He worked in the Aeronautical Research Laboratories, Melbourne (1962–63, and 1965–1967), and in the Physics Department of the Australian National University (1967–1980), with a sabbatical year as a Humboldt Fellow in Darmstadt, Germany, 1974.

In 1980 he accepted an offer to head the Institute for Experimental Fluid Mechanics of the DLR in Göttingen, Germany.

He has made contributions in gas dynamics, notably Mach reflection and effects of dissociation, in separated flows, and in wind tunnel technology.

In 1997, Hornung was elected a member of the National Academy of Engineering for contributions to hypersonics and aerodynamics.

[1] Hans G. Hornung, Dimensional Analysis: Examples of the Use of Symmetry, Dover Publications (2006)