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  • 1
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    Effect of boundary layers on solid walls in three-dimensional subsonic wind tunnels (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: A solution for the tunnel wall boundary layer effects for three-dimensional subsonic tunnels is presented. The model potentials are represented with simple singularities placed on the centerline of the tunnel and Laplace's equation in cylindrical coordinates is solved for either the conventional homogeneous slotted-wall boundary condition, the solid-wall viscous boundary condition, or a combination of them. The most pronounced wall boundary layer effect is on solid blockage for completely closed wind tunnels. Boundary layers on the wall reduce the blockage from the solid-wall, no-boundary-layer case in a manner similar to opening slots in a solid wall. Additionally, for solid-wall tunnel configurations, the streamline curvature interference factor is reduced by a significant amount, whereas the lift interference factor at the model station does not depend on the boundary layer parameter. For combination wall configurations, the slot effect of the horizontal walls dominates the viscous effect of the solid sidewalls.
    Keywords: AERODYNAMICS
    Type: Wind Tunnel Wall Interference Assessment and Correction, 1983; p 205-218
    Format: text
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  • 2
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    Transonic-flow computation using an explicit-implicit method (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The explicit-implicit predictor corrector method of MacCormack (1981) is applied to the analysis of flows past airfoils. By comparing results obtained with different methods and meshes, it is shown that the above method provides, after certain modifications, reasonably good predictions of inviscid and viscous flows about an airfoil. Good results are also obtained for the transonic regime if the free-stream conditions are correct and if a suitable mesh is used.
    Keywords: AERODYNAMICS
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  • 3
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    Effect of boundary layers on solid walls in three-dimensional subsonic wind tunnels (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Previously cited in issue 05, p. 580, Accession no. A83-16553
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 22; 365-371
    Format: text
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  • 4
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    Effect of sidewall suction on flow in two-dimensional wind tunnels (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A closed-form analysis of flow in a two-dimensional subsonic wind tunnel which uses sidewall suction around the model to reduce sidewall boundary-layer effects is presented. The model problem which is treated involves a flat plate airfoil in a tunnel with a suction window shaped to permit an analytic solution. This solution shows that the lift coefficient depends explicitly on the porosity parameter of the suction window and implicitly on the suction pressure differential. For a given sidewall displacement thickness, the lift coefficient increases as the suction-window porosity decreases.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 84-0242
    Format: text
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  • 5
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    Viscous shock-layer flowfield analysis by an explicit-implicit method (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The present work extends the recently reported implicit analogue of MacCormack's earlier widely-used explicit method to external axisymmetric laminar flows with strong entropy gradients. The details of the 'numerics' of the implicit part are provided in a body-oriented coordinate system with a moving outer (shock) boundary during the transient part of the solutions. The limiting values of the Courant number are obtained when the shock boundary is treated explicitly. The solution algorithm outlined includes the treatment of the source term associated with the equations in weak conservation form. From the results obtained for two sample problems, it becomes clear that accuracy of predictions is, indeed, very good at higher values of the Courant number. There is a significant saving in overall computing time, depending on the Courant number used and the flow Reynolds number. These properties combined with the simplicity of programming the implicit analogue may appeal to researchers for using it in the analysis of three-dimensional flow problems.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 83-1423
    Format: text
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  • 6
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    Numerical solution of compressible viscous flows at high Reynolds numbers (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new numerical method which was used to reduce the computation time required in fluid dynamics to solve the Navier-Stokes equations at flight Reynolds numbers is described. The method is the implicit analogue of the explicit finite different method. It uses this as its first stage, while the second stage removes the restrictive stability condition by recasting the difference equations in an implicit form. The resulting matrix equations to be solved are either upper or lower block bidiagonal equations. The new method makes it possible and practical to calculate many important three dimensional, high Reynolds number flow fields on computers.
    Keywords: AERODYNAMICS
    Type: NASA-TM-81279 , A-8524
    Format: application/pdf
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  • 7
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    Jet decay rate effects on hover jet-induced loads (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The paper explains the mechanisms for observed jet decay rate effects on jet-induced loads on a flat plate for cross-flow and hover configurations. Examples are presented for the influence of the decay rate on integrated loads on a flat plate induced by the jet issuing at a right angle from the plate into still air; knowledge of these jet-induced loadings is of particular importance for VTOL aircraft design because they produce an effective loss in the lift force available in hover. The apparent inconsistency between existing lift loss vs jet decay rate trends is explained in light of the different mechanism which determine the jet mixing and trajectory, i.e., entrainment, blockage, and the vortex pair associated with a jet in crossflow.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft; 17; Aug. 198
    Format: text
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  • 8
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    New approach to the solution of large, full matrix equations (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A new approach to the solution of matrix equations resulting from integral equations is presented and applied to the solution of two-dimensional Neumann problems describing the inviscid, incompressible flow past an airfoil. The problem is reformulated in terms of a preselected set of mode functions giving an equivalent matrix equation to be solved for the mode-function expansion coefficients. Because of the inherent smoothness of the original problem, the coefficient problem can be solved approximately without significantly affecting the accuracy of the final solution. Very promising two-dimensional results are obtained and the extension of the method to three-dimensional problems is investigated. On the basis of these results it is shown that the computing time for the matrix solution for a large three-dimensional panel method calculation could be reduced by an order of magnitude compared with that required for a direct solution.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 19; Feb. 198
    Format: text
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  • 9
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    A potential-flow/boundary-layer method for calculating subsonic and transonic airfoil flow with trailing-edge separation (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The development of a potential-flow/boundary-layer method for calculating subsonic and transonic turbulent flow past airfoils with trailing-edge separation is reported. A moment-of-momentum integral boundary-layer method is used which employs the law-of-the-wall/law-of-the-wake velocity profile and a two-layer eddy-viscosity model and ignores the laminar sublayer. All integrals across the boundary layer are obtained in closed form. Separation is assumed to occur when the shearing-stress velocity vanishes. A closed-form solution is derived for separated-flow regions where the shearing stress is negligible. In the potential-flow method, the exact form of the airfoil boundary condition is used, but it is applied at the chord line rather than the airfoil surface. This allows the accurate computation of flow about airfoils at large angles of attack but permits the use of body-oriented Cartesian computational grids. The governing equation for the perturbation velocity potential contains several terms in addition to the classical small-disturbance terms.
    Keywords: AERODYNAMICS
    Type: NASA-TM-81850 , L-14255
    Format: application/pdf
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  • 10
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    Low speed performance of a supersonic axisymmetric mixed compression inlet with auxiliary inlets (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The aerodynamic performance of a representative supersonic cruise inlet was investigated using a fan simulator coupled to the inlet to provide characteristic noise signatures and to pump the inlet flow. Data were obtained at Mach numbers from 0 to 0.2 for the inlet equipped with an auxiliary inlet system that provided 20 to 40 percent of the fan flow. Results show that inlet performance improved when the inlet bleed systems were sealed; when the freestream Mach number was increased; and when the auxiliary inlets were opened. The inlet flow could not be choked by either centerbody translation or by increasing the fan speed when the 40 percent auxiliary inlet was incorporated. Previously announced in STAR as N83-27992
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 83-1414
    Format: text
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