  In recent years, high-order discontinuous Galerkin (DG) methods have emerged
as an attractive approach for numerical simulations of compressible flows. This
paper presents an overview of the recent development of DG methods for
compressible flows with particular focus on hypersononic flows. First, we
survey state-of-the-art DG methods for computational fluid dynamics. Next, we
discuss both matrix-based and matrix-free iterative methods for the solution of
discrete systems stemming from the spatial DG discretizations of the
compressible Navier-Stokes equations. We then describe various shock capturing
methods to deal with strong shock waves in hypersonic flows. We discuss
adaptivity techniques to refine high-order meshes, and synthetic boundary
conditions to simulate free-stream disturbances in hypersonic boundary layers.
We present a few examples to demonstrate the ability of high-order DG methods
to provide accurate solutions of hypersonic laminar flows. Furthermore, we
present direct numerical simulations of hypersonic transitional flow past a
flared cone at Reynolds number $10.8 \times 10^6$, and hypersonic transitional
shock wave boundary layer interaction flow over a flat plate at Reynolds number
$3.97 \times 10^6$. These simulations run entirely on hundreds of graphics
processing units (GPUs) and demonstrate the ability of DG methods to directly
resolve hypersonic transitional flows, even at high Reynolds numbers, without
relying on transition or turbulence models. We end the paper by offering our
perspectives on error estimation, turbulence modeling, and real gas effects in
hypersonic flows.
