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  • 1
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    Semi-empirical model for prediction of unsteady forces on an airfoil with application to flutter (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A semi-empirical model is described for predicting unsteady aerodynamic forces on arbitrary airfoils under mildly stalled and unstalled conditions. Aerodynamic forces are modeled using second order ordinary differential equations for lift and moment with airfoil motion as the input. This model is simultaneously integrated with structural dynamics equations to determine flutter characteristics for a two degrees-of-freedom system. Results for a number of cases are presented to demonstrate the suitability of this model to predict flutter. Comparison is made to the flutter characteristics determined by a Navier-Stokes solver and also the classical incompressible potential flow theory.
    Keywords: AERODYNAMICS
    Type: NASA-TM-105414 , E-6820 , NAS 1.15:105414
    Format: application/pdf
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  • 2
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    Reduced order models for nonlinear aerodynamics (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Reduced order models are needed for reliable, efficient and accurate prediction of aerodynamic forces to analyze fluid structure interaction problems in turbomachinery, including propfans. Here, a finite difference, time marching Navier-Stokes code is validated for unsteady airfoil motion by comparing results with those from classical potential flow. The Navier-Stokes code is then analyzed for calculation of primitive and exact estimates of eigenvalues and eigenvectors associated with fluid-airfoil interaction. A variational formulation for the Euler equations and Navier-Stokes equations will be the basis for reduction of order through an eigenvector transformation.
    Keywords: AERODYNAMICS
    Type: NASA, Lewis Research Center, Lewis Structures Technology, 1988. Volume 1: Structural Dynamics; p 299-308
    Format: application/pdf
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  • 3
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    Eigenvalue calculation procedure for an Euler/Navier-Stokes solver with application to flows over airfoils (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A Lanczos procedure is presently applied to a Navier-Stokes (N-S) solver for eigenvalues and eigenvectors associated with the small-perturbation analysis of the N-S equations' finite-difference representation for airfoil flows; the matrix used is very large, sparse, real, and nonsymmetric. The Lanczos procedure is shown to furnish complete spectral information for the eigenvalues, as required for transient-stability analysis of N-S solvers.
    Keywords: AERODYNAMICS
    Type: Journal of Computational Physics (ISSN 0021-9991); 97; 398-413
    Format: text
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  • 4
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    Role of artificial viscosity in Euler and Navier-Stokes solvers (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A method is proposed to determine directly the amount of artificial viscosity needed for stability using an eigenvalue analysis for a finite difference representation of the Navier-Stokes equations. The stability and growth of small perturbations about a steady flow over airfoils are analyzed for various amounts of artificial viscosity. The eigenvalues were determined for a small time-dependent perturbation about a steady inviscid flow over an NACA 0012 airfoil at a Mach number of 0.8 and angle of attack of 0 deg. The method has been applied to inviscid flows here, but as discussed is also applicable to viscous flows. The movement of the eigenvalue constellation with respect to the amount of artificial viscosity is studied. The stability boundaries as a function of the amount of artificial viscosity from both the eigenvalue analysis and the time-marching scheme are also presented. The eigenvalue procedure not only allows for determining the effect of varying amounts of artificial viscosity, but also for the effects of different forms of artificial viscosity.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 555-559
    Format: text
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  • 5
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    Semi-empirical model for prediction of unsteady forces on an airfoil with application to flutter (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A semi-empirical model is described for predicting unsteady aerodynamic forces on arbitrary airfoils under mildly stalled and unstalled conditions. Aerodynamic forces are modeled using second order ordinary differential equations for lift and moment with airfoil motion as the input. This model is simultaneously integrated with structural dynamics equations to determine flutter characteristics for a two degrees-of-freedom system. Results for a number of cases are presented to demonstrate the suitability of this model to predict flutter. Comparison is made to the flutter characteristics determined by a Navier-Stokes solver and also the classical incompressible potential flow theory.
    Keywords: AERODYNAMICS
    Type: Journal of Fluids and Structures (ISSN 0889-9746); 7; 1; p. 87-103.
    Format: text
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  • 6
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    On the role of artificial viscosity in Navier-Stokes solvers (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A method is proposed to determine directly the amount of artificial viscosity needed for stability using an eigenvalue analysis for a finite difference representation of the Navier-Stokes equations. The stability and growth of small perturbations about a steady flow over the airfoils are analyzed for various amounts of artificial viscosity. The eigenvalues were determined for a small perturbation about a steady inviscid flow over a NACA 0012 airfoil at a Mach number of 0.8 and angle of attack of 0 degrees. The movement of the eigenvalue constellation with respect to the amount of artificial viscosity is studied. The stability boundries as a function of the amount of artificial viscosity from both the eigenvalue analysis and the time marching scheme are also presented. This procedure not only allows for determining the effect of varying amounts of artificial viscosity, but also for the effects of different forms of terms for artificial viscosity.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-1947 , AIAA Computational Fluid Dynamics Conference; Jun 13, 1989 - Jun 15, 1989; Buffalo, NY; United States
    Format: text
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