基于旋流火焰根部熄火现象的FGM模型研究

A series of experimental measurements on a prototype premixed swirl burner with complex geometry were carried out using CH₂O/OH-PLIF. FGM method(SFGM)taking account of strain rate was developed to study two modes of premixed swirl flame, one stabilized and the other close to blown-off flame under the same Reynolds number(Re=10000). The SFGM model in this work is related to a reaction factor, which controls the source reaction rate directly without extra dimension extension of strain rate, and thus this method could save considerable calculation time. By comparing the experimental and numerical results(OH and CH₂O×OH distributions), it is clearly found that SFGM coupled with LES can capture much better results than the FGM model without considering strain rate. Specifically, the SFGM model can predict the flame structure correctly, e.g. no attached flame survives near the premixed tube exit compared with the FGM model in which the flame still survives, and the close to blow-off flame has a greater lift-off height than the stabilized flame. In addition, turbulent flame speed is proportional to turbulent fluctuation speed. The edge of main flame front is revealed to be determined jointly by the flow velocity expanding downstream and the main turbulent flame(in the CRZ)propagation velocity propagating upstream. When the equivalence ratio is decreased to the flammability limit, the reactants in the CRZ are diluted by the leaner mixtures, leading to the breaking of contact flame into smaller flame kernels. Moreover, the turbulent flame speed declines with the decreasing flame temperature while the flow speed is kept fixed, resulting in the flame front propagating downstream away from CRZ and finally blowing off.