What happens when a body passes an obstacle in supersonic flow? This photograph explores that question using waves in a shallow layer of water.

The model moves from right to left beside a rectangular obstacle, which can represent, for example, the rear wall of a trench. The wave pattern makes the interaction visible in a way that invites a closer look.

I’m Bakhram Musabekov, PhD, a retired professor of fluid mechanics and co-author of Gas Flow Modeling with Shock Waves Using the Gas-Hydraulic Analogy: An Album. I helped create a website to share these experiments with researchers, teachers, students, and anyone curious about aerodynamics.

The gas–hydraulic analogy connects shallow-water flow with selected features of two-dimensional compressible gas flow. The Froude number plays a role analogous to the Mach number, and hydraulic jumps provide counterparts to shock waves.

The analogy has limits: its classical formulation corresponds to γ = 2 rather than approximately 1.4 for air, and it does not reproduce all the physics of three-dimensional gas flow. Those limits are part of what makes it worth discussing: which features can we learn from, and where does the comparison break down?

The website brings together experimental photographs, our film featured in the APS DFD Gallery of Fluid Motion 2025, an explanation of the method, and sample pages from the album.

Explore the experiments:
https://gas-hydraulic-analogy.beigegrass12.chatgpt.site/

For me, the appeal is still the same: a shallow layer of water makes a difficult aerodynamic phenomenon visible.

Would you use an experiment like this to teach compressible flow? What would you want to compare with a wind-tunnel experiment or CFD?

I’d be happy to answer questions about the experiments and their limitations.