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 .