Greater Priority In Mind

U.S. Navy research project is fueled by Purdue's unique quiet wind tunnel

Greater Priority In Mind

Greater Priority In Mind

For Joseph Jewell, this is personal.

When he applied for the highly competitive Young Investigators Program through the Office of Naval Research, he had his grandfather, Charles "Chuck" Jewell, in mind.

Chuck Jewell was a chief petty officer in the U.S. Navy, serving overseas in World War II in the Pacific theater and stateside during the Korean War. Nearly 70 years later, Chuck Jewell's successors still are putting their lives on the line for the United States, specifically naval units in the Pacific. Only in the last decade or so has the Department of Defense ramped up its funding of hypersonic research, after it largely dried up after the Cold War. The resurgence was a necessary response to adversaries' advancements in high-speed flight technology.

Novel research to solve the unique problems presented in hypersonic research are of national importance.

Enter Jewell, an assistant professor in AAE, with that greater priority in mind.

Jewell was selected in May 2021 to receive a three-year, $600,000 grant from the Office of Naval Research for "detailed investigation of hypersonic instability, breakdown and natural transition under quiet flow with simulated ablation-gas injection." The research could provide a relevant and highly useful approach to visualize hypersonic flow fields, as well as a promising measurement for high-enthalpy or ablative flows that naturally produce carbon monoxide among other carbon-containing molecules.

When vehicles travel at hypersonic speeds through the atmosphere — at least five times the speed of sound — they undergo a process called "ablation" where, at high temperatures and high speeds, material vaporizes and erodes from the surface of the vehicle. The erosion happens as a complicated interaction between the surface and the aerodynamics. Understanding how that process happens is important: When a vehicle runs out of material to ablate away, it fails.

Jewell's research seeks a better understanding of ablation to predict the effects of it.

Because a lot of the heat shields and outer structure materials are carbon-based — carbon fiber, carbon woven or impregnated carbon — one of the main gases that tends to be created during ablation is carbon monoxide (CO). Though Jewell can't make ablation happen in the Boeing/AFOSR Mach 6 Quiet Tunnel — the flow is too cold — he will use a technique to measure CO injected through the surface of the wind tunnel model to simulate the process. He initially read about the technique as an application of the combustion industry with engineers designing an automotive or other internal combustion engine. In that process, CO is generally an indicator of incomplete combustion. In a typical combustion process, that's happening at fairly high pressures. But Jewell noticed that particular technique for detecting CO actually worked much better at lower pressures.

In a hypersonic wind tunnel, there are extremely low pressures.

"In theory, at least, we should be able to make better use of this technique or get a better picture from this technique than the people who actually came up with it and applied it for the first time to these combustion-type burning processes, flames and so on," Jewell said. "Because our tunnel, like essentially all hypersonic wind tunnels, is low pressure in the free stream. That's by design because at high altitude, the air is low pressure also. So it all scales."

Jewell's group will plumb the inside of the wind tunnel model with pipes attached to it to a tank of gas and inject the gas at controlled rates. The team will document what they're doing and then take pictures of the process. Essentially, it will be looking at the effects of the gas injection on boundary layer stability downstream.

Purdue's Mach 6 Quiet Tunnel is uniquely well-suited for the research, as it is the largest operational tunnel in the world able to produce low-disturbance flow.

"It's a technique that's been used in flames and burning processes, but no one has used it in a wind tunnel of any kind, as far as I know, let alone a hypersonic wind tunnel," Jewell said. "That's what I think particularly interested the Navy program manager who decided to fund the work.

"It's really a project that couldn't be done in the same way anywhere else but Purdue. So that's why I thought it made a good choice. I'm always looking for things that we can do that no one else can do. This was one of them."

Jewell will collaborate with other Purdue researchers. Terrence Meyer, a professor in Mechanical Engineering with a courtesy appointment in AAE, and ME Research Associate Professor Mikhail Slipchenko will assist on the research that includes a pulse-burst laser, and AAE Professors Sally Bane and Carson Slabaugh are offering use of some their equipment, such as high-speed cameras.

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