Numerical Simulation of the Blue Whirl

Major Goals The overriding goal, the real objective of the current proposal, is to develop a three-dimensional unsteady numerical model that can be used to simulate the unsteady behavior of fire whirls. The model must be capable of simulating the dynamics of the transition between fire whirls and the blue whirl. There were three major goals in the project that contribute to the overall objective 1. Test the basic fluid algorithm for solving the unsteady, compressible Navier-Stokes equations by predicting vortex breakdown in the same general regime of temperature and pressure as the blue whirl. 2. Develop a calibrated, simplified chemical-diffusive model CDM for heptane-air vapor combustion. The model should cover a range of equivalence ratios from fuel-lean to fuel-rich conditions. 3. Produce a first-pass simulation for conditions that might evolve into a blue whirl. Coordinate this with ongoing experiments at ARL Adelphi and the University of Maryland.Accomplishments The accomplishments of the program were generally aligned with the goals. We therefore 1. Tested the basic fluid algorithm for solving the unsteady, compressible Navier-Stokes Equations in the same regime of temperature and pressure as we expect to see a fire whirl than transitions to a blue whirl. For this, we tested the standard explicit computation, and then began the conversion to a low-mach-number version which would be affordable. The test problem was computation of vortex breakdown. We now tested models that areaffordable for high-speed and low-speed flow. 2. Developed and begun the calibrated, of a simplified chemical-diffusive CDM model for heptane-air vapor combustion. The model should cover a range of dilutions from fuel-lean to fuel-rich conditions. The diffusion flame model is being tested and calibrated now.