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  • AERODYNAMICS  (8)
  • Aerodynamics  (4)
  • 1
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    Unsteady aerodynamic behavior of an airfoil with and without a slat (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Unsteady flow behavior and load characteristics of a 2D VR-7 airfoil with and without a leading-edge slat were studied in the water tunnel of the Aeroflightdynamics Directorate, NASA Ames Research Center. Both airfoils were oscillated sinusoidally between 5 and 25 deg at Re = 200,000 to obtain the unsteady lift, drag, and pitching moment data. A fluorescent dye was released from an orifice located at the leading edge of the airfoil for the purpose of visualizing the boundary layer and wake flow. The flowfield and load predictions of an incompressible Navier-Stokes code based on a velocity-vorticity formulation were compared with the test data. The test and predictions both confirm that the slatted VR-7 airfoil delays both static and dynamic stall as compared to the VR-7 airfoil alone.
    Keywords: AERODYNAMICS
    Type: Computers & Fluids (ISSN 0045-7930); 22; 4-5; p. 529-547.
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    NASA TECHNICAL REPORTS
  • 2
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    Effect of wake structure on blade-vortex interaction phenomena: Acoustic prediction and validation (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: During the Higher Harmonic Control Aeroacoustic Rotor Test, extensive measurements of the rotor aerodynamics, the far-field acoustics, the wake geometry, and the blade motion for powered, descent, flight conditions were made. These measurements have been used to validate and improve the prediction of blade-vortex interaction (BVI) noise. The improvements made to the BVI modeling after the evaluation of the test data are discussed. The effects of these improvements on the acoustic-pressure predictions are shown. These improvements include restructuring the wake, modifying the core size, incorporating the measured blade motion into the calculations, and attempting to improve the dynamic blade response. A comparison of four different implementations of the Ffowcs Williams and Hawkings equation is presented. A common set of aerodynamic input has been used for this comparison.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110825 , NAS 1.15:110825 , AD-A294477
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    NASA TECHNICAL REPORTS
  • 3
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    Prediction and measurement of blade-vortex interaction loading (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An extensive quantity of airload measurements was obtained for a pressure-instrumented model of the BO-105 main rotor for a large number of higher-harmonic control (HHC) settings at Duits-Nederlandse Wind Tunnel (DNW). The wake geometry, vortex strength, and vortex core size were also measured through a laser light sheet technique and LDV. These results are used to verify the BVI airload prediction methodologies developed by AFDD, DLR, NASA Langley, and ONERA. The comparisons show that an accurate prediction of the blade motion and the wake geometry is the most important aspect of the BVI airload predictions.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110824 , NAS 1.15:110824 , AD-A294468
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  • 4
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    Characteristics of deformable leading edge for high performance helicopter rotor (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The deformable leading edge (DLE) concept to improve the blade capability in lift, drag and pitching moments has been investigated for the purpose of meeting new rotor maneuverability and susceptibility requirements. The advantages and disadvantages of this concept have been carefully examined with limited computational and experimental results. This work showed that this concept achieves a substantial improvement in lift capability and also reduces the drag and pitching moment at the same time. Effects of various parameters, such as Reynolds number, reduced frequency, mean angle of oscillation, and airfoil shape, on the performance of these airfoils were also investigated.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 93-3526 , AD-A268648 , In: AIAA Applied Aerodynamics Conference, 11th, Monterey, CA, Aug. 9-11, 1993, Technical Papers. Pt. 2 (A93-47201 19-02); p. 968-988.
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  • 5
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    Euler solution of the transonic flow for a helicopter rotor (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A new method is presented for calculating the quasi-steady transonic flow over a lifting or nonlifting rotor blade in both hover and forward flight by using Euler equations. The approach is to solve the Euler equations in a rotor-fixed frame of reference using a finite volume method. A computer program was developed and was then verified by comparison with wind-tunnel data. In all cases considered, good agreement was found with available experimental data.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 87-0523
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  • 6
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    Dynamic stall study of a multi-element airfoil (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Unsteady flow behavior and load characteristics of a VR-7 airfoil with and without a slat were studied in the water tunnel of the Aeroflightdynamics Directorate, NASA Ames Research Center. Both airfoils were oscillated sinusoidally between 5 and 25 degrees at a Reynolds number of 200,000 to obtain the unsteady lift, drag and pitching moment data. A fluorescing dye was released from an orifice located at the leading edge of the airfoil for the purpose of visualizing the boundary layer and wake flow. The flow field and load predictions of an incompressible Navier-Stokes code based on a velocity-vorticity formulation were compared with the test data. The test and predictions both confirm that the slatted VR-7 airfoil delays both static and dynamic stall as compared to the VR-7 airfoil alone.
    Keywords: AERODYNAMICS
    Type: ; 19 p.|AAAF, European Rotorcraft Forum; Sept. 15-18, 1992; Avignon; France
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    NASA TECHNICAL REPORTS
  • 7
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    Rotor Wake Vortex Definition: Initial Evaluation of 3-C PIV Results of the Hart-II Study (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An initial evaluation is made of extensive three-component (3C) particle image velocimetry (PIV) measurements within the wake across a rotor disk plane. The model is a 40 percent scale BO-105 helicopter main rotor in forward flight simulation. This study is part of the HART II test program conducted in the German-Dutch Wind Tunnel (DNW). Included are wake vortex field measurements over the advancing and retreating sides of the rotor operating at a typical descent landing condition important for impulsive blade-vortex interaction (BVI) noise. Also included are advancing side results for rotor angle variations from climb to steep descent. Using detailed PIV vector maps of the vortex fields, methods of extracting key vortex parameters are examined and a new method was developed and evaluated. An objective processing method, involving a center-of-vorticity criterion and a vorticity 'disk' integration, was used to determine vortex core size, strength, core velocity distribution characteristics, and unsteadiness. These parameters are mapped over the rotor disk and offer unique physical insight for these parameters of importance for rotor noise and vibration prediction.
    Keywords: Aerodynamics
    Type: 28th European Rotorcraft Forum; Sep 17, 2002 - Sep 20, 2002; Bristol, England; United Kingdom
    Format: application/pdf
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  • 8
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    The Prediction of Transonic Flows on an Advancing Rotor (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The object of this investigation was to find and demonstrate a means of performing efficient finite-difference computations of rotor loading for a trimmed rotor in high-speed, forward flight. The essence of the scheme that was developed is a loose-coupled iteration procedure between a finite difference and a comprehensive integral rotor code. The coupling involves a transfer of appropriate load and inflow data on the advancing side between the two codes such that consistency maintained. Sample computations, including a limited comparison with model rotor data, are presented. The scheme converges rapidly. However, even one iteration with this scheme can provide sufficient accuracy for many purposes.
    Keywords: Aerodynamics
    Type: May 01, 1984; Arlington, VA; United States
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  • 9
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    Forced Diffusion of Trailing Vorticity from a Hovering Rotor (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: A small turbulence generating device was Attached near the tip of a hovering rotor blade In order to alter the structure of the trailing vortex. Stereo particle image velocimetry (PIV) images were used to quantify the wake behind the rotor blade during the first revolution. An analysis of the 3D-velocity field includes a method for accounting for vortex wander. The results show that a major change in the size and intensity of the trailing vortex can be achieved.
    Keywords: Aerodynamics
    Type: American Helicopter Society 57th Annual Forum and Technology Display; May 09, 2001 - May 11, 2001; Washington, DC; United States
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  • 10
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    Numerical study of multi-element airfoil aerodynamics (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: Unsteady flowfields around oscillating Boeing VR7 airfoil with and without a leading-edge slat were numerically investigated by a novel zonal method using a conformal mapping technique. Numerical aero-dynamic hysteresis loops show that the leading-edge slat prevents the airfoil dynamic stall at reduced frequency of 0.15, Reynolds number of 1 million, and the oscillation range of 5 deg to 25 deg.
    Keywords: AERODYNAMICS
    Type: ; : Algorithmic trends
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