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Projecte llegit

Títol: DSMC Study of Gas-Surface Interaction Effects on VLEO Aerothermodynamics

Estudiants que han llegit aquest projecte:

Director/a: ALTMEYER, SEBASTIÁN ANDREAS

Departament: FIS

Títol: DSMC Study of Gas-Surface Interaction Effects on VLEO Aerothermodynamics

Data inici oferta: 20-12-2025     Data finalització oferta: 20-07-2026


Estudis d'assignació del projecte:
    MU AEROSPACE S&T 21
    MU AI4CI
    MU DRONS
    MU EM CODAS 1
    MU EM CODAS 2
    MU MASTEAM 2015
Tipus: Individual
 
Lloc de realització: EETAC
 
Paraules clau:
Direct Simulation Monte Carlo, rarefied gas dynamics, transitional flow, Knudsen number, gas-surface interaction, Very Low Earth Orbit, VLEO aerothermodynamics, flat-plate aerodynamics, wall-scattering models, SPARTA
 
Descripció del contingut i pla d'activitats:
This thesis will investigate the aero-thermodynamics of a flat plate (representing solar panels, drag sails, or aircraft surfaces) in rarefied and transitional flow regimes using the Direct Simulation Monte Carlo (DSMC) method. As satellites operate in Very Low Earth Orbit (VLEO), traditional
continuum assumptions break down, and aerodynamic forces and surface heat fluxes start to depend a lot on molecular gas-surface interactions. The study will take a canonical inclined
flat plate geometry, making it directly relevant to VLEO drag and thermal-load prediction. Simulations will be performed using the open-source DSMC solver called SPARTA or similar. Critical parameters will be studied, in pariticula applied force, momentum-flux, and heat-flux and their outputs across increasing Knudsen number will be analyzed. A key goal will be the investigation how the results vary between modelling methods
when predicting aerodynamic loads for gas-surface interaction (GSI). Main focus will lie on Maxwell and Cercignani-Lampis-Lord (CLL) scattering laws and accommodation coefficients. The work
will include systematic verification through particle-number and sampling-time convergence and cross-validation against published DSMC benchmark results, which will copy the conditions of
beforehand.
The required software tools for the project are Matlab, Python, and SPARTA carry out the implementation and simulations.
 
Overview (resum en anglès):
Very Low Earth Orbit (VLEO) is attractive for Earth-observation and fast-response space missions, but spacecraft operating at these altitudes are exposed to rarefied flow, from slip to high-Knudsen-number transitional conditions, in which aerodynamic loads and surface heat transfer depend strongly on gas-surface interaction (GSI) modelling. This thesis investigates how wall-scattering assumptions affect VLEO-relevant flat-plate aerothermodynamics using the Direct Simulation Monte Carlo (DSMC) method. Simulations were performed in SPARTA for the inclined flat-plate benchmark of Dogra et al., using a zero-thickness plate of length 1 m at an incidence angle of 40 degrees, wall temperature of 1000 K, freestream speed of 7.5 km s-1, and freestream Knudsen numbers of 0.023, 0.137, 3.146, and 8.439. The fully diffuse Maxwell wall model was used as the benchmark anchor, after which Maxwell and Cercignani-Lampis-Lord (CLL) wall models were compared under identical freestream, catalytic wall-treatment, and sampling choices. A prescribed surface-emission branch with an emission-to-incidence number-flux ratio of 1.0 was also included as a secondary boundary-condition sensitivity, representing an idealised outgassing-like perturbation.

Numerical credibility was addressed through DSMC resolution checks, stationary-window selection, correlated block averaging, confidence-interval reporting, and explicit treatment of digitised-reference uncertainty. The reproduced fully diffuse baseline captured the main Dogra trends. Drag was reproduced most consistently, with errors within about 4.5% across all cases and within 2% for three of the four Knudsen numbers. Compression-side surface distributions also showed strong curve agreement, with reported NRMSE and NMAE values below approximately 0.07.

The main result is that GSI modelling is a first-order component of rarefied flat-plate aerothermodynamics. Reducing Maxwell accommodation reduces skin friction and heat transfer, strengthens the high-rarefaction pressure response, and drives the specular limit toward an L/D value approximately equal to the cotangent of 40 degrees. At the highest Knudsen number of 8.439, the fully specular Maxwell case increased CL by +617.47% and L/D by +800.65% relative to the fully diffuse baseline, while reducing CD by -20.34%. The CLL cases showed that normal and tangential accommodation are not interchangeable: low normal accommodation mainly strengthens pressure loading, whereas low tangential accommodation suppresses shear and can also reduce pressure indirectly through residence-time and near-wall redistribution effects as rarefaction decreases. Consequently, similar CL values can arise from different combinations of pressure loading and shear reduction, leading to substantially different CD and L/D responses.

The prescribed-emission branch remained secondary to the wall-scattering sensitivity. Its effect was negligible at the two lowest Knudsen numbers, but became measurable at hig

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