  An axisymmetric model for the Crab Nebula is constructed to examine the flow
dynamics in the nebula. The model is based on that of Kennel and Coroniti
(1984), although we assume that the kinetic-energy-dominant wind is confined in
an equatorial region. The evolution of the distribution function of the
electron-positron plasma flowing out in the nebula is calculated. Given viewing
angles, we reproduce an image of the nebula and compare it with Chandra
observation.
  The reproduced image is not a ring-like but rather 'lip-shaped'. It is found
that the assumption of toroidal field does not reproduce the Chandra image. We
must assume that there is disordered magnetic field with an amplitude as large
as the mean toroidal field. In addition, the brightness contrast between the
front and back sides of the ring cannot be reproduced if we assume that the
magnetization parameter $\sigma$ is as small as $\sim 10^{-3}$. The brightness
profile along the semi-major axis of the torus is also examined. The
non-dissipative, ideal-MHD approximation in the nebula appears to break down.
We speculate that if the magnetic energy is released by some process that
produce turbulent field in the nebula flow and causes heating and acceleration,
e.g. by magnetic reconnection, then the present difficulties may be resolved
(i.e. we can reproduce a ring image, and a higher brightness contrast). Thus,
the magnetization parameter $\sigma$ can be larger than previously expected.
