This exhibit illustrates basic aerodynamics. The visitor experiments with different shapes of windmill blades. The efficiency of windmill blades depends on its shape and the speed of the wind.
Wind tunnels are used to test the wings of aeroplanes or windmills for their efficiency to generate lift or to produce energy. The shape of an aircraft wing influences the air to go faster over the top of the wing than the wind, which goes underneath the wing. The difference in speed results in the upper surface feeling a partial vacuum (low-pressure) and the undersurface feeling an overpressure.