We address the differences observed due to heat release between reacting and non-reacting versions of otherwise identical shear flows under conditions for which buoyancy
effects are negligible. The differences considered here result from density changes
produced by exothermic reaction, and are shown to be similar to those produced by
free-stream density differences in non-reacting flows. The piecewise linear variations
of temperature with mole fraction allow the density changes due to exothermic reaction
to be related to an equivalent non-reacting flow, in which the temperature of
one of the fluids is raised to an effective value determined by the peak temperature
and overall stoichiometry. This leads to a general equivalence principle by which the
scaling laws for non-reacting flows can be extended to predict effects of heat release
by exothermic reaction. This equivalence principle is then applied to axisymmetric
turbulent jets, where it leads to a generalized momentum diameter d+ in which the
scaling laws for burning and non-burning jets become identical – it effectively extends
the classical momentum diameter d* of Thring & Newby (1953) and Ricou &
Spalding (1961) to exothermic reacting flows. The resulting predicted effects of heat
release, in both the near and far fields, show good agreement with experimental data
from momentum-dominated turbulent jet diffusion flames. The equivalence principle
is then applied to planar turbulent jets, for which it also accurately predicts the
observed effects of combustion heat release.