Unsteady Aerodynamic Uncertainty Quantification of a Blunt-Body Entry Vehicle in Free-Flight

Thumbnail Image
Willier, Brenton J.
Hickey, Alexandra M.
Robertson, Bradford E.
Mavris, Dimitri N.
Associated Organization(s)
Supplementary to
The design process of blunt-body entry vehicles balances atmospheric heating and drag to ensure crucial payloads can safely traverse through entry, descent, and landing. However, the blunt shape leads to a chaotic recirculating wake. Currently, uncertainties in the vehicle design process are captured through scalars and multipliers, and these conservative estimations lead to over-engineered vehicles, reduced payload capacity, and less accurate landings. To supplement the data gathered through physical testing, CFD-in-the-loop free-flight trajectories can be simulated throughout the flight regime. While CFD performance has improved significantly, the number of cases required to produce a meaningful sample for an uncertainty analysis remains computationally intense. Parametric uncertainty can be captured with traditional uncertainty methods like Monte Carlo analysis. However, the non-parametric uncertainty due to the unsteady nature of the chaotic wake has yet to be studied for free-flight analysis. This paper presents and implements an ensemble sampling initialization approach to determine the impact of unsteady wake structures imparted on CFD-in-the-loop data produced using replicated trajectory simulations. To enable this data generation, the Genesis vehicle gridding process is detailed, along with an overview of the free-flight CFD simulation setup for a supersonic flight regime. While running a static unsteady simulation, ten flow fields were saved at various times to capture different instantaneous structures in the wake. After initializing identical free-flight simulations with the ten different flow fields, results of vehicle aerodynamic angles, aerodynamic force and moment coefficients, inertial velocity, and vehicle trajectory in multiple reference frames showed identifiable trends with diverging behavior. The uncertainty on these variables due to unsteady flow is also quantified throughout the motion. It is concluded that this aspect of uncertainty must be carefully considered when CFD-in-the-loop is used to model the flight characteristics of a blunt-body vehicle.
NASA Early Stage Innovations grant 80NSSC23K0229
Date Issued
Resource Type
Resource Subtype
Rights Statement
Rights URI