“We can now easily experiment with different geometries for turbine blades,” said Guillermo Paniagua, Professor of Mechanical Engineering, whose research at Zucrow Labs focuses on turbines and propulsion. “We create 2D representations of an airfoil, put them in the water, instantly see the results, and then use that analysis to refine the airfoil design.”

Using water as an analog for supersonic flow is not a new idea; fluid mechanics researchers have been experimenting with this approach since the early 1950s. But as vehicles move faster and faster, testing them requires more elaborate and expensive facilities. So before his designs go into an expensive wind tunnel, Paniagua decided they first need to go back to basics. And to do that, he needed a water table.

In 2020, Paniagua welcomed Dr. Lukas B. Inhestern to campus as a postdoctoral Marie Curie Research Fellow. Inhestern had secured funding from the European Commission to investigate how shockwaves affect supersonic flow in turbine and compressor designs. His first step: supervising the design of the new water table.

“This was during the COVID era,” said Inhestern. “I collaborated remotely with a group of undergraduate Purdue students, who developed the CAD models as part of their senior design project. But at that point, they were just designs; they couldn’t meet in person to actually build it.”

At the time, Kevin Boes was an undergraduate student in Mechanical Engineering. “My older brother is a Purdue grad who did research with Dr. Paniagua,” said Boes, now a graduate research assistant in Paniagua’s lab. “I had just finished an internship with SpaceX and it got me excited to do actual aerospace research; Dr. Paniagua was the first person to come to mind. The first project he gave me was building this table.”

Using the CAD from Dr. Inhestern and his student team, Boes helped to source the parts and began the process of assembling the machine. “It was definitely a challenge,” said Boes, “But working through those issues, and learning project management along the way, was a great experience for me.”

The process of going from COVID-era CAD designs to a real functioning water table took more than two years.

Set the table

The facility consists of a 2-meter-square pane of glass, set at a gentle slope. A reservoir of water at the top end feeds a thin film of water over the entire face of the glass, emptying into another reservoir at the bottom. A series of pumps and tanks keeps the flow continuously circulating. “I had to learn more about plumbing than I realized!” said Boes.

Placing airfoil shapes on the glass interrupts the flow of the water, creating visual patterns that simulate what might be seen experimentally in a wind tunnel test, or simulated in a computer model.

But this water table has another trick up its sleeve. “Modeling continuous flow is one thing, but my project focuses on how shockwaves interact with turbines,” said Inhestern. “To model that, we needed a second part: a shockwave generator.”

Inhestern worked with another group of undergraduate Purdue students as part of their senior design project. They designed a secondary gantry to sit at the top of the 2-meter glass field, with a pulley-driven arm that moves horizontally from one side of the tank to the other. By lowering a pointer that barely breaks the surface of the water, the back-and-forth motion creates exactly the kind of shockwave that Inhestern wants to simulate.

The shockwave generator (right) simulates how shockwaves interact with the supersonic flows inside a turbine. (Purdue University photo/Jared Pike)

The advantages of this setup are obvious. “In comparison to wind tunnels, we offer the option to test quickly, and rapidly iterate your designs,” said Boes. “Imagine you remotely send your designs to us. We can 3D-print them, put them in the water table, and immediately give you experimental results that you can use to validate your computer simulations. That’s the vision for this facility.”

“This has really opened my eyes to all the great work going on here at Purdue,” said Boes. “Zucrow Labs is the largest academic propulsion lab in the world, and the research happening here is some of the best in the world. It’s great to be able to play a part in that.”

Bringing the water table to life was a group effort, led by (left to right) Dr. Lukas B. Inhestern, Dr. Guillermo Paniagua, and Kevin Boes. (Purdue University photo/Jared Pike)

Writer: Jared Pike, jaredpike@purdue.edu, 765-496-0374

Sources:
Guillermo Paniagua, gpaniagua@purdue.edu
Kevin Boes, boesk@purdue.edu
Lukas Inhestern, linheste@purdue.edu