Date of Award

3-2006

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Raymond C. Maple, PhD

Abstract

The complete numerical solution of the airflow around a store in extended free flight is of particular importance to the United States Air Force. Beggar is the primary Computational Fluid Dynamics (CFD) program used by the USAF to obtain solutions for store separations. However, Beggar's ability to simulate a store in free flight is limited because the store must fall through a static background mesh, eventually reaching a point where the solution will fail. The length of any free flight simulation is consequently limited by the height of the background mesh. Code modifications are made to Beggar to remove this requirement by pinning the store in the background mesh at its center of gravity. Rotations are accomplished within the background mesh, but translations are reflected as changes in the grid speeds of the background mesh. This allows the numerical simulation to continue indefinitely. Beggar's ability to model moving components (e.g. control surfaces) in multi-body problems is fully preserved. The modified code is applied to the MK-84 AIR model, which demonstrates that the solution of a pinned store using the modified code adequately matches the solution of a translating store using the unmodified code. In addition, extended free flight simulations are conducted in which the dynamic behavior and long term trajectory of the store are observed. The longest simulation lasts for 135 seconds of solution time. Testing of a generic store body with multiple moving fins results in good agreement between the unmodified and modified solution methods. The modified code reduces overall computational cost by 17% for simulations of similar length because of the smaller background mesh. The combination of indefinite runtime and control surface modeling will make Beggar a powerful tool for studying the non-linear dynamic behavior of stores in free flight.

AFIT Designator

AFIT-GAE-ENY-06-M02

DTIC Accession Number

ADA449429

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