Nature often holds the key to solving complex engineering problems. One of the best examples is the humpback whale. Despite its massive size, it is incredibly agile thanks to bumpy structures on the front of its flippers called tubercles. Engineers have applied this concept to wind turbine blades to solve the problem of “stall,” where air separates from the blade and reduces power.

This project is a Leading Edge Tubercle CFD simulation designed to investigate this bio-mimetic phenomenon. This is a CFD study that explores how these bumps change the airflow to improve performance. We use ANSYS Fluent to model the flow physics and visualize the benefits of this design. For those new to the basics of flow behavior, we recommend starting with our fluid mechanics tutorials. Our simulation setup is inspired by the impactful research published in Energy Conversion and Management [1].

• Reference [1]: Joseph, Jeena, and A. Sathyabhama. “Leading edge tubercle on wind turbine blade to mitigate problems of stall, hysteresis, and laminar separation bubble.” Energy Conversion and Management255 (2022): 115337.

Figure 1: Comparison of a standard baseline blade and the bio-inspired Leading Edge Tubercle blade [1].

Simulation Process: Modeling the Wavy Airfoil in Fluent

To perform this Leading Edge Tubercle fluent simulation, we first created the unique geometry. Unlike a smooth wing, the leading edge of this airfoil has a sinusoidal, wavy pattern that mimics the whale’s flipper. We placed this blade inside a large computational domain to ensure we could capture the full behavior of the air flowing behind it. We then generated a very fine mesh consisting of 4,031,516 cells. A mesh of this high density is absolutely necessary to resolve the tiny, complex flow structures that form around the bumps.

In the ANSYS Fluent setup, we selected the k-omega SST turbulence model. This specific model is the industry standard for aerodynamics because it is excellent at predicting flow separation and the behavior of the air right next to the wall. The simulation was set up with air flowing over the Leading Edge Tubercle airfoil at a positive angle of attack, a scenario where standard blades would typically lose lift and stall.

Post-Processing: How Tubercles Energize the Flow

The results of the Leading Edge Tubercle ANSYS fluent simulation provide a fascinating look into bio-inspired aerodynamics. The key to the tubercle’s success lies in its ability to control the boundary layer, which is the thin layer of air sticking to the blade surface. In a normal blade, this layer gets tired and peels off (separates) when the angle is too steep, causing stall. However, the simulation shows that the tubercles act as “vortex generators.” The wavy shape creates pairs of counter-rotating vortices—swirling tunnels of air—that sit in the valleys between the bumps.

These vortices are engines of energy. They reach up into the fast-moving free stream of air above the blade and pull that high-energy air down onto the blade’s surface. This process is called “energizing the boundary layer.” By mixing this fresh, high-speed air with the slow air near the surface, the flow becomes stronger and more resistant to separation. The pressure contours confirm this mechanism clearly. We can see distinct regions of low pressure in the valleys, dropping to -125.6 Pa. This low pressure is the footprint of the strong vortices working to keep the flow attached. Because the flow stays attached longer, the blade generates more lift and less drag. Looking at the wake region behind the blade, the velocity colors show a range of 2-4 m/s. This relatively organized wake indicates that the chaotic, energy-sapping separation associated with deep stall has been avoided. This Leading Edge Tubercle CFD analysis proves that adding these simple bumps fundamentally changes the physics of the flow, allowing wind turbines to operate safely and efficiently in wider wind conditions.

Figure 2: Velocity and pressure contours showing the vortex generation and low-pressure zones.

Key Takeaways & FAQ

• Q: What is a Leading Edge Tubercle?
  • A: A tubercle is a bump or protrusion on the leading edge (front) of a wing or blade. In this Leading Edge Tubercle simulation, it mimics the bumps on a humpback whale’s flipper to improve aerodynamic performance.
• Q: How do tubercles prevent stall?
  • A: They prevent stall by generating streamwise vortices. As shown in the CFD results, these vortices mix high-energy air into the boundary layer, keeping the airflow attached to the blade surface even at high angles of attack.