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  • 1
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    Vortical sources of aerodynamic force and moment (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is shown that the aerodynamic force and moment can be expressed in terms of vorticity distribution (and entropy variation for compressible flow) on near wake plane, or in terms of boundary vorticity flux on the body surface. Thus the vortical sources of lift and drag are clearly identified, which is the real physical basis of optimal aerodynamic design. Moreover, these sources are highly compact, hence allowing one to concentrate on key local regions of the configuration, which have dominating effect to the lift and drag. A detail knowledge of the vortical low requires measuring or calculating the vorticity and dilatation field, which is however still a challenging task. Nevertheless, this type of formulation has some unique advantages; and how to set up a well-posed problem, in particular how to establish vorticity-dilatation boundary conditions, is addressed.
    Keywords: AERODYNAMICS
    Type: SAE PAPER 892346
    Format: text
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  • 2
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    Streaming effect of wall oscillation to boundary layer separation (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper presents a preliminary theoretical result on the time averaged streaming effect of local forcing excitation to the boundary layer separation from smooth surface. The problem is formulated as a periodic disturbance to a basic steady breakaway separating flow, for which the data are taken from a numerical triple-deck solution. The ratio of Strouhal number St and Reynolds number Re plays an important role, both being assumed sufficiently high. The analytical and numerical results show that this streaming effect is quite strong at proper values of St/Re exp 1/4, which may delay or even suppress the separation.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-0545
    Format: text
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  • 3
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    Review of the physics of enhancing vortex lift by unsteady excitation (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A review aimed at providing a physical understanding of the crucial mechanisms for obtaining super lift by means of unsteady excitations is presented. Particular attention is given to physical problems, including rolled-up vortex layer instability and receptivity, wave-vortex interaction and resonance, nonlinear streaming, instability of vortices behind bluff bodies and their shedding, and vortex breakdown. A general theoretical framework suitable for handling the unsteady vortex flows is introduced. It is suggested that wings with swept and sharp leading edges, equipped with devices for unsteady excitations, could yield the first breakthrough of the unsteady separation barrier and provide super lift at post-stall angle of attack.
    Keywords: AERODYNAMICS
    Type: Progress in Aerospace Sciences (ISSN 0376-0421); 28; 2 19
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  • 4
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    Investigations of flow field perturbations induced on slotted transonic-tunnel walls (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The free-stream interference caused by the flow through the slotted walls of the test sections of transonic wind tunnels has continuously a problem in transonic tunnel testing. The adaptive-wall transonic tunnel is designed to actively control the near-wall boundary conditions by sucking or blowing through the wall. In order to make the adaptive-wall concept work, parameters for computational boundary conditions must be known. These parameters must be measured with sufficient accuracy to allow numerical convergence of the flow field computations and must be measured in an inviscid region away from the model that is placed inside the wind tunnel. The near-wall flow field was mapped in detail using a five-port cone probe that was traversed in a plane transverse to the free-stream flow. The initial experiments were made using a single slot and recent measurements used multiple slots, all with the tunnel empty. The projection of the flow field velocity vectors on the transverse plane revealed the presence of a vortex-like flow with vorticity in the free stream. The current research involves the measurement of the flow field above a multislotted system with segmented plenums behind it, in which the flow is controlled through several plenums simultaneously. This system would be used to control a three-dimensional flow field.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Research Center Wind Tunnel Wall Interference Assessment and Correction, 1983; p 119-142
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  • 5
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    Prospects for computational aerodynamics (1978)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The integral representations approach, for the solution of the Navier-Stokes equations is discussed as well as experience in its development and in applying available finite-difference and finite-element techniques to the treatment of three-dimensional problems, and the computation of turbulent flow. The magnitude of efforts required to develop turbulence models and three-dimensional algorithms indicates that the computational fluid dynamics research must have a broad base. Broader access to modern computing facilities that are in existence within NASA should be promoted for active researchers not directly affiliated with that agency.
    Keywords: AERODYNAMICS
    Type: NASA. Ames Res. Center Future Computer Requirements for Computational Aerodynamics; p 221-227
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  • 6
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    The 3-D wake measurements near a hovering rotor for determining profile and induced drag (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Primarily an experimental effort, this study focuses on the velocity and vorticity fields in the near wake of a hovering rotor. Drag terminology is reviewed, and the theory for separately determining the profile-and-induced-drag components from wake quantities is introduced. Instantaneous visualizations of the flow field are used to center the laser velocimeter (LV) measurements on the vortex core and to assess the extent of the positional mandering of the trailing vortex. Velocity profiles obtained at different rotor speeds and distances behind the rotor blade clearly indicate the position, size, and rate of movement of the wake sheet and the core of the trailing vortex. The results also show the distribution of vorticity along the wake sheet and within the trailing vortex.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3577 , A-950078 , NAS 1.60:3577 , ATCOM-TR-95-A-006
    Format: application/pdf
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  • 7
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    Investigation of transonic flow over segmented slotted wind tunnel wall with mass transfer (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The flowfield on a segmented multi-slotted wind tunnel wall was studied at transonic speeds by measurements in and near the wall layer using five port cone probes. The slotted wall flowfield was observed to be three-dimensional in nature for a relatively significant distance above the slot. The boundary layer characteristics measured on the single slotted wall were found to be very sensitive to the applied suction through the slot. The perturbation in the velocity components generated due to the flow through the slot decay rapidly in the transverse direction. A vortex-like flow existed on the single slotted wall for natural ventilation but diminished with increased suction flow rate. For flow on a segmented multi-slotted wall, the normal velocity component changes were found to be maximum for measurement points located between the segmented slots atop the active chamber. The lateral influence due to applied suction and blowing, through a compartment, exceeded only slightly that in the downstream direction. Limited upstream influence was observed. Influence coefficients were determined from the data in the least-square sense for blowing and suction applied through one and two compartments. This was found to be an adequate determination of the influence coefficients for the range of mass flows considered.
    Keywords: AERODYNAMICS
    Type: NASA-CR-187760 , NAS 1.26:187760 , UTSI-90
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  • 8
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    Considerations of some critical ejector problems (1979)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Some aspects of ejector design and application, including, three dimensional effects and cross flow effects are presented.
    Keywords: AERODYNAMICS
    Type: NASA. Ames Res. Center Workshop on Thrust Augmenting Ejectors; p 363-384
    Format: application/pdf
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  • 9
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    Measurements of compressible secondary flow in a circular S-duct (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper presents the results of an experimental study of secondary flow in a circular cross section 30 deg - 30 deg S-duct with entrance Mach number of 0.6. Local flow velocity vectors have been measured along the length of the duct at six stations. These measurements have been made using a five-port cone probe. Static and total pressure profiles in the transverse planes are obtained from the cone probe measurements. Wall static pressure measurements along three azimuth angles of 0 deg, 90 deg, and 180 deg along the duct are also made. Contour plots presenting the three dimensional velocity field as well as the total- and static-pressure fields are obtained. Surface oil flow visualization technique has been used to provide details of the flow on the S-duct boundaries. The experimental observations have been compared with typical computational results.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 83-1739
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  • 10
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    Three-dimensional flow studies on a slotted transonic wind tunnel wall (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Previously cited in issue 06, p. 799, Accession no. A82-17855
    Keywords: AERODYNAMICS
    Type: (ISSN 0001-1452)
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