  In this paper we numerically study the behavior of the density power spectrum
in turbulent thermally bistable flows. We analyze a set of five
three-dimensional simulations where turbulence is randomly driven in Fourier
space at a fixed wave-number and with different Mach numbers M (with respect to
the warm medium) ranging from 0.2 to 4.5. The density power spectrum becomes
shallower as M increases and the same is true for the column density power
spectrum. This trend is interpreted as a consequence of the simultaneous
turbulent compressions, thermal instability
  generated density fluctuations, and the weakening of thermal pressure force
in diffuse gas. This behavior is consistent with the fact that observationally
determined spectra exhibit different slopes in different regions. The values of
the spectral indexes resulting from our simulations are consistent with
observational values. We do also explore the behavior of the velocity power
spectrum, which becomes steeper as M increases. The spectral index goes from a
value much shallower than the Kolmogorov one for M=0.2 to a value steeper than
the Kolmogorov one for M=4.5.
