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  • 1
    Publication Date: 2018-12-01
    Description: Recent progress in the development of implicit algorithms for the Euler equations using the flux-vector splitting method is described. Comparisons of the relative efficiency of relaxation and spatially-split approximately factored methods on a vector processor for two-dimensional flows are made. For transonic flows, the higher convergence rate per iteration of the Gauss-Seidel relaxation algorithms, which are only partially vectorizable, is amply compensated for by the faster computational rate per iteration of the approximately factored algorithm. For supersonic flows, the fully-upwind line-relaxation method is more efficient since the numerical domain of dependence is more closely matched to the physical domain of dependence. A hybrid three-dimensional algorithm using relaxation in one coordinate direction and approximate factorization in the cross-flow plane is developed and applied to a forebody shape at supersonic speeds and a swept, tapered wing at transonic speeds.
    Keywords: NUMERICAL ANALYSIS
    Type: AIAA PAPER 85-1680
    Format: text
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  • 2
    Publication Date: 2018-12-01
    Description: A comparison is made between the computational results of the Steger-Warming (1981) and van Leer (1982) flux splitting methods, which have been applied in generalized coordinates to quasi-one-dimensional transonic flow in a nozzle and two-dimensional subsonic, transonic, and supersonic flow over airfoils. The latter splitting method leads to higher convergence rates and a sharper representation of shocks in the transition region. The second-order accurate, one-sided-difference model is extended to a third-order, upwind-biased model with only small additional computational effort.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-0122
    Format: text
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  • 3
    Publication Date: 2013-08-31
    Description: A description of and results from a solution algorithm for the compressible Navier-Stokes equations are presented. The main features of the algorithm are second or third order accurate upwind discretization of the convection and pressure derivatives and a relaxation scheme for the unfactored implicit backward Euler time method, implemented in a finite-volume formulation. Upwind methods were successfully used to obtain solutions to the Euler equations for flows with strong shock waves. The particular upwind method being used is based on the flux vector splitting technique developed by Van Leer and both second and third order accurate discretizations were developed. Currently, the most widely used implicit solution technique for the Navier-Stokes equations use approximate factorization (AF) methods to treat multidimensional problems. The time integration scheme being used in the present algorithm corresponds to a line Gauss-Seidel relaxation method. This method produces good convergence rates for steady-state flows, and most of the algorithm was vectorized on the NASA Langley VPS 32 computer. The Navier-Stokes algorithm was tested for several two-dimensional flow problems. Solutions for the problems gave excellent results. The presented effort is directed toward the extension of the scheme to the full three-dimensional Navier-Stokes equations.
    Keywords: AERODYNAMICS
    Type: Langley Symposium on Aerodynamics, Volume 1; p 89-107
    Format: application/pdf
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  • 4
    Publication Date: 2013-08-31
    Description: A brief overview of flow separation phenomena is provided. Langley has many active research programs in flow separation related areas. Three cases are presented which describe specific examples of flow separation research. In each example, a description of the fundamental fluid physics and the complexity of the flow field is presented along with a method of either reducing or controlling the extent of separation. The following examples are discussed: flow over a smooth surface with an adverse pressure gradient; flow over a surface with a geometric discontinuity; and flow with shock-boundary layer interactions. These results will show that improvements are being made in the understanding of flow separation and its control.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Langley Symposium on Aerodynamics, Volume 1; p 361-374
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  • 5
    Publication Date: 2013-08-31
    Description: Computational methods for unsteady transonic flows are surveyed with emphasis on prediction. Computational difficulty is discussed with respect to type of unsteady flow; attached, mixed (attached/separated) and separated. Significant early computations of shock motions, aileron buzz and periodic oscillations are discussed. The maturation of computational methods towards the capability of treating complete vehicles with reasonable computational resources is noted and a survey of recent comparisons with experimental results is compiled. The importance of mixed attached and separated flow modeling for aeroelastic analysis is discussed, and recent calculations of periodic aerodynamic oscillations for an 18 percent thick circular arc airfoil are given.
    Keywords: AERODYNAMICS
    Type: NASA-TM-89106 , AIAA PAPER 87-0107 , NAS 1.15:89106
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  • 6
    Publication Date: 2013-08-31
    Description: An efficient finite-difference scheme for the solution of the incompressible Navier-Stokes equation is used to study the vortex wake of a rotor in hover. The solution Procedure uses a vorticity-stream function formulation and incorporates an asymptotic far-field boundary condition enabling the size of the computational domain to be reduced in comparison to other methods. The results from the present method are compared with experimental data obtained by smoke flow visualization and hot-wire measurements for several rotor blade configurations.
    Keywords: AERODYNAMICS
    Type: A-9611 , NASA-TM-85894 , NAS 1.15:85894 , USAAVSCOM-TR-84-A-3
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  • 7
    Publication Date: 2013-08-31
    Description: Transonic viscous-inviscid interaction is considered using the Euler and inverse compressible turbulent boundary-layer equations. Certain improvements in the inverse boundary-layer method are mentioned, along with experiences in using various Runge-Kutta schemes to solve the Euler equations. Numerical conditions imposed on the Euler equations at a surface for viscous-inviscid interaction using the method of equivalent sources are developed, and numerical solutions are presented and compared with experimental data to illustrate essential points.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NAS 1.15:85203 , NASA-TM-85203
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  • 8
    Publication Date: 2013-08-31
    Description: An investigation was conducted in the Langley V/STOL tunnel to determine the effect of longitudinally oriented wing-mounted pods on the longitudinal and lateral aerodynamic characteristics in the cruise flight condition of a high-wing V/STOL transport model. Five pod arrangements were tested - three configurations with in-line pods at 20, 40, or 60 percent semispan and two split pod configurations with rear pods at 20 percent semispan and front pods at 40 or 60 percent semispan. In general, addition of the pods to the model decreased the stability, increased the lift-curve slope, and alleviated the abrupt stall of the basic model. The configuration with pods at 20 percent semispan had an abrupt instability at 10 deg angle of attack, All the configurations had lateral stability at sideslip angles from 5 to -5 deg. Very little difference in results existed between the configurations with pods at 40 and 60 percent semispan. Of the split pod configurations, the configuration with front pods at 40 percent semispan offered the best trimmed lift and lift-induced drag characteristics at high angles of attack. The configuration with in-line pods at 40 or 60 percent semispan provided the best cruise characteristics of all the pod configurations.
    Keywords: AERODYNAMICS
    Type: NASA-TN-D-7199 , L-8754
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  • 9
    Publication Date: 2013-08-31
    Description: Investigations of the low speed longitudinal characteristics of two powered close coupled wing-canard fighter configurations are discussed. Data obtained at angles of attack from -2 deg to 42 deg, Mach numbers from 0.12 to 0.20, nozzle and flap deflections from 0 deg to 40 deg, and thrust coefficients from 0 to 2.0, to represent both high angle of attack subsonic maneuvering characteristics and conventional takeoff and landing characteristics are examined. Data obtained with the nozzles deflected either 60 deg or 90 deg and the flaps deflected 60 deg to represent vertical or short takeoff and landing characteristics are discussed.
    Keywords: AERODYNAMICS
    Type: L-13157 , NASA-TP-1535
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  • 10
    Publication Date: 2013-08-31
    Description: A series of wind-tunnel tests were conducted in a V/STOL tunnel to determine the low-speed longitudinal aerodynamic characteristics of a powered close-coupled wing/canard fighter configuration. The data was obtained for a high angle-of-attack maneuvering configuration and a takeoff and landing configuration. The data presented in tabulated form are intended for reference purposes.
    Keywords: AERODYNAMICS
    Type: NASA-TM-78722
    Format: application/pdf
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