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  • 11
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    A fast viscous correction method for full-potential transonic wing analysis (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: An analysis of the transonic flowfield around a three-dimensional wing is carried out using a strip method. Attention is given to the boundary layer growth in the streamwise direction. A viscous correction technique is defined for the TWING code for solving the full potential equations. A viscous ramp at the base of a shock is superimposed on the boundary layer displacement thickness generated by an integral boundary layer method. A relationship is then obtained between the effective displacement thickness and a vertical component of the surface velocity, a transpirational boundary condition. The viscous correction is found to be unnecessary in weak shock conditions but gives a better shock position and pressure distribution in a strong shock condition when compared with data from an ONERA M6 airfoil and the Hinson and Burdges (1980) Wing A.
    Keywords: AERODYNAMICS
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  • 12
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    The relative merits of several numerical techniques for solving the compressible Navier-Stokes equations (1976)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Four explicit finite difference techniques designed to solve the time-dependent, compressible Navier Stokes equations are compared. These techniques are: (1) MacCormack, (2) modified Du Fort-Frankel, (3) modified hopscotch, and (4) Brailovskaya. The comparison was made numerically by solving the quasi-one dimensional Navier Stokes equations for the flow in a converging-diverging nozzle. Solutions with and without standing normal shock waves were computed for unit Reynolds numbers (based on total conditions) ranging from 45374 to 2269. The results indicate that all four techniques are comparable in accuracy; however, the modified hopscotch scheme is two to three times faster than the Brailovskaya and MacCormack schemes and three to six times faster than the modified Du Fort-Frankel scheme.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Advan. in Eng. Sci., Vol. 4; p 1467-1481
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  • 13
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    Numerical simulation of transonic separated flows over low-aspect ratio wings (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Transonic flow fields about a low-aspect-ratio advanced technology wing have been computed using a viscous/inviscid zonal approach. The flow field near the wing where viscous effects are important was solved using the 'Reynolds-Averaged Navier-Stokes Equations' in 'thin-layer' form. The Euler equations were used to determine the flow field in regions away from the wing where viscous effects are insignificant. A zonal grid using an H-H topology was generated around the wing by first solving a set of Poisson's equations for the global grid. This grid was then subdivided into separate zones of viscous or inviscid flow as suggested by the flow physics. A series of flow cases were computed and compared with corresponding sets of experimental data. All cases showed good agreement with experiment in terms of the pressure field. Also, a good correlation between computed separated surface flow and experimental oil flow was obtained.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-0508
    Format: text
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  • 14
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    Numerical simulation of transonic flow over porous airfoils (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A numerical study was made to examine the effect of a porous surface on the aerodynamic performance of a transonic airfoil. The pressure jump across the normal shock wave on the upper surface of the airfoil was reduced by making the surface below the shock porous. The weakened shock is preceded by an oblique shock at the upstream end of the porous surface where air is blown out of the cavity. The lambda shock structure shown in the numerical result qualitatively agrees with that observed in the wind tunnel. According to the present analysis, the porous airfoil has a smaller drag and a higher lift than the solid airfoil.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-5022
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  • 15
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    A consistent spatial differencing scheme for the transonic full-potential equation in three dimensions (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A full-potential steady transonic wing flow solver has been modified so that freestream density and residual are captured in regions of constant velocity. This numerically precise freestream consistency is obtained by slightly altering the differencing scheme without affecting the implicit solution algorithm. The changes chiefly affect the fifteen metrics per grid point, which are computed once and stored. With this new method, the outer boundary condition is captured accurately, and the smoothness of the solution is especially improved near regions of grid discontinuity.
    Keywords: AERODYNAMICS
    Type: NASA-TM-86716 , REPT-85213 , NAS 1.15:86716
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  • 16
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    Computational aspects of zonal algorithms for solving the compressible Navier-Stokes equations in three dimensions (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Transonic flow fields about wing geometries are computed using an Euler/Navier-Stokes approach in which the flow field is divided into several zones. The flow field immediately adjacent to the wing surface is resolved with fine grid zones and solved using a Navier-Stokes algorithm. Flow field regions removed from the wing are resolved with less finely clustered grid zones and are solved with an Euler algorithm. Computational issues associated with this zonal approach, including data base management aspects, are discussed. Solutions are obtained that are in good agreement with experiment, including cases with significant wind tunnel wall effects. Additional cases with significant shock induced separation on the upper wing surface are also presented.
    Keywords: AERODYNAMICS
    Type: NASA-TM-86774 , REPT-85340 , NAS 1.15:86774
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  • 17
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    Evaluation of Navier-Stokes and Euler solutions for leading-edge separation vortices (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Extensive study on the numerical simulation of the vortical flow over a double delta wing is carried out using the thin layer Navier-Stokes and Euler equations. Two important flow characteristics, vortex interaction and vortex breakdown, are successfully simulated. Grid resolution is one of the most important factors associated with the vortex problem. Computations were performed on a series of grids with various levels of refinement, coarse, medium, and fine. Computations using either the coarse or medium grids fail to capture the proper physical phenomena. The computed result using a fine grid shows flow unsteadiness once the vortex breakdown takes place. The C sub L - alpha characteristics are well predicted up to the breakdown angle of attack for all the grid distributions. The Euler solutions show fairly good agreement with the experiment on the C sub L - alpha characteristics. However, other aspects of the solution at each angle of attack, such as the locus of the leading edge separation vortex, are not consistent with the experiment. Even for the fine grid Navier-Stokes computations, further grid resolution is required to obtain good quantitative agreement with the experiment.
    Keywords: AERODYNAMICS
    Type: NASA-TM-89458 , A-87202 , NAS 1.15:89458
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  • 18
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    Numerical solution of transonic wing flows using an Euler/Navier-Stokes zonal approach (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Transonic flow fields about wing geometries are computed using an Euler/Navier-Stokes approach in which the flow field is divided into several zones. The grid zones immediately adjacent to the wing surface are suitably clustered and solved with the Navier-Stokes equations. Grid zones removed from the wing are less finely clustered and are solved with the Euler equations. Wind tunnel wall effects are easily and accurately modeled with the new grid-zoning algorithm because the wind tunnel grid is constructed as an exact subset of the corresponding free-air grid. Solutions are obtained that are in good agreement with experiment, including cases with significant wind tunnel wall effects and shock-induced separation on the upper wing surface.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-1640
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  • 19
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    Numerical study of porous airfoils in transonic flow (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A numerical study was made to examine the effect of a porous surface on the aerodynamic performance of a transonic airfoil. The pressure jump across the normal shock wave on the upper surface of the airfoil was reduced by making the surface below the shock porous. The weakened shock is preceded by an oblique shock at the upstream end of the porous surface where air is blown out of the cavity. The lambda shock structure shown in the numerical result qualitatively agrees with that observed in the wind tunnel. According to the present analysis, the porous airfoil has a smaller drag and a higher lift than the solid airfoil.
    Keywords: AERODYNAMICS
    Type: NASA-TM-86713 , REPT-85209 , NAS 1.15:86713
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  • 20
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    Comparison of the full potential and Euler formulations for computing transonic airfoil flows (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A quantitative comparison between the Euler and full potential formulations with respect to speed and accuracy is presented. The robustness of the codes used is tested by a number of transonic airfoil cases. The computed results are from four transonic airfoil computer codes. The full potential codes use fully implicit iteration algorithms. The first Euler code uses a fully implicit ADI iteration scheme. The second Euler code uses an explicit Runge Kutta time stepping algorithm which is enhanced by a multigrid convergence acceleration scheme. Quantitative comparisons are made using various plots of lift coefficient versus the average mesh spacing along the airfoil. Besides yielding an asymptotic limit to the lift coefficient, these results also demonstrate the truncation error behavior of the various codes. Quantitative conclusions regarding the full potential and Euler formulations with respect to accuracy, speed, and robustness can be presented.
    Keywords: AERODYNAMICS
    Type: NASA-TM-85983 , A-9816 , NAS 1.15:85983
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