  Flickering buoyant diffusion methane flames in weakly rotatory flows were
computationally and theoretically investigated. The prominent computational
finding is that the flicker frequency nonlinearly increases with the rotational
intensity number R (up to 0.24), which measures the relative importance of the
rotational speed compared with the methane jet speed. This finding is
consistent with the previous experimental observations that flame flicker is
enhanced by rotatory flows within a certain extent. Based on the
vortex-dynamical understanding of flickering flames that the flame flicker is
caused by the periodic shedding of buoyancy-induced toroidal vortices, we
formulated a scaling theory for flickering buoyant diffusion flames in weakly
rotatory flows. The theory predicts that, with respect to the flicker frequency
f_0 at R=0, the increase of the flicker frequency f at nonzero R obeys the
scaling relation f-f_0~R^2, which agrees very well with the present
computational results. In physics, the externally rotatory flow enhances the
radial pressure gradient around the flame, and the significant baroclinic
effect contributes an additional source for the growth of toroidal vortices so
that their periodic shedding is faster.
