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The aerodynamic coefficients of the 7-cal. U.S. Army-Navy Spinner Rocket were characterized using computational fluid dynamic (CFD) calculations and validated using archival experimental data. The static aerodynamic coefficients, roll-damping, and pitch-damping moments were accurately predicted by steady-state Reynolds-averaged Navier-Stokes (RANS) as well as unsteady hybrid RANS/large-eddy simulation (LES) CFD. The Magnus moment was overpredicted in the subsonic and transonic regime. Unsteady RANS/LES computations did not improve the prediction of Magnus moment at the lower Mach numbers. Both steady-state RANS and unsteady RANS/LES simulations resulted in similar predictions of all aerodynamic coefficients. Distributions of Magnus moment along the projectile body showed that the largest difference in Magnus moment between configurations and Mach numbers was in the last caliber of the projectile body.
A computational fluid dynamics (CFD) approach to predicting high- speed aerodynamic flow fields of interest to the U.S. Army Research Laboratory (ARL) has been carried out The aerodynamic problems of particular interest are: (1) supersonic flow past the aftbody of projectiles with base mass injection, (2) supersonic flow past the M549 projectile, and (3) subsonic, transonic, and supersonic flow past an M864 projectile with base bleed and wake combustion. The commercially available FLUENT (Fluent, Inc. FLUENT. Version 5.1.1, Lebanon, NH, 1999.) CFD code was utilized. The computational effort supports an ongoing ARL- sponsored experimental investigation. Of particular interest in the present investigation is the careful characterization of the various turbulence models employed in the CFD code. Additionally, the ease of use and set-up as well as the computational time will be described. An experimental effort (Dutton, J. C., and A. L. Addy. 'Fluid Dynamic Mechanisms and Interactions Within Separated Flows'. U.S. Army Research Office Research Grant DAAH04-93-G-0226 and the Department of Mechanical and Industrial Engineering, University of illinois, Urbana-Champagne, Urbana, IL, August 1998.) consisting of detailed laser Doppler velocimeter (LDV), particle image velocimeter (PIV), and high-speed wall pressure measurements has been made in axisymmetric and planar subsonic and supersonic flows with embedded separated regions. The present work seeks to predict similar flow fields computationally and to address areas of agreement and disagreement.
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Computational fluid dynamic simulations (CFD) were used to predict the aerodynamic coefficients and flow field over a spinstabilized, 25-mm, sub-caliber training projectile. The primary objective of the investigation was to determine the CFD parameters necessary for the accurate prediction of the Magnus moment and roll damping of a spin-stabilized projectile. Archival experimental data was used to validate the numerical calculations. The Mach number range investigated was from 0.4 to 4.5. Steady state CFD calculations predicted the drag, normal force, pitching moment, and normal force center of pressure very well to within 10% of the experimental data. Time-accurate, detached-eddy simulations were found necessary to predict the Magnus moment in the subsonic and transonic flow regimes. Steady state CFD was found adequate to calculate the roll damping, which was predicted to within 15% of the experimental data in both steady state and time accurate calculations.
For future civil supersonic aircraft to have the operational flexibility offered by current subsonic aircraft, some means of reducing their sonic boom to acceptable levels is required. An effective technique by which the sonic boom ground signal may be altered, and potentially minimized, is through careful shaping of external features of the aircraft. By considering the detailed aircraft shape using nonlinear flow solvers, accurate assessments of sonic boom can be made during multi-disciplinary conceptual design optimization. Such capability would enable the development of aircraft satisfying not only a requirement on low boom, but also on the range of constraints and mission goals necessary to produce a viable aircraft design. This work presents a multi-level framework for the conceptual design of low sonic boom aircraft. The development of a robust, automated tool using output-driven mesh adaptation enables accurate prediction of sonic boom. Results are validated with available experimental data for a variety of signal forms. An approach combining linear supersonic potential theory with atmospheric propagation and loudness prediction methods is used to generate low-boom near-field signals subject to lift and equivalent area constraints. This signal generator is then used to build a response surface fit that enables a conceptual-level design optimization to develop aircraft configurations with low boom. The imposition of a diverse range of multi-disciplinary design constraints ensures a viable aircraft. Once a satisfactory baseline is obtained, the design is transferred to the CFD domain, where an adjoint-driven inverse design approach is used to determine the detailed aircraft shape. This optimization seeks to match the near-field pressure target associated with the conceptual baseline design, subject to geometric constraints that ensure conceptual-level performance predictions are preserved. An aircraft design example is presented, demonstrating the application of this approach on a supersonic business jet.