This might look like the cut-stick project of a small child, but in fact this image visualises the noise that a helicopter makes as it tears through the air. Really.
Yes, that sounds a little crazy, but it’s made possible by the fact that as those rotors punch through the atmosphere, they set up a vortex at their tips. As the blades spin and hit the vortices of their neighbours, they make the loud chopping noise that’s so familiar. All that complex fluid flow results in areas of wildly different pressure around the chopper, which ends up rippling through the air to our ears.
A team of researchers from the German Aerospace Center realised that the varying air densities — a result of the varying pressures — would make light passing through the region bend in subtlety different ways — just like the heat haze on a road is caused by subtle differences in temperature. And that’s what you see in this image: A picture of the varying air density around the craft, which propagates to you through the air as that intense chopping sound. [DLR via New Scientist]
Picture: DLR