  Magnetorotational turbulence draws its energy from gravity and ultimately
releases it via dissipation. However, the quantitative details of this energy
flow have not been assessed for global disk models. In this work we examine the
energetics of a well-resolved, three-dimensional, global magnetohydrodynamic
accretion disk simulation by evaluating statistically-averaged mean-field
equations for magnetic, kinetic, and internal energy using simulation data. The
results reveal that turbulent magnetic (kinetic) energy is primarily injected
by the correlation between Maxwell (Reynolds) stresses and shear in the (almost
Keplerian) mean flow, and removed by dissipation. This finding differs from
previous work using local (shearing-box) models, which indicated that turbulent
kinetic energy was primarily sourced from the magnetic energy reservoir.
Lorentz forces provide the bridge between the magnetic and kinetic energy
reservoirs, converting ~ 1/5 of the total turbulent magnetic power input into
turbulent kinetic energy. The turbulent energies (both magnetic and kinetic)
are mainly driven by terms associated with the turbulent fields, with only a
minor influence from mean magnetic fields. The interaction between mean and
turbulent fields is most evident in the induction equation, with the mean
radial magnetic field being strongly influenced by the turbulent electromotive
force (EMF). During the quasi-steady turbulent state roughly 2/3 of the
Poynting flux travels into the corona, with the remainder transporting magnetic
energy in the radial direction. In contrast to previous studies, the
stress-related part of the Poynting flux is found to dominate, which may have
important implications for "reflection" models of Seyfert galaxy coronae that
typically invoke a picture of buoyant rising of magnetic flux tubes via
advection.
