Abhishek
Subedi

Coefficient of drag in particle-laden supersonic flow

Advisor: Dr. Omid Amili · Fluids and Imaging Innovation Lab

How hard does a supersonic jet push on a solid particle? I'm measuring that drag inside the shock cells of an underexpanded jet, on a jet rig my team and I built at the Fluids and Imaging Innovation Lab.

The problem

The drag coefficient of a solid particle in supersonic flow is not settled: the correlations in general use disagree by a factor of two at the conditions that matter for solid rocket propulsion, cold-spray deposition, and high-speed particulate transport, and nearly all the data behind them come from shock tubes and ballistic ranges. My thesis measures drag in the complementary configuration, the quasi-steady shock-cell field of an underexpanded supersonic jet.

Facility & imaging

My team and I at the Fluids and Imaging Innovation Lab designed and built the facility: a 5.08 mm converging nozzle fed through a conditioned settling chamber. I developed its LabVIEW data acquisition and control system for pressure and temperature instrumentation, valve sequencing, and safety interlocks. A Z-type schlieren system images the jet at 34,035 frames per second, resolving the shock train and the silhouettes of individual beads at the same time. The shock-cell spacing, measured from the images by autocorrelation, fixes the gas state (fully expanded Mach number 1.60, 447 m/s), and a Python particle-tracking pipeline turns each bead into a nozzle-referenced velocity and acceleration history.

Analysis ongoing

Because one track gives one equation for several unknown forces, I am separating the non-drag terms experimentally: regressing acceleration on 1/d_p across particles of different size splits it into a drag group and a size-independent pressure-gradient group. The drag-coefficient analysis is ongoing, at particle Reynolds numbers of roughly 20,000 to 40,000, and will be compared against the Henderson, Loth et al., and Clift–Gauvin correlations.

Jet Mach number

1.60

Particle Reynolds no.

20k–40k

Imaging rate

34 kfps

Nozzle exit

5.08 mm

Talk at the 78th Annual Meeting of the APS Division of Fluid Dynamics (2025) on the development of open-loop supersonic jet rig facilities. Poster at the MEANES 2026 Ted Keith Distinguished Event Poster Session. The high-speed footage also became Riding the Shock Train, a short film prepared for the APS Gallery of Fluid Motion 2026.