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  • 1
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    Increased ephemeris accuracy using attitude-dependent aerodynamic force coefficients for inertially stabilized spacecraft (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The FREEMAC program used to generate the aerodynamic coefficients, as well as associated routines that allow the results to be used in other software is described. These capabilities are applied in two numerical examples to the short-term orbit prediction of the Gamma Ray Observatory (GRO) and Hubble Space Telescope (HST) spacecraft. Predictions using attitude-dependent aerodynamic coefficients were made on a modified version of the PC-based Ephemeris Generation Program (EPHGEN) and were compared to definitive orbit solutions obtained from actual tracking data. The numerical results show improvement in the predicted semi-major axis and along-track positions that would seem to be worth the added computational effort. Finally, other orbit and attitude analysis applications are noted that could profit from using FREEMAC-calculated aerodynamic coefficients, including orbital lifetime studies, orbit determination methods, attitude dynamics simulators, and spacecraft control system component sizing.
    Keywords: AERODYNAMICS
    Type: Flight Mechanics(Estimation Theory Symposium, 1991; p 249-264
    Format: application/pdf
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  • 2
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    Developments and trends in three-dimensional mesh generation (1989)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: An intense research effort over the last few years has produced several competing and apparently diverse methods for generating meshes. Recent progress is reviewed and the central themes are emphasized which form a solid foundation for future developments in mesh generation.
    Keywords: AERODYNAMICS
    Type: NASA, Langley Research Center, Transonic Symposium: Theory, Application, and Experiment, Volume 1, Part 1; p 341-376
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  • 3
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    A procedure based on the Euler equations for correcting transonic wind tunnel wall interference (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Based on an optimization formulation, a procedure has been developed to evaluate Mach number and angle-of-attack corrections. The Euler equations are assumed to be the flow governing equations. To obtain efficient solutions for the optimization problem, the iterative solutions for the flow variables and the design parameters are simultaneously updated. In addition to the model lift and geometry, the procedure requires pressure measurements near the tunnel walls. The accuracy and efficiency of several optimization techniques are investigated. The effect of perturbing certain test conditions on the residual interference is investigated.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 88-0141
    Format: text
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  • 4
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    Three-dimensional nearfield characterization of a VSTOL jet in turbulent crossflow (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper documents the measurement and prediction of the near-field evolution of the steady, subsonic, turbulent three-dimensional external aerodynamic flow-field associated with a high speed jet issued from an orifice perpendicular to an imposed crossflow velocity field. A parabolic Navier-Stokes CFD solver is employed, utilizing a Kappa-epsilon closure system with algebraic Reynolds stress equation, in concert with suitably defined porous far-field boundary conditions and a virtual source initial condition procedure. The CFD results correlate well with NASA generated near-field LDA experimental data on mean velocity and rms fluctuation velocity (interpolated to turbulent kinetic energy) distributions. The numerical results in the farther field predict the vortex roll-up and jet deflection/entrainment characterization verified by pitot-static mean velocity experimental data. Detailed results are presented for a circular jet for velocity ratios ranging 4 to 8.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 87-0051
    Format: text
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  • 5
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    Multigrid solution of the Euler equations for aircraft configurations (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A multigrid scheme for solving the Euler equations is presented. The method has been successfully applied to two-dimensional airfoil calculations on both O-type and C-type meshes. In three dimensions the scheme has proved equally effective and calclations of flows over wing/body combinations are possible with convergence achieved in less than 100 cycles.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 84-0093
    Format: text
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  • 6
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    An interaction algorithm for three-dimensional turbulent subsonic aerodynamic juncture region flow (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: (Previously cited in issue 06, p. 796, Accession no. A82-17782)
    Keywords: AERODYNAMICS
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  • 7
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    An interaction algorithm for prediction of mean and fluctuating velocities in two-dimensional aerodynamic wake flows (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A theoretical analysis is presented yielding sets of partial differential equations for determination of turbulent aerodynamic flowfields in the vicinity of an airfoil trailing edge. A four phase interaction algorithm is derived to complete the analysis. Following input, the first computational phase is an elementary viscous corrected two dimensional potential flow solution yielding an estimate of the inviscid-flow induced pressure distribution. Phase C involves solution of the turbulent two dimensional boundary layer equations over the trailing edge, with transition to a two dimensional parabolic Navier-Stokes equation system describing the near-wake merging of the upper and lower surface boundary layers. An iteration provides refinement of the potential flow induced pressure coupling to the viscous flow solutions. The final phase is a complete two dimensional Navier-Stokes analysis of the wake flow in the vicinity of a blunt-bases airfoil. A finite element numerical algorithm is presented which is applicable to solution of all partial differential equation sets of inviscid-viscous aerodynamic interaction algorithm. Numerical results are discussed.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3301 , COMCO-80-TR-1.0
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  • 8
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    An implicit and stiffly stable finite element CFD algorithm for unsteady aerodynamics (1989)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A stable and accurate finite element CFD algorithm for hyperbolic/incompletely parabolic conservation law systems is described and verified. It combines a Taylor weak statement FEM, an optimal implicit Runge-Kutta time integration algorithm, and a matrix tensor product approximate factorization linear algebra procedure. The results of computational experiments show that the developed algorithm is robust.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-0656
    Format: text
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  • 9
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    Progress on a Taylor weak statement finite element algorithm for high-speed aerodynamic flows (1989)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A new finite element numerical Computational Fluid Dynamics (CFD) algorithm has matured to the point of efficiently solving two-dimensional high speed real-gas compressible flow problems in generalized coordinates on modern vector computer systems. The algorithm employs a Taylor Weak Statement classical Galerkin formulation, a variably implicit Newton iteration, and a tensor matrix product factorization of the linear algebra Jacobian under a generalized coordinate transformation. Allowing for a general two-dimensional conservation law system, the algorithm has been exercised on the Euler and laminar forms of the Navier-Stokes equations. Real-gas fluid properties are admitted, and numerical results verify solution accuracy, efficiency, and stability over a range of test problem parameters.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-0654
    Format: text
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  • 10
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    Improvements to the aircraft Euler method (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An unstructured mesh of tetrahedra offers an attractive approach to mesh generation for complex three dimensional shapes. The combination of a method for constructing tetrahedral meshes and a finite element technique for solving the Euler equations has resulted in a powerful new approach to the problem of calculating flows over complex geometries. Recent progress and improvements to the authors' aircraft Euler method are described and results presented to demonstrate its capability.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 87-0452
    Format: text
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