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  • 1
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    A summary of current research in rotor unsteady aerodynamics with emphasis on work at Langley Research Center (1973)
    In:  CASI
    Details
    Publikationsdatum: 2011-10-14
    Beschreibung: The basic unsteady aerodynamic environment of the rotary wing is summarized. Some of the observed trends in the state of the art are discussed. Some of the research needs that will require attention are reported. A review of a number of research investigations as a part of a joint NASA/Army rotorcraft project is presented. The research is directed toward achieving a better understanding of rotor unsteady airfoils. The investigations include: (1) rotor maneuver loads; (2) level flight and maneuver wake prediction; (3) tip-vortex flow; (4) blade-vortex interactions; (5) dynamic stall; (6) transient Mach number air loads; and (7) development of variable geometry rotors.
    Schlagwort(e): AERODYNAMICS
    Materialart: AGARD Aerodyn. of Rotary Wings; 20 p
    Format: text
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  • 2
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    Correlation of laser velocimeter measurements over a wing with results of two prediction techniques (1978)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: The flow field at the center line of an unswept wing with an aspect ratio of eight was determined using a two dimensional viscous flow prediction technique for the flow field calculation, and a three dimensional potential flow panel method to evaluate the degree of two dimensionality achieved at the wing center line. The analysis was made to provide an acceptable reference for comparison with velocity measurements obtained from a fringe type laser velocimeter optics systems operating in the backscatter mode in the Langley V/STOL tunnel. Good agreement between laser velocimeter measurements and theoretical results indicate that both methods provide a true representation of the velocity field about the wing at angles of attack of 0.6 and 4.75 deg.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TP-1168 , L-11980
    Format: application/pdf
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  • 3
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    Laser velocimeter survey about a NACA 0012 wing at low angles of attack (1978)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: An investigation was conducted in the Langley V/STOL tunnel with a laser velocimeter to obtain measurements of airflow velocities about a wing at low angles of attack. The applicability of the laser velocimeter technique for this purpose in the V/STOL tunnel was demonstrated in this investigation with measurement precision bias calculated at -1.33 percent to 0.91 percent and a random uncertainty calculated at + or - 0.47 percent. Free stream measurements were obtained with this device and compared with velocity calculations from pitot static probe data taken near the laser velocimeter measurement location. The two measurements were in agreement to within 1 percent. Velocity measurement results about the centerline at 0.6 degrees angle of attack were typically those expected. At 4.75 degrees, the velocity measurements indicated that a short laminar separation bubble existed near the leading edge with an oscillating shear layer.
    Schlagwort(e): RESEARCH AND SUPPORT FACILITIES (AIR)
    Materialart: NASA-TM-74040
    Format: application/pdf
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  • 4
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    Laser velocimeter systems analysis applied to a flow survey above a stalled wing (1977)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: A laser velocimeter operating in the backscatter mode was used to survey the flow above a stalled wing. Polarization was used to separate the two orthogonal velocity components of the fringe-type laser velocimeter, and digital counters were used for data processing. The velocities of the kerosene seed particles were measured with less than 2 percent uncertainty. The particle velocity measurements were collected into histograms. The flow field survey was carried out above an aspect-ratio-8 stalled wing with an NACA 0012 section. The angle of attack was 19.5 deg, the Mach number was 0.49, and the Reynolds number was 1,400,000. The flow field was characterized by the periodic shedding of discrete vortices from near the crest of the airfoil.
    Schlagwort(e): AERONAUTICS (GENERAL)
    Materialart: NASA-TN-D-8408 , L-11105
    Format: application/pdf
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  • 5
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    A laser velocimeter flow survey above a stalled wing (1978)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: A laser velocimeter operating in the backscatter mode was used to survey the flow about a stalled wing installed in the Langley V/STOL tunnel. Mean velocities and magnitudes of velocity fluctuations were calculated from measurements of two orthogonal components of velocity. Free shear mixing layers above and below a large separated flow region were defined. Velocity power spectra were calculated at two points in the flow field. The flow-field survey was carried out about a rectangular aspect-ratio-8 wing with an airfoil section. The wing angle of attack was 19.4 deg, the Mach number was 0.148, and the nominal Reynolds number was 1 x 1 million.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TP-1266 , AVRADCOM-TR-78-50
    Format: application/pdf
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  • 6
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    Comparison of two flow surveys above stalled wings (1979)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: A laser velocimeter (LV) surveyed the flow above two stalled wings. Each wing was tested in a different wind tunnel at different Mach numbers. The low-Mach-number test had an angle of attack of 19.4 deg, 0.15 Mach number, and 1 x 1,000,000 Reynolds number. The mean velocities above the reversed, separated flow were closely modeled by error function profiles. Thus, the flow resembled a turbulent free-shear layer. The high-Mach-number test had an angle of attack of 19.5 deg, 0.49 Mach number, and 1,400,000 Reynolds number. A series of strong, discrete vortices were shed from the airfoil crest at regular intervals. Both tests demonstrated the importance of the unsteady part of the velocities.
    Schlagwort(e): AERODYNAMICS
    Materialart: AIAA PAPER 79-0147 , American Institute of Aeronautics and Astronautics, Aerospace Sciences Meeting; Jan 15, 1979 - Jan 17, 1979; New Orleans, LA
    Format: text
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  • 7
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    A wind-tunnel investigation of parameters affecting helicopter directional control at low speeds in ground effect (1974)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: An investigation was conducted in the Langley full-scale tunnel to measure the performance of several helicopter tail-rotor/fin configurations with regard to directional control problems encountered at low speeds in ground effect. Tests were conducted at wind azimuths of 0 deg to 360 deg in increments of 30 deg and 60 deg and at wind speeds from 0 to 35 knots. The results indicate that at certain combinations of wind speed and wind azimuth, large increases in adverse fin force require correspondingly large increases in the tail-rotor thrust, collective pitch, and power required to maintain yaw trim. Changing the tail-rotor direction of rotation to top blade aft for either a pusher tail rotor (tail-rotor wake blowing away from fin) or a tractor tail rotor (tail-rotor wake blowing against fin) will alleviate this problem. For a pusher tail rotor at 180 deg wind azimuth, increases in the fin/tail-rotor gap were not found to have any significant influence on the overall vehicle directional control capability. Changing the tail rotor to a higher position was found to improve tail-rotor performance for a fin-off configuration at a wind azimuth of 180 deg. A V-tail configuration with a pusher tail rotor with top blade aft direction of rotation was found to be the best configuration with regard to overall directional control capability.
    Schlagwort(e): AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA-TN-D-7694 , L-9325
    Format: application/pdf
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  • 8
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    Fluid mechanics mechanisms in the stall process of airfoils for helicopters (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: Phenomena that control the flow during the stall portion of a dynamic stall cycle are analyzed, and their effect on blade motion is outlined. Four mechanisms by which dynamic stall may be initiated are identified: (1) bursting of the separation bubble, (2) flow reversal in the turbulent boundary layer on the airfoil upper surface, (3) shock wave-boundary layer interaction behind the airfoil crest, and (4) acoustic wave propagation below the airfoil. The fluid mechanics that contribute to the identified flow phenomena are summarized, and the usefulness of a model that incorporates the required fluid mechanics mechanisms is discussed.
    Schlagwort(e): AERODYNAMICS
    Materialart: Symposium on Numerical and Physical Aspects of Aerodynamic Flows; Jan 19, 1981 - Jan 21, 1981; Long Beach, CA
    Format: text
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  • 9
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    Fluid mechanics mechanisms in the stall process of helicopters (1981)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: Recent experimental results from airfoils in the Mach number, Reynolds number, or reduced frequency ranges typical of helicopter rotor blades have identified the most influential flow mechanisms in the dynamic stall process. The importance of secondary shed vortices, downstream wake action, and the flow in the separated region is generally acknowledged but poorly understood. By means of surface pressure cross-correlations and flow field measurements in static stall, several new hypotheses have been generated. It is proposed that vortex shedding may be caused by acoustic disturbances propagating forward in the lower (pressure) surface boundary layer, that wake closure is a misnomer, and that the shed vortex leaves a trail of vorticity that forms a turbulent free shear layer. The known dynamic stall flow mechanisms are reviewed and the potential importance of recently proposed and hypothetical flow phenomena with respect to helicopter blade aeroelastic response are assessed.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-81956 , USAAVRADCOM-TR-81-B-1 , Symp. on Numerical and Phys. Aspects of Aerodyn. Flows; Jan 19, 1981 - Jan 21, 1981; Long Beach, CA; United States
    Format: application/pdf
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