  Eclipsing time variations (ETVs) in post-common-envelope binaries (PCEBs)
were proposed to be due to the time-varying component of the stellar
gravitational quadrupole moment. This is suggested to be produced by changes in
the stellar structure due to an internal redistribution of angular momentum and
the effect of the centrifugal force. We examined this hypothesis and present 3D
simulations of compressible magnetohydrodynamics (MHD) performed with the {\sc
Pencil Code}. We modeled the stellar dynamo for a solar-mass star with angular
velocities of 20 and 30 times solar. We included and varied the strength of the
centrifugal force and compared the results with reference simulations without
the centrifugal force and with a simulation in which its effect is enhanced.
The centrifugal force causes perturbations in the evolution of the numerical
model, so that the outcome in the details becomes different as a result of
nonlinear evolution. While the average density profile is unaffected by the
centrifugal force, a relative change in the density difference between high
latitudes and the equator of $\sim10^{-4}$ is found. The power spectrum of the
convective velocity is found to be more sensitive to the angular velocity than
to the strength of the centrifugal force. The quadrupole moment of the stars
includes a fluctuating and a time-independent component, which vary with the
rotation rate. As very similar behavior is produced in absence of the
centrifugal force, we conclude that it is not the main ingredient for producing
the time-averaged and fluctuating quadrupole moment of the star. In a real
physical system, we thus expect contributions from both components, that is,
from the time-dependent gravitational force from the variation in the
quadrupole term and from the spin-orbit coupling that is due to the persistent
part of the quadrupole.
