You know that: Above you, a jet plane flies past and then it pops. The plane broke the sound barrier. But why is there a bang? Due to the high speed, the air condenses around the aircraft, the resistance increases - until it is finally overcome. Then the jet flies at supersonic speed. And then it pops. The audible strike physicists call compression shock. This is a term from fluid mechanics. And whenever the flow state of gases or liquids abruptly changes, a compression shock occurs.
If the flow state of a drop of water suddenly changes, then what you see in the picture above happens. Using a computer simulation, Nikolaus A. Adams from the Technical University of Munich and his co-workers Luhui Han and Xiangyu Hu projected the event. "At the center is the 'torn' phase boundary between gas and water, represented by the bluish density gradient false colors, " says Nikolaus A. Adams describing the model. "The yellow-reddish colors are density gradients of the collision that has already passed from top to bottom over the water droplet with numerous reflections at the phase boundary and walls."
With their research, Adams and his colleagues want to find out whether compression shocks can also be used for therapies. For example, in the human body to control cancerous tumors with controlled bumps.
Photo: N. Adams / TU Munich Display© science.de - Ruth Roebuck / Karin Schlott