Compressible and Reactive Navier-Stokes Simulations of a Forced Fire Whirl *

A fire whirl forms when there is strong coupling of circulation and combustion of reactive material. In this work, we demonstrate the capability of a recently developed numerical model to simulate fire whirls. We consider a square enclosure that is open at the top and closed at the bottom with air forced in at the corners. The bottom wall has a constant flux of heptane in a specified diameter at the center. The convective portion of the compressible and reactive Navier-Stokes equations are solved using the barely implicit correction (BIC) and fourth-order flux corrected transport (FCT) algorithms. All diffusion terms use three-point central for spatial discretization and 2^nd order Runge-Kutta time integration. The chemical energy release is modeled using the chemical-diffusive model. The results show Rankine-like vortex near the flame sheet. Buoyancy produces a jet-like vertical velocity profile. Furthermore, by reducing the circulation and fuel flow rate, we observe a state of reactive vortex breakdown. We examine and compare the structure of this state to the fire whirl.