The 2002 Version Of The Aeroprediction Code
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The 2002 Version of the Aeroprediction Code
A new version of the aeroprediction code (APC), the AP02, has been developed to address the requirements arising from advanced weapon concepts. The AP02 was formed by adding significant new technology and several productivity improvements to the previous version of the APC, the AP98. New technology added included 6 and 8 fin aerodynamics, improved nonlinear aerodynamics, improved pitch damping predictions, improved power-on base drag estimates, base-bleed effect on base drag estimation, improved axial force of nonaxisymmetric bodies and trailing-edge flap capability. Other improvements and productivity enhancements include an aerodynamic smoother, ballistic and three degree-of-freedom simulation modules as well as refinements for the pre- and post-processor for inputs and outputs of the AP02. Comparison of the predicted aerodynamics of the AP02 to AP98 and experimental data showed the AP02 to be slightly better than the AP98 in most cases that both codes would handle. However, due to the additional new technology incorporated into the AP02, many new options are available in the AP02 that are not available in the AP98. Therefore, the AP02 is more robust and, on average, is slightly more accurate than the AP98 in predicting aerodynamics of weapons.
Improvements in Pitch Damping for the Aeroprediction Code with Particular Emphasis on Flare Configurations
New capability has been added to the NSWC aeroprediction code to allow aerodynamics to be predicted for Mach numbers up to 20 for configurations with flares. This new capability includes extending the static aerodynamic predictions for Mach numbers less than 1.2, improving the body alone pitch damping for Mach numbers above 2.0, and developing a new capability for pitch damping of flared configurations at Mach numbers up to 20. This new capability for flared configurations was validated for several different configurations in the Mach number range of 2 to 8.8. In general, pitch damping predictions of the improved capability was within 20 percent of either experimental data or computational fluid dynamics calculations. This accuracy level is believed to be quite adequate for dynamic derivatives in the preliminary design stage. These new additions to the aeroprediction code will be transitioned to users as part of the 2002 version of the code (APO2).
Improved Power-on, Base Drag Methodology for the Aeroprediction Code
Improved methods for base pressure prediction under base bleed and rocket motor-on conditions have been developed. The base bleed method makes several refinements to the method developed by Danberg at the Army Research Laboratory in Aberdeen, Maryland. The improved rocket motor-on, base pressure prediction improves upon the method developed at the Army Missile Command in Huntsville, Alabama by Brazzel and some of his colleagues. The major refinement to the base bleed method of Danberg was to estimate the power-off value of base pressure empirically based on an extensive data base, as opposed to using computational fluid dynamics codes to predict this term. The major modifications to the power-on base pressure prediction method of Brazzel was to extend its range of applicability to high values of thrust coefficient, to Mach numbers less than 1.5, and to different afterbody shapes. In comparing the improved methods for power-on base drag prediction to experiment, it was seen that both methods gave reasonable agreement to most experimental data bases. However, more validation is needed, particularly for the combined effects of angle of attack, fins, and power-on conditions.