Author: Michael S. Francis
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ISBN:
Category : Aerofoils
Languages : en
Pages :
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"The results of an experimental investigation of airfoil dynamic stall involving large amplitude pitching motions are described. The discussion is focused on constant pitch rate motion histories. Measurements of unsteady surface pressure distributions for both NACA 0012 and NACA 64 sub 1 A012(13) profiles have been employed to infer the onset and evolution of an energetic leading edge separation vortex over a wide range of flow and motion conditions. These data have also been integrated to provide estimates of the time histories of the lift, pressure drag and moment coefficients. The effectiveness of the various motions for achieving lift enhancement has been determined through the introduction of a dimensionless impulse parameter which accounts for both the magnitude and duration of the additional lift increment during the post-stall period."--Abstract, report documention p.
Author: Michael S. Francis
Publisher:
ISBN:
Category :
Languages : en
Pages : 158
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The results of an experimental investigation of airfoil dynamic stall involving large amplitude pitching motions are described. The discussion is focused on constant pitch rate motion histories. Measurements of unsteady surface pressure distributions for both NACA 0012 and NACA 64 sub 1 A012(13) profiles have been employed to infer the onset and evolution of an energetic leading edge separation vortex over a wide range of flow and motion conditions. These data have also been integrated to provide estimates of the time histories of the lift, pressure drag and moment coefficients. The effectiveness of the various motions for achieving lift enhancement has been determined through the introduction of a dimensionless impulse parameter which accounts for both the magnitude and duration of the additional lift increment during the post-stall period. (Author).
Author:
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ISBN:
Category :
Languages : en
Pages : 201
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In the first part of this study, surface shear-stress measurements were obtained on a NACA 0012 airfoil model, undergoing a pitch-up motion from 0 deg to 43 deg angle of attack at a constant rate using an array of surface-mounted hot-film sensors. Dominant features in these data and in the standard deviations computed from these data were examined and related to events in the development and evolution of the unsteady separation over the suction surface. Results were compared with well-known features of the dynamic stall process seen in the surface-pressure distributions. Trends in the behavior of these features are presented for a range of non-dimensional pitch rates and chord Reynolds numbers. Significant changes were seen in the behavior of these features at high Reynolds numbers. The results suggest that these changes are due to transition in the shear layer at high pitch rates and quasi-steady behavior at low pitch rates. In the second pan of this study, large amplitude sinusoidal motions were investigated for a wide range of Reynolds numbers and reduced frequencies. A combination of unsteady pressure and shear-stress data at the surface of the airfoil provided detailed information about the development and evolution of the flowfield. In particular, the formation of the dynamic stall vortex (DSV) during the upstroke of the motion profile was examined in detail as well as the reattachment process during the downstroke of the motion profile. Significant changes in behavior were seen with changing Reynolds number, reduced frequency, and amplitude of oscillation. The mean angle did not affect the development of the DSV except at the highest reduced frequency (k=0.4). Amplitude of oscillation did not affect the development of the reattachment process.
Author:
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Category :
Languages : en
Pages : 64
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Author: W. J. McCroskey
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ISBN:
Category :
Languages : en
Pages : 38
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Stall and its consequences are fundamentally important to the design and operation of flight vehicles. A certain degree of unsteadiness always accompanies the flow over an airfoil or other streamlined body at high angle of attack, but the stall of a lifting surface undergoing unsteady motion is even more complex than static stall. Dynamic stall remains a major unsolved problem with a variety of current applications in aeronautics, hydrodynamics, and wind engineering. This report summarizes the main physical features of the phenomenon and the attempts that have been made to predict it. The information presented is drawn mainly from recent review articles and investigations by the author and his colleagues. Since a large fraction of the existing knowledge has come from experimental research, the details of dynamic stall are discussed principally in physical terms.
Author:
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Category : Aeronautics
Languages : en
Pages : 994
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Author:
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Category :
Languages : en
Pages : 33
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This research program investigated the physical mechanisms involved in the onset of leading edge separation when airfoils pitch to high angles of attack. Both constant pitch rate and variable pitch rate motions were considered. The highlights of results from a combined experimental and computational effort are described in this report. The conclusions from this research indicate the need for boundary-layer resolved measurements of the flow behavior near the leading edge and the evolution of the reverse flow regions on the suction surface. Furthermore, the deliberate shaping of the pitch trajectory for the purpose of optimization of separation delay is suggested as one way to manage the flow and aerodynamic behavior of an airfoil. Dynamic Stall, Unsteady Separation.
Author: K. W. McAlister
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ISBN:
Category : Aerofoils
Languages : en
Pages : 80
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Author: W. Geissler
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Category : Boundary layer
Languages : en
Pages : 52
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Author: John A. Ekaterinaris
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Category :
Languages : en
Pages :
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