The goal of cosmological fluid dynamics simulations is to understand the formation and evolution of the baryonic structures in the universe which we observe with telescopes (e.g., galaxies, clusters). The evolution of cosmic baryons is described by Euler or MHD equations in an expanding universe, subject to the gravitational influence of cold dark matter--the dominant mass component in the universe. The gravitational clustering of cold dark matter, which drives the baryonic evolution, occurs across a vast range of length and timescales, and has been extensively simulated using high resolution N-body methods. The multiscale dynamics of structure formation, together with the multiphysics nature of cosmic plasmas, make cosmological fluid dynamics a grand challenge problem. Two principal methods have been developed to meet these challenges: Lagrangian smoothed particle hydrodynamics (SPH), and Eulerian adaptive mesh refinement (AMR). The former is in widespread use in the numerical cosmology community. In this talk I will report on the latter. I will describe Enzo, a parallel, hybrid, cosmological fluid dynamics code first developed by Greg Bryan, and later extended to include more physics. I will overview the physics and algorithms currently in Enzo, and compare its results with a state-of-the-art SPH code. I will present applications of Enzo to the formation of clusters of galaxies, early galaxies and cosmic reionization. I will conclude with future plans. Enzo is available at http://cosmos.ucsd.edu/enzo.
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