  [Abridged] The torque exerted by an external potential on a two-dimensional
gaseous disk at non-co-orbital corotation resonances is studied by means of
numerical simulations. The degree of saturation of these resonances is
important in determining whether an eccentric giant planet embedded in a
protoplanetary disk experiences an eccentricity excitation or damping. We
perform calculations restricted to one or two resonances to investigate the
properties of two neighboring corotation resonances, as well as the properties
of a corotation resonance that overlaps a Lindblad resonance. We find that
these properties hardly differ from the case of an isolated corotation
resonance. In particular, although the torque of two neighboring corotation
resonances may differ from the sum of the torques of the corresponding
resonances considered as isolated, it never exceeds the sum of the fully
unsaturated isolated corotation resonances, and it saturates in a fashion
similar to an isolated resonance. Similarly, the presence of an underlying
Lindblad resonance hardly affects the corotation torque, even if that resonance
implies a torque strong enough to significantly redistribute the azimuthally
averaged surface density profile, in which case the corotation torque scales
with the resulting vortensity gradient. This set of numerical experiments thus
essentially validates previous analytic studies. As a side result, we show that
corotation libration islands misrepresented by a mesh of too low resolution can
lead to a strongly overestimated corotation torque. This may be an explanation
why the eccentricity of embedded Jupiter-sized planets was never observed to
undergo an excitation in the numerical simulations performed so far.
