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  • 1
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    Publication Date: 2011-08-24
    Description: Jet noise and jet-induced structural loads have become key issues in the design of commercial and military aircraft. Computational Fluid Dynamics (CFD) can be of use in predicting the underlying jet shear-layer instabilities and, in conjunction with classical acoustic theory, jet noise. The computational issues involved in the resolution of high Reynolds number unsteady jet flows are addressed in this paper. Once these jet flows can be accurately resolved, it should be possible to use acoustic theory to extract, for example, the far-field jet noise. An assessment of future work and computational resources required for directly computing far-field jet noise is also presented.
    Keywords: AERODYNAMICS
    Type: Computing Systems in Engineering (ISSN 0956-0521); 3; 1-4; p. 169-179.
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  • 2
    Publication Date: 2019-07-27
    Description: The flow past a 60-deg delta wing equipped with two thrust-reverser jets near the inboard trailing edge has been analyzed by numerical solution of the 3D thin-layer Navier-Stokes equations. An implicit, partially flux-split, approximately-factored Navier-Stokes solver coupled with a multiple grid embedding scheme has been adapted to this problem. Studies of the impact of numerical parameters (e.g., grid refinement and dissipation levels), and flow-field parameters such as the height of the delta wing above the ground plane and the jet size on the solution, were performed. Results of these numerical studies indicate some challenges in the accurate resolution of complex 3D free shear layers and jets. Nevertheless, flow features such as jet deformation and ground vortex formation observed in experimental flow visualizations are captured. Further, comparisons with experimental data confirm the ability to simulate the loss of wing-borne lift, commonly referred to 'suckdown, as the delta planform flies at slow speeds in close proximity to the ground. Detailed analysis of the numerical results has also given additional insight into the structure of the ground vortex and the mechanisms of lift loss.
    Keywords: AERODYNAMICS
    Type: SAE PAPER 892283 , ; 15 p.|SAE, Aerospace Technology Conference and Exposition; Sept. 25-28, 1989; Anaheim, CA; United States
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  • 3
    Publication Date: 2019-07-12
    Description: Report describes some experiences in numerical simulation of compressible, viscous flows by finite-difference approximations of Navier-Stokes equations. Focuses upon viscous/inviscid-interaction approach, in which flow mathematically modeled with interacting zones, within each of which different model of viscous or inviscid flow applies. Reduces task of computation by taking advantage of simpler models and coarser grids in some of zones.
    Keywords: MECHANICS
    Type: ARC-12115 , NASA Tech Briefs (ISSN 0145-319X); 15; 4; P. 85
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  • 4
    Publication Date: 2019-07-13
    Description: One of the flows inherent in V/STOL operations, the jet in ground effect with a crossflow, is studied using the Fortified Navier-Stokes (FNS) scheme. Through comparison of the simulation results and the experimental data, and through the variation of the flow parameters (in the simulation) a number of interesting characteristics of the flow have been observed. For example, it appears that the forward penetration of the ground vortex is a strong inverse function of the level of mixing in the ground vortex. An effort has also been made to isolate issues which require additional work in order to improve the numerical simulation of the jet in ground effect flow. The FNS approach simplifies the simulation of a single jet in ground effect, but will be even more effective in applications to more complex topologies.
    Keywords: AERODYNAMICS
    Type: SAE PAPER 872344 , International Powered Lift Conference and Exposition; Dec 07, 1987 - Dec 10, 1987; Santa Clara, CA; United States
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  • 5
    Publication Date: 2019-07-13
    Description: Compressible viscous flow simulation using finite difference Navier-Stokes and viscous-inviscid interaction methods is described. Recent developments are reviewed that significantly improve the computational efficiency of approximately factored implicit Navier-Stokes algorithms. Compared to Navier-Stokes codes, modern viscous-inviscid interaction codes are more computationally efficient, but have restricted application and are more complicated to program. Therefore, less efficient but more general viscous-inviscid interaction methods are investigated that use forcing functions instead of boundary condition matching, and a simple, direct/inverse, three-dimensional, finite-difference, boundary layer code is presented.
    Keywords: AERODYNAMICS
    Type: Symposium on Numerical and Physical Aspects of Aerodynamic Flows; Jan 21, 1985 - Jan 24, 1985; Long Beach, CA
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  • 6
    Publication Date: 2019-07-13
    Description: A computer code has been developed that couples a fast transonic full-potential AF2 solver with both an efficient integral boundary-layer method and a viscous wedge approximation of the shock/boundary-layer interaction. The efficiency of the coupled analysis methods and the method of coupling has resulted in a uniquely efficient analysis tool. The airfoil geometry is modified by the displacement thickness before the shock and the displacement thickness plus the viscous wedge thickness after the shock by considering the viscous effects as an equivalent transpiration boundary condition. The flow about conventional and supercritical airfoils under moderately strong shock situations has been calculated. Comparisons with experimental data indicate that this viscous correction method has improved the accuracy of the full-potential analysis. Furthermore, the computer time required to obtain a converged solution has been reduced.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 81-1002 , Computational Fluid Dynamics Conference; Jun 22, 1981 - Jun 23, 1981; Palo Alto, CA
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  • 7
    Publication Date: 2019-06-28
    Description: The viscous transonic flow about a multielement airfoil (augmentor-wing) is simulated by coupling full-potential and direct/inverse differential boundary-layer algorithms. Solutions have been obtained for a variety of conditions and are in fair agreement with available experimental data. Typical results from this transonic augmentor-wing code (TAUG-V) require approximately three minutes of CRAY-XMP CPU time. Since this viscous transonic code accounts for most of the important flow physics, yet is still economical, it is a practical tool for the design aerodynamicist.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-5004
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  • 8
    Publication Date: 2019-06-28
    Description: A new, fast, direct-inverse, finite-difference boundary-layer code has been developed and coupled with a full-potential transonic airfoil analysis code via new inviscid-viscous interaction algorithms. The resulting code has been used to calculate transonic separated flows. The results are in good agreement with Navier-Stokes calculations and experimental data. Solutions are obtained in considerably less computer time than Navier-Stokes solutions of equal resolution. Because efficient inviscid and viscous algorithms are used, it is expected this code will also compare favorably with other codes of its type as they become available.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 83-1689
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  • 9
    Publication Date: 2019-07-13
    Description: The flow field about a delta wing equipped with thrust reverser jets in slow speed flight near the ground has been computed. Results include the prediction of the flow about the delta wing at four fixed heights above the ground, and a simulated landing, in which the delta wing descends towards the ground. Comparison of computed and experimental lift coefficients indicates that the simulations can capture at least the qualitative trends in lift-loss encountered by thrust-vectoring aircraft operating in ground effect.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 92-4254 , AIAA, Aircraft Design Systems Meeting; Aug 24, 1992 - Aug 26, 1992; Hilton Head Island, SC; United States|; 10 p.
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  • 10
    Publication Date: 2019-06-28
    Description: The three-dimensional, thin-layer Navier-Stokes equations on a body-conforming, overset, multiple-grid topology are solved in the present numerical simulations of the flow around a 60-deg delta-planform wing equipped with two thrust-reverser jets in ground-effect conditions. Such experimentally flow-visualized features as jet-deformation and ground vertex-formation are captured by these simulations; the loss of wing-borne lift due to the 'suck-down' phenomenon, which arises as the delta planform flies at low speeds in close proximity to the ground, is also well simulated.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 90-0299
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