With wind power emerging as a key energy source around the world, Princeton researchers are exploring a new idea to squeeze more energy out of the whirling devices: flip them.

Love them or hate them, the silhouettes of turbine farms are becoming a fixture of the modern landscape — the stalk of a metal tower topped by a giant propeller turning slowly in the wind. These standard turbines, in which the shaft runs horizontal to the ground, have benefited from decades of research into aircraft propellers, resulting in high efficiency.

But research teams led by associate professors Elie Bou-Zeid and Luigi Martinelli Ph.D. ’87, and Alexander Smits, the Eugene Higgins Professor of Mechanical and Aerospace Engineering, are asking whether engineers can create more efficient turbine arrays using vertical turbines. Turning the shaft vertically — like mixer beaters rather than airplane propellers — has some advantages. For one, builders can place the turbine’s generator at the base of the tower instead of mounting it on the top. The vertical turbines are also easier to use underwater and offshore. And unlike horizontal turbines, vertical turbines do not have to change direction to follow the wind direction.

Lastly, following a proposal originally developed by John Dabiri BSE ’01, now a professor at Stanford University, the researchers are seeking more efficient ways to group multiple turbines.

“You can fit more of them in an area,” said Martinelli, an associate professor of mechanical and aerospace engineering. “Also, it might be possible to arrange a set of vertical turbines to increase their overall efficiency.”