Implementation and Assessment of a Time-Accurate Aeroelastic Model for Analysis of Inflatable Aerodynamic Decelerators

The landing of the Mars Science Laboratory (MSL) in August 2012, demonstrated the limits of planetary entry technology. Since the 1970s, the disk-gap-band (DGB) parachute has been used on nearly all Mars entry missions as a means to decelerate from supersonic Mach numbers. As the landed payload mass has continued to increase, so has the size of the parachute. However, at the current, and future mission requirements for landed mass, there is no qualification data on the effectiveness of the DGB. This becomes especially critical in low density atmospheres such as the one surrounding Mars, where the atmosphere is less than 2% the density of Earth’s. As payloads continue to increase in mass, further investigations are required for continued use of traditional parachutes. Currently, novel concepts are being investigated by researchers, where the drag area of the entry vehicle is increased through the use of inflatable or mechanically deployable devices. As these devices continue to grow in size, wind tunnel tests become increasingly difficult due to scaling concerns. Additionally, flight testing all candidate designs and configurations is very costly and time consuming. Thus, an efficient computational methodology can fill this gap. The physical problem under investigation is that of fluid-structure interactions (FSI) applied to flexible materials under high dynamic pressure loads. The proposed work aims develop a time-accurate aeroelastic tool to model the FSI of inflatable decelerators. A partitioned-coupling methodology is applied, where an unstructured, Cartesian fluid solver, and a stand-alone structural solver are connected through a data mapping process. Much of the current research in FSI focuses on high fidelity analysis, which is often very computationally expensive and requires significant user intervention. The proposed work attempts to fill a niche where the analysis time and human interaction is reduced. Such an approach is highly desirable during the design process of new configurations. In order to achieve these goals, significant upgrades have been made to the current in-house CFD tool, NASCART-GT. The software has been completely re-written using a modern object oriented approach in C++, with emphasis on performance, scalability, maintainability, and efficient use of external libraries where appropriate. CFD verifications and validations are included, with emphasis on moving-body simulations. Static FSI coupling is investigated for simulations where the time history is not critical, and their exists a steady-state solution. The culmination of the work will include time accurate simulations of one and two dimensional flow configurations, as well as a 3-D simulation of a relevant deployable decelerator. The goal of the fellowship was to investigate aeroelastic coupling for various inflatable aerodynamic decelerator (IAD) configurations via computational methods. The developed tool aims to provide a framework for coupling a computational fluid dynamics solver with an appropriate finite element tool to perform unsteady, time-accurate analyses. The intent is to apply this FSI capability to configurations that have or will be tested in ground-based facilities or flight tests. The research described in this document was performed with one primary goal. The objective was to develop a computational tool capable of analyzing unsteady FSI problems pertinent to planetary entry configurations. Significant progress has been made towards achieving this goal. The partitioned coupling approach has provided a flexible framework for interfacing the CFD and FEA software. The use of the Cartesian grid framework has provided an efficient methodology that can be used as a mid-fidelity analysis tool when exploring the design space of an entry configuration. The first step in this direction was to validate a newly written fluid dynamics solver for the current applications. Second, the development of prescribed rigid body motion within the current framework aimed at validating the physics associated with moving surfaces through a stationary unstructured Cartesian mesh. Two cases have been presented in this document, including the motion of a supersonic piston and the oscillatory motion of a transonic NACA 0012 airfoil. The piston analysis provided a framework for investigating the accuracy of moving body simulations when compared to an analogous, stationary simulation only differing in reference frame. The oscillating airfoil simulation provided a validation for the normal force characteristics associated with unsteady flow. Next, a 2-D version of the MSL capsule was used to validate static simulations against an industry validated CFD tool. A simulation was presented, demonstrating the coupling with rigid body dynamics, referred to as free flight simulations. The 2-D analysis has laid the groundwork for the continued development and validation of the 3-D version to be compared against ballistic range data. The FSI capabilities were first analyzed by investigating the steady state deflection of a semi-rigid tension cone. This case provided a means for validating the coupling between fluid dynamics and structural dynamics where time accuracy is irrelevant. The final three unsteady FSI cases described the remaining future work to be completed. These cases were broken down into 1-D, 2-D, and 3-D problems. This provides an efficient methodology for the validation of the tool. Upon completion of these remaining items, the developed tool will provide a means for studying time accurate unsteady FSI flows for planetary entry configurations.