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  • 1
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    Dynamic stall of an oscillating airfoil (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Unsteady separated boundary layers and wakes were studied by investigating flow past an oscillating airfoil which in part models the retreating blade stall on the helicopters. The Navier-Stokes equations in terms of the vorticity and stream function for laminar flow were solved to determine the flow field around a modified NACA 0012 airfoil. After a fully developed flow was determined at zero incidence, the airfoil was oscillated in pitch through an angle of attack range from 0 deg to 20 deg. The computed streamlines during this pitch-up motion are in qualitative agreement with the trajectories of air bubbles observed in water tunnel experiments conducted with a NACA 0012 airfoil under the same conditions. During the pitch-down motion of the airfoil, the computed flow patterns cannot be compared with the experiments because the trajectories of air bubbles intersect.
    Keywords: AERODYNAMICS
    Type: AGARD Unsteady Aerodyn.; 32 p
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Starting vortex, separation bubbles and stall - A numerical study of laminar unsteady flow around an airfoil (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The stalling characteristics of an airfoil in a laminar viscous incompressible fluid are investigated. The governing equations in terms of the vorticity and stream function are solved using an implicit finite-difference scheme and point successive relaxation procedure. The development of the impulsively started flow, the initial generation of circulation, and the behavior of the forces at large times are studied. Following the impulsive start, the lift is at first very large and then it rapidly drops. The subsequent growth of circulation and lift is associated with the starting vortex. After incipient separation, the lift increases owing to enlargement of the separation bubble and intensification of the flow rotation in it. The extension of this bubble beyond the trailing edge causes it to rupture and brings about the stalling characteristics of the airfoil. Subsequently, new bubbles are formed near the upper surface of the airfoil and are swept away. The behavior of the lift acting on the airfoil is explained in terms of the strength and sense of these bubbles.
    Keywords: AERODYNAMICS
    Type: Journal of Fluid Mechanics; 67; Jan. 28
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Analysis of the separated boundary layer flow on the surface and in the wake of blunt trailing edge airfoils (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The viscous flow phenomena associated with sharp and blunt trailing edge airfoils were investigated. Experimental measurements were obtained for a 17 percent thick, high performance GAW-1 airfoil. Experimental measurements consist of velocity and static pressure profiles which were obtained by the use of forward and reverse total pressure probes and disc type static pressure probes over the surface and in the wake of sharp and blunt trailing edge airfoils. Measurements of the upper surface boundary layer were obtained in both the attached and separated flow regions. In addition, static pressure data were acquired, and skin friction on the airfoil upper surface was measured with a specially constructed device. Comparison of the viscous flow data with data previously obtained elsewhere indicates reasonable agreement in the attached flow region. In the separated flow region, considerable differences exist between these two sets of measurements.
    Keywords: AERODYNAMICS
    Type: NASA-CR-145202
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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