�Թ���

In a windowless, warehouse-sized lab on campus, a team of CU Boulder researchers huddle around two wind tunnels—long metal tubes that blow air currents at controlled speeds.

Laura Shannon, a graduate student in CU’s Paul M. Rady Department of Mechanical Engineering, turns a dial, releasing a hiss of gas that quickly ignites a burner inside one tunnel.

The crew turns out the overhead lights. The fire, glowing blue and yellow through a window in the tube, is the only light to be found. Shannon turns on the air current, speeding it up and slowing it down, and the flames flicker and sway wildly.

The researchers are using the wind tunnels to study wildfire behavior. For nearly a decade, the team has been delving into the hundreds of factors that can affect the way wildfire starts, moves and spreads, as well as the damage it causes.

Ultimately, the team has an ambitious goal: to build computational tools that can predict how wildfire will behave. They envision a day when, shortly after a fire starts, firefighters can plug in details about it and learn where—and how quickly—it could spread. The tools could help keep communities safer in a world where climate-driven wildfire is becoming more common—and more dangerous.

“Being able to have more accurate, better predictors of fires is extremely important to protecting people, lives and property,” said Shannon. “The more accurate we can make our simulations in the long run, the safer we can keep wildfires.”

The research team also brings a unique, interdisciplinary approach to studying wildfire, blending ideas and technology from mechanical and aerospace engineering.

“This research was driven by recognizing that there was a gap. There were these really advanced aerodynamics and sensing tools that had not been used in this field yet,” said Greg Rieker, a research team member and professor in the Paul M. Rady Department of Mechanical Engineering.

Teasing apart the elements of wildfire

Wildfire behavior is complex and hard to predict because there are so many variables—like wind, rain, humidity, fuel and topography—to consider. The researchers have been methodically isolating and studying these variables to understand more about how fire behaves under different conditions.

The team is using wind tunnels to better understand basics like how fire moves, its shape and structure, and how it transfers heat downstream. They’re also looking at the impact of ground slope on fire spread, using a tunnel that can tilt at an angle.

“The idea is to model the influence of ground slope to think about wildfires climbing hills versus descending. You have different physics and different dynamics,” said John Farnsworth, a team member and associate professor in CU’s Ann and H.J. Smead Department of Aerospace Engineering Sciences.

The team is also exploring how embers form and spread. Wind can carry these burning pieces of wood or debris miles away from a fire, sparking additional blazes. Embers were likely a major driver of the December 2021 Marshall Fire and the October 2020 East Troublesome Fire, which spread from Grand Lake to Estes Park overnight due to blowing embers.

A large smoke plume from the 2020 East Troublesome Fire in Grand and Larimer counties. Wind helped push the fire across the Continental Divide from Grand Lake to Estes Park, prompting massive evacuations. (Source: BLM)

In a study that has not yet been published, former mechanical engineering graduate student Charlie Callahan set one-millimeter wooden discs on fire to create embers, then dropped them into a wind tunnel and took a high-speed thermal video of the embers moving through the tunnel.

“Larger firebrands can travel long distances and start a fire a mile away, which causes fire spread. But also, small firebrands can change the rate of fire spreading over short distances,” Callahan said. “There hadn't been too many studies on looking at this specific size of firebrand.”

The study found that the embers, or firebrands, fluctuated rapidly in temperature—by hundreds of degrees—as they traveled through the tunnel. And the fluctuations happened more frequently in embers that were traveling at faster speeds compared to the wind speed. The faster they moved, the hotter they got.

Callahan and the other researchers plan to continue studying firebrands to understand more about the significance of these temperature changes and how they affect fire spread.

Looking forward

The researchers say it’s still extremely difficult for firefighters to predict how fires behave and spread, especially in areas with variable terrain and wind conditions. Fires such as the Marshall Fire and the East Troublesome Fire can spread more quickly and erratically than expected.

Scientists believe wildfire will likely become an even more significant threat as climate change progresses, temperatures rise and drought conditions persist in many areas. When fires happen, it’s crucial to be able to understand and predict how they’ll behave.

The work is particularly urgent for communities in the wildland-urban interface that border on wilderness and are more vulnerable to wildfire. The researchers hope their predictive tools might help improve evacuation plans and enhance firefighting approaches.

Peter Hamlington, a professor in the Paul M. Rady Department of Mechanical Engineering and the principal investigator behind this research, noted the impacts of wildfire extend beyond direct burn damage, and smoke from the fires can also travel long distances and negatively affect human health.

“A better understanding of the causes and dynamics of wildland fires will help us develop new computational tools for predicting the occurrence of fires and mitigating their most devastating effects,” Hamlington said.

“Ultimately, our project is focused on the development of more accurate and reliable predictive tools that can be used by those seeking to understand and reduce fire risk.”