Effects of multiple-scale driving on turbulence statistics
  Turbulence is ubiquitous in astrophysical fluids such as the interstellar
medium (ISM) and the intracluster medium (ICM). In turbulence studies, it is
customary to assume that fluid is driven on a single scale. However, in
astrophysical fluids, there can be many different driving mechanisms that act
on different scales. If there are multiple energy-injection scales, the process
of energy cascade and turbulence dynamo will be different compared with the
case of single energy-injection scale. In this work, we perform
three-dimensional incompressible/compressible magnetohydrodynamic (MHD)
turbulence simulations. We drive turbulence in Fourier space in two wavenumber
ranges, 2\$\leq k \leq \sqrt{12}\$ (large-scale) and 15 \$\lesssim k \lesssim
\$ 26 (small-scale). We inject different amount of energy in each range by
changing the amplitude of forcing in the range. We present the time evolution
of the kinetic and magnetic energy densities and discuss the turbulence dynamo
in the presence of energy injections at two scales. We show how kinetic,
magnetic and density spectra are affected by the two-scale energy injections
and we discuss the observational implications. In the case \$\epsilon_L <
\epsilon_S\$, where \$\epsilon_L\$ and \$\epsilon_S\$ are energy-injection
rates at the large and small scales, respectively, our results show that even a
tiny amount of large-scale energy injection can significantly change the
properties of turbulence. On the other hand, when \$\epsilon_L \gtrsim
\epsilon_S\$, the small-scale driving does not influence the turbulence
statistics much unless \$\epsilon_L \sim \epsilon_S\$.
