Hermann Ludwig Ferdinand von Helmholtz was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Association, the largest German association of research institutions, is named in his honour.
Hermann von Helmholtz
Helmholtz's polyphonic siren, Hunterian Museum, Glasgow
Helmholtz in 1848
1889 copy of Helmholtz's "Uber die Erhaltung der Kraft", no. 1
In fluid dynamics, hydrodynamic stability is the field which analyses the stability and the onset of instability of fluid flows. The study of hydrodynamic stability aims to find out if a given flow is stable or unstable, and if so, how these instabilities will cause the development of turbulence. The foundations of hydrodynamic stability, both theoretical and experimental, were laid most notably by Helmholtz, Kelvin, Rayleigh and Reynolds during the nineteenth century. These foundations have given many useful tools to study hydrodynamic stability. These include Reynolds number, the Euler equations, and the Navier–Stokes equations. When studying flow stability it is useful to understand more simplistic systems, e.g. incompressible and inviscid fluids which can then be developed further onto more complex flows. Since the 1980s, more computational methods are being used to model and analyse the more complex flows.
This is an image, captured in San Francisco, which shows the "ocean wave" like pattern associated with the Kelvin–Helmholtz instability forming in clouds.