Millimeter-wave tomographic imaging of particle-laden flows in planetary landings

This thesis presents the development of millimeter-wave tomographic interferometry, a novel method for measuring absolute particle concentrations in opaque dispersed multiphase flows, and its application to planetary plume-surface interactions as a demonstration case. The advantages of millimeter-wave tomographic interferometry over state-of-the-art opaque flow measurement techniques include: the ability to penetrate dense particles clouds with minimal transmission loss compared to optical radiation (i.e., near-visible light), a linear response to volume fraction that is mostly independent of particle properties, the use of safe non-ionizing radiation, kilohertz sampling rates, and compact low-cost hardware. Spatial resolution is the main limiting factor of the technique when sub-wavelength resolution is required. In this thesis, we compare two methods to calibrate a millimeter-wave radar interferometer for absolute concentration measurements: a direct method that uses known particle concentrations, and an indirect method that relies on measuring the relative permittivity of bulk particle samples. Results from both calibration methods agree within 0.7 % when using the Lichtenecker logarithmic effective medium equation. The agreement between the two independent calibration procedures validates the theoretical framework of millimeter-wave tomographic interferometry. Furthermore, we systematically account for the various sources of errors on the measurement, including secondary reflections, internal radar noise, and finite spatial resolution. We use Monte Carlo simulations to quantify the error amplification caused by the tomographic reconstruction process and synthesize these findings into an overall error budget identifying dominant error sources under representative experimental conditions, with path-integrated measurement errors of -22 dB and reconstruction errors of -9 dB. Finally, we explore the ejecta dynamics of Plume-Surface Interactions (PSI) using millimeter-wave tomographic interferometry. We achieved the first quantitative mapping of ejecta concentrations in PSI experiments, overcoming the limitations of conventional optical methods hindered by the opacity of ejecta clouds. Our experimental setup is a Mach 5 jet impinging on a bed of regolith within a vacuum chamber, simulating planetary landing scenarios. We characterize the PSI phenomenology across different ambient pressure levels, nozzle altitude, and jet mass flow rate. Our results reveal the existence of two cratering regime in our dataset: shallow cratering, in which material is removed from the surface by viscous shear, parallel to the surface, and deep cratering, in which diffusion-driven erosion and bearing capacity failure appear to be the driving forces. The techniques presented in this thesis are mature, and the detailed information they provide paves the way towards an improved understanding of PSI physics. They can be readily applied to any opaque particle-laden gas flow, with possible areas of applications in meteorology, fire safety, fuel sprays, and industrial powder handling.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Rasmont, Nicolas Gerard Emmanuel

Contributors dc:contributor

• Villafane-Roca, Laura
• Rovey, Joshua L
• Bernhard, Jennifer T
• Elliott, Gregory S

• multiphase flow
• millimeter-wave
• radar
• interferometry
• plume-surface interactions

Statement dc:rights

• © 2025 Nicolas Gerard Emmanuel Rasmont

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129600

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129600