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  • Other Sources  (15)
  • 1985-1989  (12)
  • 1980-1984  (3)
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  • 1
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    Acoustic propagation using computational fluid dynamics (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The propagation characteristics of several helicopter airfoil profiles have been investigated using the transonic small disturbance equation. A test case was performed to generate a moving shock that propagated off the airfoil. Various grids were then examined to determine their ability to accurately capture these propagating shock waves. Finally, the case of airfoil-vortex interactions was thoroughly studied over a wide range of Mach numbers and airfoil shapes with particular emphasis on the transonic regime; this results in a highly conplicated fluctuation of lift, drag, and pitching moment. The calculated acoustic intensity levels, along with the details of the computational flow field, provide new insights into the understanding of transonic airfoil-vortex interactions.
    Keywords: AERODYNAMICS
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  • 2
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    Unsteady interactions of transonic airfoils with gusts and concentrated vortices (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Unsteady interactions of strong concentrated vortices, distributed gusts, and sharp-edged gusts with stationary airfoils were analyzed in two-dimensional transonic flow. A simple and efficient method for introducing such vortical disturbances was implemented in numerical codes that range from inviscid, transonic small-disturbance to thin-layer Navier Stokes. The numerical results demonstrate the large distortions in the overall flow field and in the surface air loads that are produced by various vortical interactions. The results of the different codes are in excellent qualitative agreement, but, as might be expected, the transonic small-disturbance calculations are deficient in the important region near the leading edge.
    Keywords: AERODYNAMICS
    Type: AGARD Unsteady Aerodynamics-Fundamentals and Applications to Aircraft Dynamics; 13 p
    Format: text
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  • 3
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    Tip vortices of wings in subsonic and transonic flow: A numerical simulation (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Thin layer Navier-Stokes and Euler equations are numerically solved using a multi-block zonal approach to simulate the formation and roll up of tip vortices of wings in subsonic and transonic flows. Several wing planforms were considered to examine the influence of tip-cap shape, planform geometry and free stream Mach number on the formation process. A good definition of the formation and qualitative roll up of tip vortices was achieved.
    Keywords: AERODYNAMICS
    Type: NASA-TM-88334 , A-86415 , NAS 1.15:88334 , USAAVSCOM-TM-86-A-4 , AD-A172312
    Format: application/pdf
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  • 4
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    Numerical simulation of tip vortices of wings in subsonic and transonic flows (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A multi block zonal algorithm which solves the thin-layer Navier-Stokes and the Euler equations is used to numerically simulate the formation and roll-up of the tip vortex in both subsonic and transonic flows. Four test cases which used small and large aspect ratio wings have been considered to examine the influence of the tip-cap shape, the tip planform and the free-stream Mach number. It appears that both the tip-planform and the tip-cap shape have some influence on the formation of the tip vortex, but its subsequent roll-up seems to be more influenced by the tip-planform shape. In general, a good definition of the formation and the roll-up of the tip vortex has been observed for all the cases considered here. Comparions of the numerical results with the limited, available experimental data show good agreement with both the surface pressures and the tip-vortex strength.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-1095
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  • 5
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    Unsteady interaction of a rotor with a vortex (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The unsteady, three-dimensional flow field of a helicopter rotor blade encountering a passing vortex is calculated by solving the Euler/thin layer Navier-Stokes equations by a finite-difference numerical procedure. A prescribed vortex method is adopted to preserve the structure of the interacting vortex. The cases considered for computation correspond to the experimental model rotor test conditions of Caradonna, et al. and consist of parallel and oblique interactions. Comparison of the numerical results with test data show good agreement for both parallel and oblique interactions at subsonic and transonic tip speeds.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-1848
    Format: text
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  • 6
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    Computations of two-dimensional airfoil-vortex interactions (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A procedure for calculating the interaction of a vortex with a two dimensional airfoil in a uniform free stream is presented along with results for several test cases. A Lamb like anaytical vortex having a finite core and convect in a uniform free stream interacts with the flowfield of NACA 0012 or NACA 64A006 airfoil in transonic and subsonic flow. Euler and thin layer Navier-Stokes solutions are computed and the results are compared with the results from transonic small disturbance code and available experimental results. For interactions within the limits of transonic small disturbance assumptions, the three methods gave qualitatively similar results of a two bladed helicopter rotor and suggest that the time lag effects of the free stream velocity approaching the blade may be important and should be considered in the analysis. In general, the results show a tremendous influence of the interacting vortex on the flowfield around the airfoil. This is particularly true when the vortex is stationary. For a convecting vortex, the most dramatic changes in the flowfield seem to occur when the vortex is within one chord of the airfoil.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3885 , NAS 1.26:3885 , FSI-84-01
    Format: application/pdf
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  • 7
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    Numerical simulation of the interaction of a vortex with stationary airfoil in transonic flow (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A perturbation form of an implicit conservative, noniterative numerical algorithm for the two-dimensional thin layer Navier-Stokes and Euler equations is used to compute the interaction flow-field of a vortex with stationary airfoil. A Lamb-like analytical vortex having a finite core is chosen to interact with a thick (NACA 0012) and a thin (NACA 64A006) airfoil independently in transonic flow. Two different configurations of vortex interaction are studied, viz., (1) when the vortex is fixed at one location in the flowfield, and (2) when the vortex is convecting past the airfoil at freestream velocity. Parallel computations of this interacting flowfield are also done using a version of the Transonic Small Disturbance Code (ATRAN2). A special treatment of the leading edge region for thin airfoils is included in this code. With this, the three methods gave qualitatively similar results for the weaker interactions considered in this study. However, the strongest interactions considered proved to be beyond the capabilities of the small disturbance code. The results also show a far greater influence of the vortex on the airfoil flowfield when the vortex is stationary than when it is convecting with the flow.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 84-0254
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  • 8
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    Transonic interactions of unsteady vortical flows (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Unsteady interactions of strong concentrated vortices, distributed gusts, and sharp-edged gusts with stationary airfoils were analyzed in two-dimensional transonic flow. A simple and efficient method for introducing such vortical disturbances was implemented in numerical codes that range from inviscid transonic small disturbance to thin-layer Navier Stokes. The numerical results demonstrate the large distortions in the overall flow field and in the surface air loads that are produced by various vortical interactions. The results of the different codes are in excellent qualitative agreement, but, as might expected, the transonic small-disturbance calculations are deficient in the important region near the leading edge.
    Keywords: AERODYNAMICS
    Type: NASA-TM-86658 , REPT-85075 , NAS 1.15:86658 , USAAVSCOM-TM-84-A-10 , AD-A152417
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  • 9
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    Numerical simulation of tip vortices of wings in subsonic and transonic flows (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Keywords: AERODYNAMICS
    Type: AD-A204525 , AIAA Journal (ISSN 0001-1452); 26; 1153-116
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  • 10
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    Navier-Stokes calculations of hovering rotor flowfields (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Unsteady, thin-layer Navier-Stokes equations written in rotor coordinates are solved using a partially flux-split, implicit numerical algorithm to calculate the flowfields of a hovering rotor blade at subsonic and transonic conditions. Numerical results are in good agreement with experimental data for both nonlifting and lifting rectangular blades. For the lifting case, the rotor wake effects are modeled by applying a correction to the geometric angle of attack of the blades. Alternate methods of calculating the hovering rotor flowfields in blade-fixed mode that have the same circulation distribution as a hovering blade are explored. All of the results presented in this paper were computed on a Cray-2 supercomputer.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 87-2629 , AD-A204524 , Journal of Aircraft (ISSN 0021-8669); 25; 865-874
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