We develop a suite of 3D hydrodynamic models of supernova remnants (SNRs)
expanding against the circumstellar medium (CSM). We study the Rayleigh-Taylor
Instability (RTI) forming at the expansion interface by calculating an angular
power spectrum for each of these models. The power spectra of young SNRs is
seen to exhibit a dominant angular mode, which is a diagnostic of their ejecta
density profile as found by previous studies. The steep scaling of power at
smaller modes and the time evolution of the spectra is indicative of absence of
a turbulent cascade. Instead, as the time evolution of the spectra suggests,
they may be governed by an angular mode dependent net growth rate. We also
study the impact of anisotropies in the ejecta as well as in the CSM on the
power spectra of velocity and density. We confirm that perturbations in the
density field (whether imposed on the ejecta or the CSM) do not influence the
anisotropy of the remnant significantly unless they have a very large amplitude
and form large-scale coherent structures. In any case, these clumps can only
affect structures on large angular scales. The power spectra on small angular
scales is completely independent of the initial clumpiness and only governed by
the growth and saturation of the Rayleigh-Taylor instability.Comment: 10 pages, 8 figures; submitted to ApJ. Comments are welcom