. This powerful internal wave action is known as oil sloshing. The heavy fluid acts like a hammer, and if the impact force is too high, the metal tank can easily bend, crack, or even flip the entire truck over.

The objective of this project is to use ANSYS Fluent and Mechanical coupling to predict the oil sloshing wave impacts and calculate the resulting structural deformation of the tank walls. By understanding how the fluid crashes into the metal, engineers can design stronger internal walls to keep the truck safe on the road.

Figure 1: The 3D geometry of the commercial oil tanker used to study violent fluid motion.

Simulation Process: Volume of Fluid and 2-Way FSI Setup

To model this chaotic event, we build a complete 3D computational model of the tanker shell and its internal support baffles. We rely on the Volume of Fluid (VOF) multiphase model inside Fluent. This specific mathematical tool tracks exactly where the empty air ends and the heavy oil begins. But modeling the fluid alone is not enough. When the heavy oil hits the metal, the metal physically stretches. As the wall stretches and changes shape, it alters how the fluid flows immediately after. We must capture this continuous feedback loop. To do this, we use a 2-way fluid-structure interaction method. Fluent calculates the heavy fluid pressure and sends it directly to the ANSYS Mechanical solver. The mechanical solver bends the metal walls under that pressure, and then it feeds the newly bent shape back into the fluid solver.

Because the physical walls are moving, the fluid mesh inside must stretch to match it. We activate dynamic mesh smoothing to let the grid flex without crashing the calculation. Learning this data exchange process is a critical skill found in modern fluid-structure interaction tutorials.

Figure 2: The internal tank geometry revealing the structural baffles designed to slow down the moving fluid.

Post-processing: Wave Formation, Deformation, and Elastic Strain

We carefully evaluate the structural safety of the tanker by analyzing the fluid wave shapes, the total deformation contours, and the internal mechanical strain. To start, we look at the root cause of the physical danger. We examine the oil volume fraction contour at exactly 1.5 s into the simulated sudden stop. At this precise moment, a massive, unbalanced wave forms inside the tank. The fluid piles up heavily against one side, reaching a peak volume fraction of 0.970 in the dark green zones. The air is violently pushed away. This massive wall of oil delivers a huge, unbalanced impact load directly onto the structure.

This impact forces the metal to react. We analyze the total deformation contour to see the damage. The mechanical solver proves that the highest amount of physical bending happens right at the rounded ends of the tank, exactly where the fluid hits the hardest. The metal wall pushes outward, reaching a maximum total deformation of 3.8164e-7 m. While this bending distance is physically tiny, repeated stretching over thousands of stops can cause severe metal fatigue.

Figure 3: The total deformation map showing the metal pushing outward at the ends due to the heavy fluid impact.

Figure 4: The equivalent elastic strain distribution, highlighting stress concentrations at the lower support joints.

At last, we should check if this bending will tear the tank apart. We evaluate the equivalent elastic strain. The fluid hits the main walls, but the twisting force travels downward into the lower support mounts. The strain contour shows small red hotspots at the connections between the tank wall and the internal supports. The material stretches to a maximum strain of 7.861e-7 m/m, dropping to a minimum of 4.11e-9 m/m in the safer blue regions. Most importantly, the structural solver calculates a maximum peak stress of 1.5637e5 Pa. This number is the ultimate proof of safety. This specific stress level sits far below the breaking point of industrial structural steel. The 2-way analysis confirms that while the sloshing oil hits hard, the tank design is completely safe.

Figure 5:  The oil volume fraction contour at 1.5 s, capturing the unbalanced fluid wave piling up on one side.

FAQ About Oil Sloshing FSI CFD Simulation

• Why do we use the VOF model for sloshing analysis?
• The Volume of Fluid (VOF) model is specifically designed to track the clear boundary between two different fluids. In this project, it perfectly maps the sharp dividing line between the empty air and the moving oil.
• What happens to the fluid at 1.5 s into the simulation?
• The sudden movement forces the liquid to surge forward. At 1.5 s, the oil violently piles up against one side of the tank, reaching a volume fraction of 0.970 and acting like a heavy hammer against the wall.
• Is this oil tanker design safe against structural failure?
• Yes. Even under a heavy sloshing impact, the maximum structural stress only reaches 1.5637e5 Pa. Because this pressure is much lower than the yield strength of the steel, the tank will not crack.