  The morphology of young Pulsar Wind Nebulae (PWN) is largely determined by
the properties of the wind injected by the pulsar. We have used a recent
parametrization of the wind obtained from Force Free Electrodynamics
simulations of pulsar magnetospheres to simulate nebulae for different sets of
pulsar parameters. We performed axisymmetric Relativistic Magnetohydrodynamics
simulations to test the morphology dependence of the nebula on the obliquity of
the pulsar and on the magnetization of the pulsar wind. We compare these
simulations to the morphology of the Vela and Crab PWN. We find that the
morphology of Vela can be reproduced qualitatively if the pulsar obliquity
angle is alpha ~45deg and the magnetization of the wind is high (sigma_0 ~
3.0). A morphology similar to the one of the Crab Nebula is only obtained for
low magnetization simulations with alpha >~ 45deg. Interestingly, we find that
Kelvin-Helmholtz instabilities produce small scale turbulences downstream of
the reverse shock of the pulsar wind.
