  We present a novel reaction analogy (RA) based forcing method for generating
stationary scalar fields in incompressible turbulence. The new method can
produce more general scalar PDFs (e.g. double-delta) than current methods,
while ensuring that scalar fields remain bounded. Such features are useful for
generating initial fields in non-premixed combustion or for studying
non-Gaussian scalar turbulence. The RA method mathematically models
hypothetical chemical reactions that convert reactants in a mixed state back
into its pure unmixed components. Various types of chemical reactions are
formulated and the corresponding mathematical expressions derived such that the
reaction term is smooth in the scalar space and is consistent with mass
conservation. For large values of the scalar dissipation rate, the method
produces statistically steady double-delta scalar PDFs. Quasi-uniform,
Gaussian, and stretched exponential scalar statistics are recovered for smaller
values of the scalar dissipation rate. The shape of the scalar PDF can be
further controlled by changing the stoichiometric coefficients of the reaction.
The ability of the new method to produce fully developed passive scalar fields
with quasi-Gaussian PDFs is also investigated, by exploring the convergence of
the third order mixed structure function to the "four-thirds" Yaglom's law.
