  Upcoming large-scale-structure surveys can shed new light on the properties
of dark energy. In particular, if dark energy is a dynamical component, it must
have spatial perturbations. Their behaviour is regulated by the speed of sound
parameter, which is currently unconstrained. In this work we present the
numerical methods that will allow to perform cosmological simulations of
inhomogeneous dark energy scenarios where the speed of sound is small and
non-vanishing. We treat the dark energy component as an effective fluid and
build upon established numerical methods for hydrodynamics to construct a
numerical solution of the effective continuity and Euler equations. In
particular, we develop conservative finite volume schemes that rely on the
solution of the Riemann problem, which we provide here in both exact and
approximate forms for the case of a dark energy fluid.
