Publications

@article{Hariharan2019a,

title = {The blue whirl: Boundary layer effects, temperature and OH* measurements},

author = {Sriram Bharath Hariharan and Paul M Anderson and Huahua Xiao and Michael J Gollner and Elaine S Oran},

url = {https://doi.org/10.1016/j.combustflame.2019.02.018},

doi = {10.1016/j.combustflame.2019.02.018},

issn = {15562921},

year  = {2019},

date = {2019-01-01},

journal = {Combustion and Flame},

volume = {203},

pages = {352--361},

publisher = {Elsevier Inc.},

abstract = {The blue whirl is a small flame with an inverted conical shape, first observed as it developed from fire whirls formed using liquid fuels burning on a water surface. Here, it is shown that the water surface is not critical for a transition from a fire whirl to a blue whirl, but that the surface over which the whirl is formed must be flat without any obstructions to the incoming flow. This observation highlights the importance of the radial boundary layer formed at the base of the whirl. The transition therefore also occurs over a flat metal plate, over which temperature maps of blue whirls are obtained using thin-filament pyrometry. Visualization of the reaction front, by imaging spontaneous OH* chemiluminescence, shows that a significant fraction of the combustion occurs in the small, visibly bright, blue ring. The temperature maps are consistent with the burning structure seen with chemiluminescence, and they are qualitatively similar for blue whirls formed over both water and metal plates. High frame-rate images of the transition process show the presence of a recirculation zone within the flame. Together, these observations distinguish the blue whirl as a flame structure unique from the fire whirl and present a basis for understanding the physical processes which control blue whirl formation and its structure.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tohidi2018,

title = {Fire Whirls},

author = {Ali Tohidi and Michael J Gollner and Huahua Xiao},

doi = {10.1146/annurev-fluid-122316-045209},

issn = {0066-4189},

year  = {2018},

date = {2018-01-01},

journal = {Annual Review of Fluid Mechanics},

volume = {50},

number = {1},

pages = {187--213},

abstract = {Fire whirls present a powerful intensification of combustion, long studied in the fire research community because of the dangers they present during large urban and wildland fires. However, their destructive power has hidden many features of their formation, growth, and propagation. Therefore, most of what is known about fire whirls comes from scale modeling experiments in the laboratory. Both the methods of formation, which are dominated by wind and geometry, and the inner structure of the whirl, including velocity and temperature fields, have been studied at this scale. Quasi-steady fire whirls directly over a fuel source form the bulk of current experimental knowledge, although many other cases exist in nature. The structure of fire whirls has yet to be reliably measured at large scales; however, scaling laws have been relatively successful in modeling the conditions for formation from small to large scales. This review surveys the state of knowledge concerning the fluid dynamics of fire whirls, including the conditions for their formation, their structure, and the mechanisms that control their unique state. We highlight recent discoveries and survey potential avenues for future research, including using the properties of fire whirls for efficient remediation and energy generation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Xiao2016,

title = {From fire whirls to blue whirls and combustion with reduced pollution},

author = {H Xiao and M J Gollner and E S Oran},

doi = {10.1073/pnas.1605860113},

issn = {10916490},

year  = {2016},

date = {2016-01-01},

journal = {Proceedings of the National Academy of Sciences of the United States of America},

volume = {113},

number = {34},

abstract = {textcopyright 2016, National Academy of Sciences. All rights reserved. Fire whirls are powerful, spinning disasters for people and surroundings when they occur in large urban and wildland fires. Whereas fire whirls have been studied for fire-safety applications, previous research has yet to harness their potential burning efficiency for enhanced combustion. This article presents laboratory studies of fire whirls initiated as pool fires, but where the fuel sits on a water surface, suggesting the idea of exploiting the high efficiency of fire whirls for oil-spill remediation. We show the transition from a pool fire, to a fire whirl, and then to a previously unobserved state, a "blue whirl." A blue whirl is smaller, very stable, and burns completely blue as a hydrocarbon flame, indicating sootfree burning. The combination of fast mixing, intense swirl, and the water-surface boundary creates the conditions leading to nearly soot-free combustion. With the worldwide need to reduce emissions from both wanted and unwanted combustion, discovery of this state points to possible new pathways for reduced-emission combustion and fuel-spill cleanup. Because current methods to generate a stable vortex are difficult, we also propose that the blue whirl may serve as a research platform for fundamental studies of vortices and vortex breakdown in fluid mechanics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}