Flame precession of fire whirls: A further experimental study

•Experimental analyses on flame precession of quasi-steady fire whirls are presented.•The correlation of flame precession frequency agrees well with experimental data.•The flame precession of fire whirl is essentially dominated by aerodynamics.•Variations of precession radius and precession velocity are clarified.

Following our previous work (Proc. Combust. Inst. 2013, 34: 2607–2615), this work presents a further experimental investigation on the flame precession of quasi-steady fire whirls. Six small to medium-scale fixed-frame facilities and a small-scale rotating screen facility were used for experiments. The fixed-frame facilities were square and hexagon in cross sections, with four and six symmetric corner gaps respectively. It was found that the flame precession frequency was identical to the screen rotating frequency in the rotating screen facility, and close to the characteristic flow revolution frequency in the fixed-frame facilities. The proposed correlation of precession frequency agreed reasonably with the experimental data. It was proved that the flame precession is essentially dominated by aerodynamics. The precession radius increased first and then remained relatively steady when a critical screen rotating frequency was reached, and the critical frequency increased with the heat release rate. For the fixed-frame facilities, the boundary conditions at the base had significant influence on flame precession radius and frequency.