One of the greatest challenges in today’s society is to reduce the consumption of fuel used in transport and to develop more effective ways of harnessing wind energy. Consequently, both the aviation and wind power industries are looking for new, more efficient designs.
“By understanding what makes birds so fantastic in flight, we gain not only new knowledge, but also inspiration for new technical solutions”, says evolutionary biologist Christoffer Johansson of the Department of Biology at Lund University.
The design is crucial
Christoffer Johansson studies birds’ adaptations for flight by observing the interplay between wing structure, wing movement and how air flows over the wings (aerodynamics). When birds fly, they flap their wings and these movements create a flow of air similar to that created by rotating propellers. The aim, when a flying bird is subjected to turbulence or gusts of wind, is to achieve a high aerodynamic performance to save energy. The wings, therefore, need to have an efficient design and the airflow over them must be kept stable.
It is the contours of feathers, and their passive movement when subjected to air flow, that is crucial for the aerodynamics, explains Christoffer Johansson.
A feather consists of dead material, just like our nails, with a very complex structure. It is pliant and easily deformed by the airflow, which in turn also affects how the air flows over the wings.
“It’s therefore relevant to study bird feathers in order to obtain better propeller and turbine blade designs”, points out Christoffer Johansson.
Computer simulations are needed
Christoffer Johansson and his colleagues are now working to identify what makes bird feathers so well adapted for flying. The project will include tests in which the researchers manipulate the airflow and the feathers’ mechanical and aerodynamic characteristics.
“However, as we can’t manipulate real feathers, we need to use computer simulations”, states Christoffer Johansson.
This requires models that allow for a material not being completely stable – feathers change shape when they are affected by the flow. These are known as Fluid-Structure Interaction (FSI) models.
A 3D data model of a feather
The researchers on the project will soon have developed a 3D data model of a feather (see fig), which will then be used in the simulations. However, a considerable amount of modelling work remains to be done by Christoffer’s colleagues when they are to adapt their current FSI model so it can be used in the feather experiments. The feather’s structure is much more complex than any other previously modelled by the researchers, and even with access to the Aurora supercomputer at Lunarc, the centre for scientific and technical computing at Lund University, there will probably not be sufficient computing capacity to model the full complexity.
“We must simplify the model, while retaining the complexity – my research colleagues will need to be creative”, says Christoffer Johansson.
Test in wind tunnel
In parallel, to test the relevance of the simulation results, Christoffer Johansson will try out the models in reality, namely in a wind tunnel.
“We will print out an enlarged 3D model of the feather and mount it in our wind tunnel. We turn on the wind and measure the flow over the feathers. In this way, we can later confirm that the models are OK.”
Finally, when the model works, the researchers will move on to the simulation experiments in order to gradually increase understanding of the feather’s passive aerodynamic control mechanisms.
“When we can identify the mechanism behind birds’ passive flow control, we can transfer that regulation relatively easily to technical solutions. It is going to be exciting to be involved later in the project when we can cooperate with industry in the design of wings for the aviation industry and turbine blades for wind turbines”, concludes Christoffer Johansson.
