  Consider a windtree model with several parallel arbitrary right-angled
obstacles placed periodically on the plane. We show that its diffusion rate is
the largest Lyapunov exponent of some stratum of quadratic differentials and
exhibit a new general strategy to compute the generic diffusion rate of such
models. This result enables us to compute numerically the diffusion rates of a
large family of models, and to observe its asymptotic behaviour according to
the shape of the obstacles.
