Numerical viscosity in hydrodynamics simulations in general relativity

We present an alternative method to estimate the numerical viscosity in simulations of astrophysical objects, which is based on the damping of fluid oscillations. We apply the method to general relativistic hydrodynamic simulations using spherical coordinates. We perform 1D spherical and 2D axisymmetric simulations of radial oscillations in spherical systems. We first calibrate the method with simulations with physical bulk viscosity and study the differences between several numerical schemes. We apply the method to radial oscillations of neutron stars and we conclude that the main source of numerical viscosity in this case is the surface of the star. We expect that this method could be useful to compute the resolution requirements and limitations of the numerical simulations in different astrophysical scenarios in the future.