Studying how fish swim helps engineers build better underwater robots. A Wavy Foil CFD simulation is a computer model that copies this swimming motion. This work is a key part of biomimicry, where we learn from nature’s perfect designs. Using a Dynamic Mesh For Wavy Foil Fluent analysis, we can see the exact water patterns that create forward push, or thrust generation. This is an unsteady CFD simulation because the flow changes constantly as the foil moves. We use ANSYS Fluent with a special User-Defined Function (UDF) to control the foil’s movement. This Dynamic Mesh CFD study validates our model against the research paper, “Characteristics of flow over traveling wavy foils in a side-by-side arrangement” [1], proving our ability to analyze the complex hydrodynamics of swimming.

• Reference [1]: Dong, Gen-Jin, and Xi-Yun Lu. “Characteristics of flow over traveling wavy foils in a side-by-side arrangement.” Physics of fluids5 (2007).

Figure 1: Schematic of the configuration used for the Fish Swimming Hydrodynamics analysis, based on the reference paper [1].

Simulation Process: Fluent Setup, UDF-Driven Dynamic Mesh for Wavy Motion

To perform this mesh deformation analysis, we first designed the wavy foil geometry based on the reference paper [1]. We then created a high-quality mesh of 36,356 cells, with smaller cells placed very close to the foil to capture the flow details accurately. The key to this simulation is making the rigid foil move in a wave-like pattern. To do this, we wrote a special code called a User-Defined Function (UDF). This UDF tells ANSYS Fluent the exact mathematical formula for the swimming motion. The Dynamic Mesh feature then uses the “Smoothing” method to stretch and deform the grid to follow the foil’s movement. This method is very efficient and saves computer time.

Figure 2: A view of the dynamic mesh generation, showing the grid deformation during the Wavy Foil Fluent simulation.

Post-processing: CFD Analysis, Thrust Generation and Vortex Dynamics

The pressure contour provides a professional visual that acts as a map of the forces on the foil. This professional visual reveals alternating zones of high and low pressure that travel along the foil’s body as it undulates. The pressure fluctuates between -207 Pa and 630 Pa. This pressure difference between the front and back of each wave on the foil is the direct source of the forward push, or thrust. The simulation allows us to see precisely how this propulsive force is generated at every moment in time, showing that the largest push comes from the areas with the biggest curve.

Figure 3: A professional visual of the pressure distribution from the Thrust Generation CFD analysis.

The velocity contour tells the final story of how the foil transfers energy to the water to move forward. This professional visual shows jets of water being pushed backward at speeds up to 2.1 m/s. By Newton’s third law, pushing water backward propels the foil forward. More importantly, the simulation reveals a special zigzag pattern of spinning water, or vortices, being shed behind the foil. This “reverse von Kármán vortex street” is the clear signature of an object producing thrust, not drag. It is proof that the wavy motion is working efficiently. The most important achievement of this simulation is the clear, visual proof that the UDF-driven dynamic mesh model can accurately capture the coupled physics of how a specific wavy motion creates a pressure differential for thrust and sheds a propulsive vortex wake, giving engineers a powerful tool to design more efficient underwater vehicles.

Figure 4: Velocity magnitude from the Vortex Shedding Fluent simulation, showing the thrust-producing wake pattern.