A time accurate fluid-structure interaction framework using a Cartesian grid CFD solver
Bopp, Matthew Scott
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The landing of the Mars Science Laboratory (MSL) in 2012 demonstrated the limits of supersonic planetary entry technology through the use of a disk-gap-band parachute deployed from behind the aeroshell capsule. With the eventual goal of sending humans to Mars, the payload requirements are estimated to increase by a factor of 40, far outside the current technological envelope. With a density of less than 1% of Earth's, the Martian atmosphere makes the task of generating aerodynamic drag very challenging. Larger aeroshells produce more drag, but the vehicle is then too large to fit as payload inside a rocket. By utilizing inflatable aerodynamic decelerators, the drag area can be significantly increased, while the pre-deployed configuration has high packing efficiency. New technologies bring with them the requirement to study their behavior, and characterize their flight limits. Wind tunnel tests are difficult due scaling concerns, and flight tests are costly and time consuming. Thus, accurate computational modeling of the fluid-structure interactions (FSI) is critical in the development of aerodynamic decelerators. Much of the current research in FSI focuses on high fidelity analysis, which is often very computationally expensive, and requires significant user intervention. The current work fills a niche where the analysis time and human interaction is reduced, by utilizing an adaptive, Cartesian grid framework for solving the computational fluid dynamics (CFD). A time accurate, partitioned coupling strategy is employed to study FSI applied to flexible materials under high dynamic pressure loads. The structural dynamics is solved using LS-DYNA, and care must be taken at the interface boundary conditions to reduce numerical errors. The development of this tool has relied on a complete re-write of the in-house CFD code, NASCART-GT, where significant improvements have been made in computational efficiency and scalability. CFD simulations with prescribed motions are studied in order to validate the fluid dynamics of high speed flows with non-stationary boundary conditions, and to study the effects of solution-based grid adaption for these simulations. The interaction with rigid body dynamics is presented in simulations of the free flight dynamics of the MSL capsule. FSI simulations are then presented for a series of test cases, where the physics is validated for the unsteady, time accurate coupling of 1-D piston motion and 2-D beam deformation. Finally, steady state and time accurate simulations of an inflatable aerodynamic decelerator demonstrate the effectiveness of the current methodology in furthering the development of decelerator technologies.