  Rayleigh-Taylor (RT) unstable flames are a key component of Type Ia and Iax
supernovae explosions, but their complex hydrodynamics is still not well
understood. These flames are affected not only by the RT instability, but also
by the turbulence it generates. Both processes can increase the flame speed by
stretching and wrinkling the flame. This makes it hard to choose a subgrid
model for the flame speed in full star Type Ia or Iax simulations. Commonly
used subgrid models get around this difficulty by assuming that either the RT
instability or turbulence is dominant and sets the flame speed. In previous
work, we evaluated the physical assumptions and predictive abilities of these
two types of models by analysing a large parameter study of 3D direct numerical
simulations of RT unstable flames. Surprisingly, we found that the flame
dynamics is dominated by the RT instability and that RT unstable flames are
very different from turbulent flames. In particular, RT unstable flames are
thinner rather than thicker when turbulence is strong. In addition, none of the
turbulent flame speed models adequately predicted the flame speed. We also
showed that the RT flame speed model failed when the RT instability was strong,
suggesting that geometrical burning effects also influence the flame speed.
However, these results depended on simulations with $Re\lesssim720$. In this
paper, we extend the parameter study to higher Reynolds number and show that
the basic conclusions of our previous study still hold when the RT-generated
turbulence is stronger.
