Four-story vertical wind tunnel installed within walls of Talbot Lab
A new, vertical wind tunnel was ingeniously installed inside the northwest corner of Talbot Laboratory on the University of Illinois Urbana-Champaign campus. It spans the building’s four stories, from the third floor to its basement. The largest of its kind, it has a total length of 15.2 meters, or just shy of 50 feet tall. A little more than 36 feet of the length, 11.2 meters, is a precision-made rectangular channel of constant cross-sectional area.
“The wind tunnel was specifically designed and built to study turbulent flows laden with particles, but it also enables fundamental research on wall-bounded turbulence and heat transfer effects,” said Laura Villafañe Roca, assistant professor in the Department of Aerospace Engineering who envisioned the project and led its design, construction, and installation.
The vertical tunnel shares a space with a large standpipe that supplies water to the fluids lab. Removing a manhole cover on each floor next to the standpipe, allowed for a straight shot installation from the third floor all the way to the basement.
“There is a blower near the top that drives the flow downward along the channel,” Villafañe said. “We can add particles into the flow through a screw feeder at the inlet. Changing the flow velocity changes the range of turbulence scales, the sizes and intensity of the eddies in the flow. Depending on the density and size, the particles have different inertia and interact differently with the turbulence.”
Villafañe said the tunnel was designed, built, and installed by her, her students, and aerospace staff members. All of the parts were fabricated in the Talbot Lab machine shop.
Manufacturing and building the tunnel posed multiple challenges. For example, it demanded precision machining the large pieces.
“It is very important that the inside surfaces are perfectly flat, highly polished, and with no discontinuity between sections that would affect the near wall flow and favor particle accumulation,” Villafañe said. “Every section has removable panels to allow cleaning access, and they all must fit back perfectly and ensure sealing so there is no leakage.
“This wind tunnel, this research tool, is versatile and highly modular,” Villafañe said. “You can vary the flow velocity by varying the rotational speed of the blower to about 4 to 30 meters per second resulting in Reynolds numbers between 13,000 and 82,000. You could also change the inside geometry of the tunnel by replacing the desired section, add surface roughness or other structures that affect the flow, or incorporate heating elements.
“For particle-laden flow research, the characteristics of the particles used, their feeding rate, and the inlet flow velocity are all experimental parameters that can be easily varied test-to-test to cover different regimes and discriminate the role of different key non-dimensional parameters,” she said.
Talbot Lab has a concrete crusher in the basement which sends a tremor through the building whenever tests are conducted. This anticipated vibration had to be considered in the design. At several points along the 50-foot span, special supports were added that allow the tunnel to move slightly in all directions, but not break.
“It is designed and installed so that it is isolated from the motion of the building,” Villafañe said. “Input from Professor James Phillips, who oversees testing on the 3-million-pound crusher, was instrumental.”
In addition to addressing the potential for shaking, there were a number of other challenges to overcome.
“The project called for extremely tight tolerances for the steps between the flanges,” said Dustin Burns, the aerospace engineering shop supervisor. “Each section was about a meter in length. When they were complete, we had to hand finish the steps. The material we used has a tolerance of plus or minus 4,000ths. We were looking for steps of less than a 1,000th of an inch in the seams. So, we had to hand fit each panel.
“Aligning the sections during the assembly was also a challenge,” Burns said. “It’s a big project. Physically, the pieces are big and with a tight tolerance so we couldn’t run it production style where you set one up and run 10 of them. The installation took two days. We had a chain hoist that hung from the top and stacked the sections all the way to the top of the building. I was on hand to monitor the safety of the project, but Professor Villafañe and her students did the work to level the flanges and ensure correct weight distribution at each level.”
About her research, Villafañe said “Most flows around us are turbulent and almost all carry particles on them. Tiny, massless particles, called tracers, can follow all flow fluctuations and remain randomly dispersed if fed that way. For particles that are much heavier compared to the flow, their trajectories are unaffected by turbulence. Anywhere in the middle, small inertial particles are segregated by the different turbulent eddies forming regions of particle clusters and voids. Preferential concentration of particles may alter the flow characteristics and affect other phenomena such as light or radiation transmission, reaction rates, deposition, etc.
“Whether we choose to ignore the effects of the particles or not depends on how important they are for a particular application. Volcanic ash and contaminants dispersion, dust ingested by engines, the distribution of reactants or heat inhibitors in a combustion system, are examples of particle-laden flows that would benefit from a better understanding of particle-turbulence interactions, predictive models and diagnostics.”
Villafañe hopes the facility will be used in collaborations with other agencies and institutions or for their own independent research.
“I have worked on similar, but smaller tunnels of less than 6 meters in length,” she said. “The size of this tunnel makes it one-of-a-kind. There may be one that compares in a private laboratory somewhere that I do not know about, but among the experimental research community, there is nothing else like this.”