The humpback whale has an astonishing feature: the leading edge of its long fins is not smooth. It has a series of bumps called tubercles. Researchers adapted this shape to modify the blades of an aircraft propulsion simulator. Their idea is to guide the air more effectively around the blades as they rotate.
To understand the value of these bumps, we need to look at what happens to the air on a blade. Under certain conditions, the flow can separate from the surface and form vortices. Some of the energy is then lost. The whale-inspired geometry changes the air circulation and limits this phenomenon in the model studied.
Humpback whale showing its long pectoral fin in the ocean.
Credit: Wikimedia Commons.
Wikimedia image
The researchers built a numerical model capable of calculating both the air movement and the deformation of the blades. Several shapes could therefore be compared.
The differences obtained in this simulation are significant. With the bumps, the airflow passing through a channel between the blades increases by 4.09%. The ratio between outlet and inlet pressure rises by 4.85%. The authors also calculate a marked increase in blade efficiency, from 67.014% to 89.861% in the optimized configuration.
The modification does not appear to make the blade more fragile in the model. Its maximum deformation, relative to the disk diameter, decreases from 0.306% to 0.239%. In other words, the modified blade deforms slightly less under the calculated loads. However, this result remains theoretical at this stage.
Why can a whale fin serve as a model for an aircraft component? In both cases, a surface must move efficiently through a fluid: water for the animal, air for the blade. The bumps locally change how this fluid flows around the surface. Their shape can therefore delay certain unfavorable flow patterns.
The next step will be to move beyond simulation. The authors indicate that the structure still needs to be optimized to improve its rigidity and reliability in service. Physical tests will be necessary before determining whether the calculated gains can be reproduced on a real blade subjected to the stresses of a propulsion system.