Hypersonic Vehicle Analyses: The Needs and Challenges of Multidisciplinary Simulations

As a community, we are focused on improving the modeling of the chemistry of radiation ablation and structural response individually. In terms of coupling, we need to develop robust, flexible, and resilient approaches due to the different timescales and nature of information exchange. There is much research needed in this area. Many examples of multiphysics analysis exist that are of interest to us and others.

I would like to acknowledge the individuals who contributed to the results presented today, including my grad students Nick, Jenny, and Jens, as well as research staff at NSI and the AEROSPACE department. My colleagues KT and Jay also played a role in this work. Funding support from various sources made this research possible. If you have further questions beyond what we can address today, please feel free to reach out to me.

Thank you for your attention. I am now available to answer any questions. Thank you, Ian, for the excellent presentation. It generated several questions. I will go through them quickly to cover as much as possible.

We use flight data when available for validation, although there is less flight data compared to ground data. Flight testing in the hypersonic regime is challenging but essential for assessing our models.

The coupling of ablation products with the flow field, including gaseous and solid products, is a complex process. Surface heating is treated differently for the bulk of the surface and the chemistry happening instantaneously. We use thermodynamic equilibrium tables to predict the chemical species released due to surface chemistry and ablation. Most of the time, material removal occurs one atom or molecule at a time, with occasional chunks of material coming off in a process called spall. Ablation primarily occurs at the molecular level. Thermochemical equilibrium tables, known as B prime tables, are used, but an alternative approach involves finite rate surface chemistry to model surface processes. This approach considers different chemical compounds, reactions, and rates for surface processes, providing a more comprehensive method. Experimental data is crucial for determining surface rates, and progress is being made in developing models.

Turbulence chemistry interaction in hypersonics is a key question, especially in relation to ablation products and rough surfaces. While not currently under study, the broader community is exploring this area. The need for high fidelity experimental data is emphasized to improve the accuracy and confidence of results.

In analyzing constraint trajectories, the range limits are based on both drag differences and thermal constraints. The process involves iterating across subsystems for each time step of the unsteady process with ablation. Flow timescales are short, requiring convergence of computational fluid dynamics (CFD) to steady state, followed by time-discretized material response calculations. This staggered approach ensures fully coupled CFD and material response results.

Questions about inward turning inlets and fluid thermal structural interactions prompt discussions on the impact of 3D versus 2D inlets and the potential for damage evaluation from high cycle fatigue. Sensitivity analysis of quantities of interest (QOIs) to flow physics processes and the computational time required for aero thermos structural solutions are also considered. The continuum assumption is generally effective, but cases may require techniques like direct simulation Monte Carlo (DSMC) or molecular dynamics at very high altitudes. You might have to use DS MC for flying down a reentry trajectory from space. However, for most Hypersonic systems, the real action occurs in the continuum regime where there is maximum heating and aerodynamic loads. Gas-solid heterogeneous reactions can be limited to the ab blading surface or model porosity and reactions below the surface. This capability is useful for NASA and military applications with porous media and plying materials.

Regarding the old Sprint missile program data, there is ongoing work to explore old data vaults for valuable information to validate complex simulations. Digitizing and resurrecting old data could be incredibly valuable for current research efforts.

Ian's talk on the complexities of physics in Hypersonics and challenges in modeling and simulation was well received. The talk has been recorded and will be archived for those who registered. Questions can still be asked via text for the next 48 hours.

The next AIAA journal keynote will be on May 16, 2024, with Professor Marria J from the University of Texas at Austin discussing space environmentalism. It is a critical area for the future of humankind in space.

Thank you to Ian for the informative talk, Kevin for moderating, and all attendees for being part of the keynote. Have a wonderful day and thank you for joining.