  Numerical test of isotropic turbulence compressibility reduction with
helicity in a cyclic box is performed. The ratios of
compressibility-relevant-mode spectra over those of kinetic energy present
power laws at large wavenumbers in the dissipation range, indicating a common
difference of $11/15$ in the exponents of the algebraic prefactor of the
nonhelical power spectra over those of helical ones. Our results being not
derived from the shapes of the spectra themselves, the implied information
about the helicity effect on the complex singularities of the discretized
dynamical system can still be of reasonable value for insights of the
Navier-Stokes equation, although the high-order finite difference scheme used
for computation may not be as accurate in dissipation range as the
state-of-the-art of incompressible turbulence with pseudo-spectral method.
Possible applications in controlling flows, for the purposes of, say,
decreasing turbulence noise, are also discussed according to the spectral
fluctuations.
