  In this work we present an a posteriori error indicator for approximation
schemes of Runge-Kutta-discontinuous-Galerkin type arising in applications of
compressible fluid flows. The purpose of this indicator is not only for mesh
adaptivity, we also make use of this to drive model adaptivity. This is where a
perhaps costly complex model and a cheaper simple model are solved over
different parts of the domain. The a posteriori bound we derive indicates the
regions where the complex model can be relatively well approximated with the
cheaper one. One such example which we choose to highlight is that of the
Navier-Stokes-Fourier equations approximated by Euler's equations.
