Effect of Nozzle Height on the Combustion Dynamics of Jet Fires in Rotating Flow Fields

In this paper, the effect of nozzle height on the combustion dynamics of jet fires in rotating flow fields (JFRFFs) is systematically investigated through experimental and numerical simulations. As the nozzle height increases, the JFRFF flame state transitions from stable rotation (SR) to unstable rotation (USR), and eventually to non-rotation (NR), indicating a weakening interaction between the vortex flow and the jet flame. The radial distribution of tangential velocity gradually deviates from the Burgers vortex model as the nozzle height increases, providing a criterion for distinguishing different flame states. Both vortex intensity and flame length are found to decrease with increasing nozzle height, whereas the maximum flame diameter increases. The relative position of the maximum flame diameter to the whole flame length firstly increases and then decreases to match that of the free jet fires, as the flame evolves from SR to USR and NR. In addition, the air entrainment near the nozzle exit decreases with increasing nozzle height, as evidenced by the gradual rise in lift-off height. These findings establish a theoretical basis for the fire performance design of flares in pipeline retrofitting and process industries.