Research
Current Projects:
Advanced Computational Center for Entry System Simulation (ACCESS)
The objective of this project is to revolutionize analysis and design of planetary entry systems through the development of fully integrated simulation framework. The Macdonald group is working in the areas of gas-phase chemistry modeling and turbulence/transition modeling. We are seeking to understand the transition mechanisms on hypersonic blunt body flows, improve the prediction of hypersonic turbulent flows using wall-modeled large eddy simulation, and improve chemical kinetic modeling for systems and atmospheres of interest to NASA.
Papers:
C1. Braga, M. A., Macdonald, R. L., "A Study of Hypersonic Blunt Bodies With Roughness Using WRLES," AIAA SciTech Forum 2025, Orlando, FL. https://doi.org/10.2514/6.2025-2747
C2. Macdonald, R. L., "Non-Equilibrium Kinetics of C + N2 for Titan Entry Applications," AIAA Aviation Forum 2024, Las Vegas, NV, 2024. https://doi.org/10.2514/6.2024-3648
C3. Braga, M. A., Dungan, S., Brehm, C., Macdonald, R. L., "Numerical Simulation of Boundary Layer Transition on Mach 6 Cylinder with Randomly Phase Sinusoidal Roughness," AIAA SCITECH Forum 2024, Orlando, FL, 2024. https://doi.org/10.2514/6.2024-1976
This project is funded by NASA Space Technology Research Institutes Program (https://www.access-nstri.org/).
High-fidelity modeling of non-equilibrium gas-phase recombination for hypersonic air flows
Hypersonic flows are generally characterized by strong shock waves, which generate high-temperatures in the shock layer. However, generally the surfaces do not heat up as quickly as the surrounding gas, and as the gas approaches the surface, the temperature drops. In this near wall region, temperature gradients trigger recombination reactions (where atoms recombine into molecules) which may occur in non-equilibrium. The aim of this project is to develop a model for the recombination process in rapidly cooled air flows.
Papers:
J1. Ravichandran, S., Macdonald, R. L., "State-to-State Oxygen and Nitrogen Recombination Rates Computed Using Selectively Sampled Quasiclassical Trajectories.” Journal of Thermophysics and Heat Transfer. 0, 0:0 (2025). https://doi.org/10.2514/1.T7216
C1. Ravichandran, S., Macdonald, R. L., "Compressible Laminar Locally Self-Similar Boundary Layers in Thermochemical Nonequilibrium," AIAA SciTech Forum 2026, Orlando, FL. https://doi.org/10.2514/6.2026-2061
C2. Ravichandran, S., Macdonald, R. L., "Accelerated Molecular Dynamics-Based Gas-Phase Recombination Rate Coefficients for O3," AIAA Aviation Forum 2024, Las Vegas, NV, 2024. https://doi.org/10.2514/6.2024-3649
This project is funded by the Air Force Office of Scientific Research (AFOSR) Young Investigator Program (YIP).
Development of Validated Hypersonic Plasma Kinetics Models Including Atomic Excitation
Understanding the initial generation of plasma for hypersonic flows is critical to predicting phenomena such as communications blackout. However, recent work by Boyd and Josyula (JTHT, 2021) has shown that excited atomic states are expected to play a significant role in the associative ioniziation process, one of the first mechanisms to generate electrons in the flowfield. The goal of this work is to develop a model for the initial generation of plasma using a combination of experiments, ab initio calculations, and reduced order models. This work is in collaboration with Drs. Boyd (CU-Boulder), Adamovich (Ohio State University), Guo (University of New Mexico), Hanson (Stanford University), and Minton (CU-Boulder).
Papers:
C1. Rodriguez, L. F., Macdonald, R. L., Aiken, T. T., Boyd, I. D., "Assessment of QCT-Master Equation Informed Chemical Kinetic Parameters for the O2+N Interaction in a Two-Temperature Mode," AIAA SciTech Forum 2026, Orlando, FL. https://doi.org/10.2514/6.2026-2803
C2. Rodriguez, L., Macdonald, R. L., "Rovibrational-Specific Kinetics Database and Master Equations Study on NO(X2Π)+O(3P) and O2(3Σ−g )+N(4S) Systems," AIAA SciTech Forum 2025, Orlando, FL, 2025. https://doi.org/10.2514/6.2025-2341
This project is funded by the Office of Naval Research (ONR) Multi-University Research Initiatives (MURI) Program.
Wall modeled large eddy simulation of high-enthalpy hypersonic flows
Hypersonic entry vehicles such as capsules operate in an extreme environment where a plethora of physical phenomena must be understood and modeled to design thermal protection systems. Among these phenomena, the interaction between turbulence and chemical reactions in the gas is generally not well understood. This work will extend wall-modeled large eddy simulations (WMLES) to incorporate chemically reacting effects, enabling scale resolved simulations of chemically reacting turbulent flows. WMLES is attractive approach to turbulence modeling for hypersonic flows because it relies on fewer modeling assumptions than Reynolds Averaged Navier-Stokes (RANS), the current design paradigm, at a tractable computational cost not afforded by traditional LES. This work will advance our fundamental understanding of hypersonic chemically reacting flows and enable future improvements to the RANS models currently in use for spacecraft design.
Papers:
C1. Camp, J., Simon, J., Braga, M. A., Macdonald, R. L., "Two Temperature Wall Model for High Enthalpy Hypersonic Large Eddy Simulation," AIAA SciTech Forum 2025, Orlando, FL. https://doi.org/10.2514/6.2025-2576
This project is funded by NASA Early Career Faculty (ECF) Award.