Physics-Based Aerodynamic Simulation Models Suitable for Dynamic Behavior of Complex Bluff Body Configurations

The ability to accurately and rapidly predict tethered load instabilities and behavior is required if expensive flight test qualification flights are to be minimized. Tethered or slung loads are complex systems of systems, wherein the system and each constituent must be carefully classified, quantified, and modeled. A physics-based six degree-of-freedom simulation model, the Georgia Tech Aerodynamic Model for Bluff Bodies (GTABB), is under development, and has been adopted by the U.S. Army AMRDEC to support Army slung load simulations (FlightLab). An innovative feature of the GTABB model is that it can be informed using quasi-steady experimental test data, high-fidelity computations, or aerodynamic theory. This model is coupled with empirically-determined unsteady aerodynamic characteristics to provide a flexible, accurate, and extensible modeling and simulation framework. In this effort, unsteady aerodynamic refinements and computational cost reductions are demonstrated. A rigorous uncertainty quantification framework at both the system and component level, necessary for model certification, is established, along with examples. Model validation is extended to include correlations of full-scale flight test with a CONEX container, and comparisons with a complex configuration (truck) evaluated in a wind tunnel. The ramifications of predicting slung load behavior with and without helicopter degrees of freedom and wind are presented.