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  • 1
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    A computational transonic flutter boundary tracking procedure (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An automated flutter boundary tracking procedure is presented for the efficient calculation of transonic flutter boundaries. The new procedure uses aeroelastic responses to march along the boundary by taking steps in speed and Mach number, thereby reducing the number of response calculations previously required to determine a transonic flutter boundary. The tracking procedure reduces computational costs since only two response calculations are required per Mach number and provides a complete boundary in a single job submission. Flutter boundary results are presented for a typical airfoil section oscillating with pitch and plunge degrees of freedom. These transonic flutter boundaries are in good agreement with 'exact' boundaries calculated using the conventional time-marching method. The tracking procedure was also extended to include static aeroelastic twist as a simulation of the static deformation of a wing and thus contains all of the essential features that are required to apply it to practical three-dimensional cases. Application of the procedure is also made to flutter boundaries as a function of structural parameters, the capability of which is useful as a design tool.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-0902
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  • 2
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    Griffith diffusers (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Contoured wall diffusers are designed by using an inverse method. The prescribed wall velocity distribution(s) was taken from the high lift airfoil designed by A. A. Griffith in 1938; therefore, such diffusers are named Griffith diffusers. First the formulation of the inverse problem and the method of solution are outlined. Then the typical contour of a two-dimensional diffuser and velocity distributions across the flow channel at various stations are presented. For a Griffith diffuser to operate as it is designed, boundary layer suction is necessary. Discussion of the percentage of through-flow required to be removed for the purpose of boundary layer control is given. Finally, reference is made to the latest version of a computer program for a two-dimensional diffuser requiring only area ratio, nondimensional length and suction percentage as inputs.
    Keywords: AERODYNAMICS
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  • 3
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    An inverse problem design method for branched and unbranched axially symmetrical ducts (1976)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper concerns the potential flow design of axially symmetrical ducts of both circular and annular cross section with or without wall suction or blowing slots. The objective of the work was to develop a method by which such ducts could be designed with directly prescribed wall pressure variation. Previous axially symmetrical design methods applied only to circular cross sectional ducts and required that the pressure distribution be prescribed along the duct centerline and not along the duct wall. The present method uses an inverse problem approach which extends the method of Stanitz to the axially symmetrical case, and an approximation is used to account for the stagnation point in branched duct designs. Two examples of successful designs of diffusers with suction slots are presented.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 76-422 , Fluid and Plasma Dynamics Conference; Jul 14, 1976 - Jul 16, 1976; San Diego, CA
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  • 4
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    Inverse problem approach to the design of short two-dimensional diffusers. (1972)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Keywords: AERODYNAMICS
    Type: ASME PAPER 72-WA/GT-6 , Winter Annual Meeting of the American Society of Mechanical Engineers; Nov 26, 1972 - Nov 30, 1972; New York, NY
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  • 5
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    A computational transonic flutter boundary tracking procedure (1986)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An automated flutter boundary tracking procedure for the efficient calculation of transonic flutter boundaries is presented. The procedure uses aeroelastic responses to march along the boundary by taking steps in speed and Mach number, thereby reducing the number of response calculations previously required to determine a transonic flutter boundary. Flutter boundary results are presented for a typical airfoil section oscillating with pitch and plunge degrees of freedom. These transonic flutter boundaries are in good agreement with exact boundaries calculated using the conventional time-marching method. The tracking procedure is extended to include static aeroelastic twist as a simulation of the static deformation of a wing and contains all of the essential features that are required to apply it to practical three-dimensional cases. The procedure is also applied to flutter boundaries as a function of structural parameters.
    Keywords: AERODYNAMICS
    Type: NASA-TM-87708 , NAS 1.15:87708 , Structures, Structural Dynamics and Materials Conference; May 19, 1986 - May 21, 1986; San Antonio, TX; United States
    Format: application/pdf
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  • 6
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    Viscous effects on transonic airfoil stability and response (1985)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: An integral boundary layer model coupled to the inviscid XTRAN2L transonic small disturbance code is used to investigate viscous effects on transonic airfoil stability and response. A pulse transfer function analysis is employed for the computation of unsteady transonic airloads which yields forces for a wide range of reduced frequencies in a single flowfield computation. Nonlinear, time-marching aeroelastic solutions are obtained which exhibit the effects of viscosity on airfoil response behavior and flutter. A state-space aeroelastic model using Pade approximants to describe unsteady airloads is used to study viscosity effects on transonic airfoil stability. The state-space dynamic pressure root loci are in good general agreement with time marching damping and frequency estimates.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-0586 , Structures, Structural Dynamics, and Materials Conference; Apr 15, 1985 - Apr 17, 1985; Orlando, FL
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  • 7
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    Viscous effects on transonic airfoil stability and response (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Viscous effects on transonic airfoil stability and response are investigated using an integral boundary layer model coupled to the inviscid XTRAN2L transonic small disturbance code. Unsteady transonic airloads required for stability analyses are computed using a pulse transfer function analysis including viscous effects. The pulse analysis provides unsteady aerodynamic forces for a wide range of reduced frequency in a single flow field computation. Nonlinear time marching aeroelastic solutions are presented which show the effects of viscosity on airfoil response behavior and flutter. Effects of amplitude on time marching responses are demonstrated. A state space aeroelastic model employing Pade approximants to describe the unsteady airloads is used to study the effects of viscosity on transonic airfoil stability. State space dynamic pressure root loci are in good overall agreement with time marching damping and frequency estimates. Parallel sets of results with and without viscous effects reveal the effects of viscosity on transonic unsteady airloads and aeroelastic characteristics of airfoils.
    Keywords: AERODYNAMICS
    Type: NASA-TM-86374 , NAS 1.15:86374 , AIAA PAPER 85-0586 , AIAA/ASME/ASCE/AHS Struct., Struct. Dyn. and Mater. Conf.,; Apr 15, 1985 - Apr 17, 1985; Orlando, FL; United States
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  • 8
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    Inverse design of axisymmetric flow passages using compressible viscous flow theory (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A study reported by Yang and Hudson (1971) was extended by Nelson (1971), who presented a method of inverse design for axisymmetric diffusers. The diffusers obtained with the aid of this method were found to function well under certain conditions, while, for other cases, a modification of the analytical design procedure was required. An outline is provided of the method of inverse solution in simple axisymmetric internal flow passages. Attention is given to governing equations, the method of solution, and examples which illustrate the feasibility of the design procedure. The discussed method, which is based on viscous compressible flow theory, has some limitations. However, it is expected to yield good designs in many practical cases in which the existing design must be modified.
    Keywords: AERODYNAMICS
    Type: Communications in Applied Numerical Methods (ISSN 0748-8025); 2; 83-89
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  • 9
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    Viscous effects on transonic airfoil stability and response (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 23; 361-369
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  • 10
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    Computational transonic flutter boundary tracking procedure (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 25; 263-270
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