The 1998 Version Of The Nswc Aeroprediction Code
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The 1998 Version of the NSWC Aeroprediction Code
The NSWC Aero prediction code has been extended to the roll position of 45 deg (fins in 'x' or cross roll orientation) in addition to the roll position of 0 deg (fins in '+' or plus roll orientation). It has also been extended to compute aerodynamics of nonaxisymmetric bodies based on an equivalent axisymmetric body. In addition, the nonlinear aerodynamic loads have been distributed over the body and lifting surfaces to provide a more useful tool for preliminary structural analysis. Finally, new technology was developed to improve the prediction of axial force at angle of attack (AOA). These new technologies have been integrated into the AP95 and will be transitioned to legitimate users as the AP98. To make the AP98 more user friendly, an upgraded pre- and post-processing, personal computer interface was also developed. Comparisons of the new theory have been made to both experimental data and the AP95. Comparisons of theory and experiment show the AP98 to be at least as good as the AP95 and, in general, maybe slightly better. In general, average accuracy levels of aerodynamics are +/- 10 percent on axial and normal force and +/- 4 percent of body length on center of pressure. For nonaxisymmetric body cases, accuracy can be slightly higher than these numbers, although not enough cases have been considered to make a definitive assessment. While these accuracy levels are encouraging for a semiempirical code, they could be improved upon by use of computational fluid dynamics codes or additional experimental data or both to reduce errors due to limited data bases.
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.
User's Guide for an Interactive Personal Computer Interface for the 1998 Aeroprediction Code (AP98)
This report describes interactive, user friendly, pre-processing and post-processing personal computer (P.C.) modules designed to operate with the latest version of the Naval Surface Warfare Center (NSWC) Aeroprediction Code (AP98). As part of the preprocessing input module, geometry inputs are automated by giving the user many options. By using this new software, a set of aerodynamic coefficients can be obtained on most weapon configurations in less than 15 minutes from time of initial setup to computer outputs, compared to 2-4 hours for the AP98 computer mainframe version, While the computer cost savings are modest (the AP98 executes on a large computer in less than a second), the manpower savings and productivity enhancements can be significant. Various plots of the aerodynamic coefficients are available to the user and are plotted automatically by the post-processing module. Data output is also made available to the user in the form of standard Aeroprediction output files as well as tabulated data. The User's Guide is designed to aid users of the AP98 by correlating AP98 P.C. Interface Data Inputs and the corresponding source code variable names.