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  • 1
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    Vortex simulation of forced/unforced mixing layers (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 25; 1417
    Format: text
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  • 2
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    A theory for turbulent curved wall jets (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An attempt is made to formulate the simplest possible model for the flow of a wall jet emanating from a two dimensional source into quiescent surroundings in the presence of a wall of arbitrary shape. The method used self similar profiles for the mean velocity together with a simple eddy viscosity model. The streamwise and radial momentum equations are integrated across the wall jet flow to give an expression for the momentum balance including the effect of the pressure gradient induced by the rate of change of surface curvature. The streamwise momentum equation is also evaluated at the point of maximum velocity to provide a second equation and thereby permit a solution for the two unknown quantities, the jet half width and the maximum velocity. This approach provides approximate closed form solutions for the flow of the wall jet over surfaces of various shapes, and in particular permits a direct comparison with the available experimental results for plane, cylindrical or logarithmic spiral surfaces.
    Keywords: AERODYNAMICS
    Type: NASA. Ames Research Center Proceedings of the Circulation-Control Workshop, 1986; p 99-112
    Format: application/pdf
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  • 3
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    Vortex simulation of forced mixing layers (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Two-dimensional, spatially growing, turbulent mixing layers are simulated numerically by a vortex method and the results are compared with those determined experimentally. The effects of artificial forcing on flow development are also studied. Many of the flow features which have been observed experimentally are reproduced, and good quantitative agreements between experiments and computations are obtained.
    Keywords: AERODYNAMICS
    Type: NASA-TM-88235 , A-86191 , NAS 1.15:88235
    Format: application/pdf
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  • 4
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    Control of vortical separation on conical bodies (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: In a variety of aeronautical applications, the flow around conical bodies at incidence is of interest. Such applications include, but are not limited to, highly maneuverable aircraft with delta wings, the aerospace plane and nose portions of spike inlets. The theoretical model used has three parts. First, the single line vortex model is used within the framework of slender body theory, to compute the outer inviscid field for specified separation lines. Next, the three dimensional boundary layer is represented by a momentum equation for the cross flow, analogous to that for a plane boundary layer; a von Karman Pohlhausen approximation is applied to solve this equation. The cross flow separation for both laminar and turbulent layers is determined by matching the pressure at the upper and lower separation points. This iterative procedure yields a unique solution for the separation lines and consequently for the position of the vortices and the vortex lift on the body. Lastly, control of separation is achieved by blowing tangentially from a slot located along a cone generator. It is found that for very small blowing coefficients, the separation can be postponed or suppressedy completely.
    Keywords: AERODYNAMICS
    Type: NASA-CR-181206 , NAS 1.26:181206 , JIAA-TR-78
    Format: application/pdf
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  • 5
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    Control of separated flow past a cylinder using tangential wall jet blowing (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A theoretical analysis is conducted to study the effect of a tangential wall jet on the control of two dimensional separated flow past a circular cylinder. For a tangential wall jet, the mathematical model derived previously is used and the vortex cloud method is adopted for the calculation of the external flow field. For certain limiting cases, the governing equations are simplified and closed forms of solutions for the wall jet parameters can be obtained. It is observed that the wall jet is very efficient in reducing drag by delaying the separation point in the range of small blowing strength. The suction force induced by the wall jet is negligible to the drag due to the external stream. However this suction increases the drag when the blowing strength is large.
    Keywords: AERODYNAMICS
    Type: NASA-CR-185918 , NAS 1.26:185918 , JIAA-TR-93
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  • 6
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    Numerical study of delta wing leading edge blowing (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Spanwise and tangential leading edge blowing as a means of controlling the position and strength of the leading edge vortices are studied by numerical solution of the three-dimensional Navier-Stokes equations. The leading edge jet is simulated by defining a permeable boundary, corresponding to the jet slot, where suitable boundary conditions are implemented. Numerical results are shown to compare favorably with experimental measurements. It is found that the use of spanwise leading edge blowing at moderate angle of attack magnifies the size and strength of the leading edge vortices, and moves the vortex cores outboard and upward. The increase in lift primarily comes from the greater nonlinear vortex lift. However, spanwise blowing causes earlier vortex breakdown, thus decreasing the stall angle. The effects of tangential blowing at low to moderate angles of attack tend to reduce the pressure peaks associated with leading edge vortices and to increase the suction peak around the leading edge, so that the integrated value of the surface pressure remains about the same. Tangential leading edge blowing in post-stall conditions is shown to re-establish vortical flow and delay vortex bursting, thus increasing C sub L sub max and stall angle.
    Keywords: AERODYNAMICS
    Type: NASA-CR-183101 , NAS 1.26:183101 , JIAA-TR-86
    Format: application/pdf
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  • 7
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    Numerical study of the effect of tangential leading edge blowing on delta wing vortical flow (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A numerical simulation of tangential blowing along the leading edge of a delta wing is analyzed as a means of controlling the position and strength of the leading-edge vortices. The computation is done by numerical solutions of the three-dimensional thin-layer Navier-Stokes equations. Numerical results are shown to compare favorably with experimental measurements. It is found that the use of tangential leading-edge blowing at low to moderate angles of attack tends to reduce the pressure peaks associated with leading-edge vortices and to increase the suction peak around the leading edge, such that the integrated value of the surface pressure remains about the same.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-0341
    Format: text
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  • 8
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    Vortex simulation of forced/unforced mixing layers (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two-dimensional, spatially growing, turbulent mixing layers are simulated numerically by a vortex method and the results are compared with those determined experimentally. The effects of artificial forcing on flow development are also studied. Many of the flow features which have been observed experimentally are reproduced, and good quantitative agreements between experiments and computations are obtained.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 87-0288
    Format: text
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  • 9
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    Transpiration cooling in hypersonic flight (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A preliminary numerical study of transpiration cooling applied to a hypersonic configuration is presented. Air transpiration is applied to the NASA all-body configuration flying at an altitude of 30500 m with a Mach number of 10.3. It was found that the amount of heat disposal by convection is determined primarily by the local geometry of the aircraft for moderate rates of transpiration. This property implies that different areas of the aircraft where transpiration occurs interact weakly with each other. A methodology for quick assessments of the transpiration requirements for a given flight configuration is presented.
    Keywords: AERODYNAMICS
    Type: NASA-CR-186435 , NAS 1.26:186435 , SU-JIAA-TR-92
    Format: application/pdf
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  • 10
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    A CFD study of tilt rotor flowfields (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The download on the wing produced by the rotor wake of a tilt rotor vehicle in hover is of major concern because of its severe impact on payload-carrying capability. In a concerted effort to understand the fundamental fluid dynamics that cause this download, and to help find ways to reduce it, computational fluid dynamics (CFD) is employed to study this problem. The thin-layer Navier-Stokes equations are used to describe the flow, and an implicit, finite difference numerical algorithm is the method of solution. The methodology is developed to analyze the tilt rotor flowfield. Included are discussions of computations of an airfoil and wing in freestream flows at -90 degrees, a rotor alone, and wing/rotor interaction in two and three dimensions. Preliminary results demonstrate the feasibility and great potential of the present approach. Recommendations are made for both near-term and far-term improvements to the method.
    Keywords: AERODYNAMICS
    Type: NASA-CR-186116 , JIAA-TR-96 , NAS 1.26:186116
    Format: application/pdf
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