###### Abstract
Such building geometrical configuration could potentially act as to induce the eddy generation and hence pose a risk to trigger the formulation of fire whirl in a fire incident. For instance, despite the recently developed bio-based flame-retardant materials that effectively restrain the fire from spreading [18; 19; 20; 21; 22], the occurrence of the swirling flame has been observed in some recent high profile skyscraper fire incidents including the Beijing Television Cultural Center, Plasco Building, Grenfell Tower, etc. [23]. Understanding the formation of fire whirl and flaming behaviour in an enclosed configuration that resembles the high-rise buildings, is of great benefits to ensure the safety of the resident and occupant as well as to prevent property lost [24; 25; 26], and therefore is identified as the topic of this study. Figure 1: Example of the internal structure of a high-rise building features atrium and spiral staircase [17]. Fire whirl has been systematically investigated using experimental means during the past decades to characterise the flame structure and gain the understanding of the transformation of fire whirl from buoyancy-driven free-standing diffusion [7; 27; 28; 29; 30; 31; 32; 33]. However, there are some inevitable limitations associated with the experimental method. For instance, the parameters that could be quantified by an experimental approach are limited to temperature, velocity and exhaust gas concentration, which may not be sufficient to reveal the fundamental physical-chemical behaviour and probe the root causes of the observed flaming behaviour. In addition, if the intrusive measuring technique is implemented, e.g., thermocouple for temperature and bidirectional venturi tube for velocity, the experimental data obtained from the literature are often limited to a few points of interest, due to the constraint of the set locations of the measuring device and its associated spatial resolution. Nevertheless, as mentioned previously, the fire whirl is swirling in an unpredictable manner and the flaming structure may not reside in a fixed position. Furthermore, the existence of the measuring devices could inevitably be perturbative, hence potentially alter the very flow dynamics and combustion behaviour [34]. On the other hand, the optical-based diagnostic technique improves the data collection to planar scale without disturbing the measured conditions. It is, however, widely agreed that the optical properties that are critical for the reliability and accuracy of the optical-based measuring result, is often challenging to acquire [35]. The numerical approach hence can serve as a great aid to provide a completed set of data that is often difficult to assess by experimental means alone. The comprehensive data set generated by numerical simulation could work concurrently with experimental measurement to shed light on the fundamental understanding of this topic of interest. Through the literature review, it has been revealed that the sophisticated flaming behaviour of the fire whirl is governed by the entangled coupling between flow dynamics and combustion kinetics, which could be inevitably affected by various aspects, such as the temperature, buoyancy, vortex, the combustion reaction, etc. which are interrelated and interact during the formulation and evolution of the fire whirl. Such intriguing interaction makes the understanding of the not-well-understood fundamental of the swirling reaction flow more unfathomable. For example, the inception of fire whirl within the enclosure intensifies the combustion process and subsequently varies the energy transfer from the flame structure to the surroundings [36; 37; 38; 39]. If a pool fire configuration is used, the burning rate, which depends on the rate of the liquid fuel, convert into combustible gas mixture via evaporation will be inevitably altered, compared with non-swirled flame counterpart. As a result, ensuring combustion behaviour and heat release rate could also be affected.