Laminar to turbulent nonpremixed flame with swirl

Laboratory nonpremixed/diffusion flame. Laminar to turbulent transition. Coflow swirled air added resulting in liftoff, attachment, and ultimately blowout. See also • Turbulent diffusion fl...
Fuel flow rate is increased resulting in a longer laminar flame. This transitions to a weakly turbulent flame. Coflow swirled air is then added with increasing flow rate. The flame volume, height, and luminosity all decrease. At the highest air flow blowout occurs.
See ignite.byu.edu/che633

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why the flame become turbulent?