Oscillation frequency of buoyant diffusion flame in cross-wind

Abstract

Phenomenological studies relating to the oscillation of buoyant diffusion flames are very important to design flare systems in the energy and petrochemical industry or develop an image recognition algorithm for wind-aided fire detection. In this work, the oscillation frequency for the “down-wash mode” buoyant diffusion propane flames (momentum flux ratio of jet to cross-wind<0.1, 6×10−5<Froude number of the fuel flow<2×10−2, 102<Richardson number<104) were investigated. The experiments were conducted in a wind tunnel, and a kinematic model of the global oscillation frequency was established. The results show that: With the increasing cross-wind velocity, the flames bases are augmented by the “friction force” to cover more area of the near wake of the nozzle, with more length and area of the continuous regions of the flame. Coupling the influences of buoyancy acceleration, entrainment deceleration and “friction force” on the axial fuel velocity, the formula of the puffing frequency was deduced through introducing a buoyancy and friction force related coefficient and a decay coefficient that employs the entrainment deceleration of the axial velocity. This model was validated by the experimental results with good agreements. The flame frequency increases with increasing velocity ratio of cross-wind to jet flow. The decay coefficient is less than unity, ensuring longer flow times, enabling the theoretical model to have a good predictive capability.