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  • AERODYNAMICS  (8)
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  • 1
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    Aerodynamic control using forebody strakes (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Aerodynamic control using a rotatable, miniature nose-tip strake system was investigated in a water tunnel with a forebody model. Flow visualization and yawing moment measurements were performed. The results show that the system was highly effective in controlling the forebody vortices and producing controlled yawing moments at moderate-to-high angles of attack. In comparison with the forebody strakes used in several previous studies, the system can potentially be substantially smaller in size, simpler in operation, and effective over wide ranges of angles of attack and sideslip.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-0618
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Aerodynamic control using forebody blowing and suction (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Aerodynamic control using pneumatic forebody flow control was studied. Three methods of control were investigated: (1) blowing from a localized jet, (2) blowing from a slot, and (3) surface suction. Flow visualization and yawing moment measurements were performed on F/A-18 models in a water tunnel. The results show that all the methods were effective in controlling the forebody flow over a wide range of angles of attack and sideslip. The advantages and limitations of each of the control methods were discussed. The experiments suggested that all the control methods work basically on the principle of separation control. Based on the results of the water tunnel tests, the blowing or suction mass flow requirements appear to be within the limits of typical engine-bleed available from a modern fighter engine.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-0619
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Visualization of leading edge vortices on a series of flat plate delta wings (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A summary of flow visualization data obtained as part of NASA Grant NAG2-258 is presented. During the course of this study, many still and high speed motion pictures were taken of the leading edge vortices on a series of flat plate delta wings at varying angles of attack. The purpose is to present a systematic collection of photographs showing the state of vortices as a function of the angle of attack for the four models tested.
    Keywords: AERODYNAMICS
    Type: NASA-CR-4320 , A-90094 , NAS 1.26:4320
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Aerodynamic control of NASP-type vehicles through vortex manipulation. Volume 3: Wing rock experiments (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Free-to-roll tests were conducted in water and wind tunnels in an effort to investigate the mechanisms of wing rock on a NASP-type vehicle. The configuration tested consisted of a highly-slender forebody and a 78 deg swept delta wing. In the water tunnel test, extensive flow visualization was performed and roll angle histories were obtained. In the wind tunnel test, the roll angle, forces and moments, and limited forebody and wing surface pressures were measured during the wing rock motion. A limit cycle oscillation was observed for angles of attack between 22 deg and 30 deg. In general, the experiments confirmed that the main flow phenomena responsible for the wing-body-tail wing rock are the interactions between the forebody and the wing vortices. The variation of roll acceleration (determined from the second derivative of the roll angle time history) with roll angle clearly slowed the energy balance necessary to sustain the limit cycle oscillation. Different means of suppressing wing rock by controlling the forebody vortices using small blowing jets were also explored. Steady blowing was found to be capable of suppressing wing rock, but significant vortex asymmetrices are created, causing the model to stop at a non-zero roll angle. On the other hand, alternating pulsed blowing on the left and right sides of the fore body was demonstrated to be a potentially effective means of suppressing wing rock and eliminating large asymmetric moments at high angles of attack.
    Keywords: AERODYNAMICS
    Type: NASA-CR-177626 , A-93138 , NAS 1.26:177626
    Format: application/pdf
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  • 5
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    Aerodynamic control of NASP-type vehicles through Vortex manipulation. Volume 1: Static water tunnel tests (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Water tunnel tests were conducted on a NASP-type configuration to evaluate different pneumatic Forebody Vortex Control (FVC) methods. Flow visualization and yawing moment measurements were performed at angles of attack from 0 deg to 30 deg. The pneumatic techniques tested included jet and slot blowing. In general, blowing can be used efficiently to manipulate the forebody vortices at angles of attack greater than 20 deg. These vortices are naturally symmetric up to alpha = 25 deg and asymmetric between 25 deg and 30 deg angle of attack. Results indicate that tangential aft jet blowing is the most promising method for this configuration. Aft jet blowing produces a yawing moment towards the blowing side and the trends with blowing rate are well behaved. The size of the nozzle is not the dominant factor in the blowing process; the change in the blowing 'momentum,' i.e., the product of the mass flow rate and the velocity of the jet, appears to be the important parameter in the water tunnel (incompressible and unchoked flow at the nozzle exit). Forward jet blowing is very unpredictable and sensitive to mass flow rate changes. Slot blowing (with the exception of very low blowing rates) acts as a flow 'separator'; it promotes early separation on the blow side, producing a yawing moment toward the non-blowing side for the C(sub mu) range investigated.
    Keywords: AERODYNAMICS
    Type: NASA-CR-177626-VOL-1 , A-93138-VOL-1 , NAS 1.26:177626-VOL-1
    Format: application/pdf
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  • 6
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    An experimental investigation of delta wing vortex flow with and without external jet blowing (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A visual and quantitative study of the vortex flow field over a 70-deg delta wing with an external jet blowing parallel to and at the leading edge was conducted. In the experiment, the vortex core was visually marked with TiCl4, and LDA was used to measure the velocity parallel and normal to the wing surface. It is found that jet blowing moved vortex breakdown farther downstream from its natural position and influenced the breakdown characteristics.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-0084
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Flow visualization study of delta wings in wing-rock motion (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Water tunnel flow visualizations have been conducted for the wing-rock phenomenon in the cases of models having different leading-edge sweeps and roundness. Wing rock, which is noted to occur in the absence of asymmetric vortex liftoff, vortex breakdown, and static hysteresis, is seen to be initiated by flowfield asymmetries that are induced by flow disturbances and vortex interactions near the apex region; one vortex is thereby strengthened while the other is weakened, inducing a roll moment. Leading-edge roundness decreases vortex strength and reduces vortex spacing, reducing the tendency to wind rock and coupled vortex motions at higher angles-of-attack.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-2187 , AIAA Applied Aerodynamics Conference; Jul 31, 1989 - Aug 02, 1989; Seattle, WA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Effect of leading edge roundness on a delta wing in wing-rock motion (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The effect of wing leading-edge roundness on wing rock was investigated using flow visualization in a water tunnel. Eighty degree delta wing models were tested on free-to-roll and forced oscillation rigs. The onset of wing rock was delayed by increasing the roundness of the leading edges. The wing rock amplitude and frequency results suggested that damping was increased at lower angles of attack but reduced at higher angles of attack. Vortex lift-off and vortex breakdown, especially during dynamic situations, were strongly affected by the leading edge roundness. Different forms of wing rock motion could be sustained by combinations of vortex breakdown and vortex lift-off. Behaviors of the wing and vortex motions were explained by the influence of leading edge roundness on the separation location, vortex trajectory, and vortex breakdown.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 90-3080 , AIAA Applied Aerodynamics Conference; Aug 20, 1990 - Aug 22, 1990; Portland, OR; United States
    Format: text
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