  This work presents a review of high-order hybridisable discontinuous Galerkin
(HDG) methods in the context of compressible flows. Moreover, an original
unified framework for the derivation of Riemann solvers in hybridised
formulations is proposed. This framework includes, for the first time in an HDG
context, the HLL and HLLEM Riemann solvers as well as the traditional
Lax-Friedrichs and Roe solvers. HLL-type Riemann solvers demonstrate their
superiority with respect to Roe in supersonic cases due to their positivity
preserving properties. In addition, HLLEM specifically outstands in the
approximation of boundary layers because of its shear preservation, which
confers it an increased accuracy with respect to HLL and Lax-Friedrichs. A
comprehensive set of relevant numerical benchmarks of viscous and inviscid
compressible flows is presented. The test cases are used to evaluate the
competitiveness of the resulting high-order HDG scheme with the aforementioned
Riemann solvers and equipped with a shock treatment technique based on
artificial viscosity.
