  Non-stationary Euler flows of gases are studied. The system of differential
equations describing such flows can be represented by means of 2-forms on
zero-jet space and we get some exact solutions by means of such a
representation. Solutions obtained are multivalued and we provide a method of
finding caustics, as well as wave front displacement. The method can be applied
to any model of thermodynamic state as well as to any thermodynamic process. We
illustrate the method on adiabatic ideal gas flows.
