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  • 1
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    Improved finite-difference schemes for transonic potential flow calculations (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 25; 1456-146
    Format: text
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  • 2
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    Time-marching transonic flutter solutions including angle-of-attack effects (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2109, Accession no. A82-30152
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft (ISSN 0021-8669); 20; 899-906
    Format: text
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  • 3
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    Nonreflecting boundary conditions for the complete unsteady transonic small-disturbance equation (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Nonreflecting far-field boundary conditions that are consistent with the complete transonic small-disturbance (TSD) equations are derived. They are implemented in a new code for solving the complete TSD equation and are tested for a harmonically oscillating NACA 64A010 airfoil in transonic flow and for a flat-plate airfoil with a pulse in the angle of attack. Using the new boundary conditions on a relatively small grid, solutions for the airfoil that are obtained that agree with large-grid calculations, resulting in a 44 percent savings in computer time. Frequency responses for the flat plate show that most of the disturbances incident on the computational boundaries are absorbed by the boundary conditions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 23; 315-317
    Format: text
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  • 4
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    An entropy correction method for unsteady full potential flows with strong shocks (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An entropy correction method for the unsteady full potential equation is presented. The unsteady potential equation is modified to account for entropy jumps across shock waves. The conservative form of the modified equation is solved in generalized coordinates using an implicit, approximate factorization method. A flux-biasing differencing method, which generates the proper amounts of artificial viscosity in supersonic regions, is used to discretize the flow equations in space. Comparisons between the present method and solutions of the Euler equations and between the present method and experimental data are presented. The comparisons show that the present method more accurately models solutions of the Euler equations and experiment than does the isentropic potential formulation.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-1768
    Format: text
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  • 5
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    Unsteady transonic flows past airfoils using the Euler equations (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An explicit finite difference solver for the Euler equations was developed and used to calculate the flow past two of the AGARD standard aeroelastic configurations, an NACA 64A010 and an NLR 7301. The algorithm employed uses a modified four step Runge-Kutta time stepping scheme, boundary conditions determined from the time-dependent theory of characteristics and an unsteady automatic grid generation procedure. In general, the calculated results are in good agreement with available experiment. Moreover, they demonstrate the importance of using the Euler equations for super-critical airfoils and in situations where the transonic small disturbance theory results in poor agreement with experiment.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-1764
    Format: text
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  • 6
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    Nonisentropic unsteady three dimensional small disturbance potential theory (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Nonisentropic modifications to the three-dimensional transonic small disturbance (TSD) theory, which allows for more accurate modeling of transonic flow fields, are described. The modified flux equation and entropy corrections are presented; the Engquist-Osher differencing (1980) is added to the solution algorithm in order to eliminate the velocity overshoots upstream of shocks. The modified theory is tested in the XTRAN3S finite difference computer code. Steady flows over a rectangular NACA 0012 wing with an aspect ratio of 12 are calculated and compared to Euler equation solutions; good correlation is observed between the data and the modified TSD theory provides more accurate data, particularly for the lift curve slope. The nonisentropic theory is evaluated on an RAE tailplane model for steady and unsteady flows and the modified theory results agree well with the experimental data.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-0863
    Format: text
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  • 7
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    An entropy correction method for unsteady full potential flows with strong shocks (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An entropy correction method for the unsteady full potential equation is presented. The unsteady potential equation is modified to account for entropy jumps across shock waves. The conservative form of the modified equation is solved in generalized coordinates using an implicit, approximate factorization method. A flux-biasing differencing method, which generates the proper amounts of artificial viscosity in supersonic regions, is used to discretize the flow equations in space. Comparisons between the present method and solutions of the Euler equations and between the present method and experimental data are presented. The comparisons show that the present method more accurately models solutions of the Euler equations and experiment than does the isentropic potential formulation.
    Keywords: AERODYNAMICS
    Type: NASA-TM-87769 , NAS 1.15:87769
    Format: application/pdf
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  • 8
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    Entropy condition satisfying approximations for the full potential equations of transonic flow (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A class of conservative difference approximations for the steady full potential equation was presented. They are, in general, easier to program than the usual density biasing algorithms, and in fact, differ only slightly from them. Rigorous proof indicated that these new schemes satisfied a new discrete entropy inequality, which ruled out expansion shocks, and that they have sharp, steady, discrete shocks. A key tool in the analysis is the construction of a new entropy inequality for the full potential equation itself. Results of some numerical experiments using the new schemes are presented.
    Keywords: AERODYNAMICS
    Type: NASA-TM-85751 , NAS 1.15:85751
    Format: application/pdf
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  • 9
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    XTRAN2L: A program for solving the general-frequency unsteady transonic small disturbance equation (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A program, XTRAN2L, for solving the general-frequency unsteady transonic small disturbance potential equation was developed. It is a modification of the LTRAN2-NLR code. The alternating-direction-implicit (ADI) method of Rizzetta and Chin is used to advance solutions of the potential equation in time Engquist-Osher monotone spatial differencing is used in the ADI solution algorithm. As a result, the XTRAN2L code is more robust and more efficient than similar codes that use Murman-Cole type-dependent spatial differencing. Nonreflecting boundary conditions that are consistent with the general-frequency equation have been developed and implemented at the far-field boundaries. Use of those conditions allow the computational boundaries to be moved closer to the airfoil with no loss of accuracy. This makes the XTRAN2L code more economical to use.
    Keywords: AERODYNAMICS
    Type: NASA-TM-85723 , NAS 1.15:85723
    Format: application/pdf
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  • 10
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    Characteristic boundary conditions for three-dimensional transonic unsteady aerodynamics (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Characteristic far-field boundary conditions for the three-dimensional unsteady transonic small disturbance potential equation have been developed. The boundary conditions were implemented in the XTRAN3S finite difference code and tested for a flat plate rectangular wing with a pulse in angle of attack; the freestream Mach number was 0.85. The calculated force response shows that the characteristic boundary conditions reduce disturbances that are reflected from the computational boundaries.
    Keywords: AERODYNAMICS
    Type: NASA-TM-86292 , NAS 1.15:86292
    Format: application/pdf
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