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  • 1
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    Control of turbulent separated flow over a rearward-facing ramp using longitudinal grooves (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Aircraft (ISSN 0021-8669); 27; 283-285
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  • 2
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    Turbulent roughness drag due to surface waviness at low roughness Reynolds numbers (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The current investigation has the objective to provide data which will make it possible to obtain a better estimate regarding the roughness drag for surface waviness. The data employed for this investigation were acquired in connection with a wavy wall study which was conducted as part of an overall program to reduce the skin friction of turbulent boundary layers in external flows. The results of the present investigation show that the low-speed roughness drag of small-amplitude sinusoidal wave trains having wavelengths of the order of the boundary-layer thickness is not only a function of h/lambda (h = total wave height, lambda = wavelength), but, in addition, is also a function of the roughness Reynolds number.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Aircraft (ISSN 0021-8669); 21; 978
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  • 3
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    Wall temperature control of low-speed body drag (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The use of thermal means to control drag under turbulent boundary layer conditions is examined. Numerical calculations are presented for both skin friction and (unseparated) pressure drag for turbulent boundary-layer flows over a fuselage-like body with wall heat transfer. In addition, thermal control of separation on a bluff body is investigated. It is shown that a total drag reduction of up to 20 percent can be achieved for wall heating with a wall-to-total-freestream temperature ratio of 2. For streamlined slender bodies, partial wall heating of the forebody can produce almost the same order of total drag reduction as the full body heating case. For bluff bodies, the separation delay from partial wall cooling of the afterbody is approximately the same as for the fully cooled body.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Aircraft (ISSN 0021-8669); 23; 93
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  • 4
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    Exploratory study of vortex-generating devices for turbulent flow separation control (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Flow phenomena and the relative performance associated with several devices for controlling turbulent separated flow were investigated at low speeds. Vortex-generating devices examined included: submerged vortex generators (Wheeler doublet and wishbone types), spanwise cylinders, large-eddy breakup devices (LEBU) at small angle of attack (alpha), and vortex-generator jets (VGJ). Dye flow visualization tests in a water tunnel indicated that wishbone vortex generators in the forward orientation shed horseshoe vortices; wishbone vortex generators oriented in the reverse direction and doublet vortex generators shed streamwise counterrotating vortices; a spanwise cylinder located near the wall and LEBUs at alpha = -10 deg produced eddies which rotated with the same sign as the mean vorticity in a turbulent boundary layer; and the most effective VGJs produced streamwise corotating vortices. Comparative wind tunnel tests conducted on a curved backward-facing ramp indicated that transferring momentum from the outer region of a turbulent boundary layer by embedded streamwise vortices is more effective than by transverse vortices for separation control applications.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 91-0042
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  • 5
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    Investigation of several passive and active methods for turbulent flow separation control (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Relative performance of several passive and active methods for controlling two-dimensional turbulent separated flow associated with a curved backward-facing ramp were investigated at low speeds. Surface static pressure measurement and oil flow visualization results indicate that submerged vortex generators, vortex generator jets, elongated arches at +-alpha, and large-eddy breakup devices at +-alpha placed near the baseline separation location reduce flow separation and increase pressure recovery. Spanwise cylinders reduce flow separation but decrease pressure recovery downstream. Arches with alpha = 0 deg, Helmholtz resonators, and Viets' fluidic flappers examined so far have no significant effect in reducing separation. Wall cooling computation indicates that separation delay on a partially cooled ramp is nearly the same as on a fully-cooled ramp while minimizing the frictional drag increase associated with the wall cooling process.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 90-1598
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  • 6
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    Jet vortex generators for turbulent flow separation control (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A parametric study was performed with jet vortex generators to determine their effectiveness in controlling flow separation associated with low-speed turbulent flow over a two-dimensional rearward-facing ramp. Results indicate that flow separation control can be accomplished with the level of control achieved being a function of jet speed, jet orientation (with respect to the free-stream direction), and orifice pattern (double row of jets vs. single row). Compared to slot blowing, jet vortex generators can provide an equivalent level of flow control over a larger spanwise region (for constant jet flow area and speed).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 7
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    Electrical impedance imaging in two-phase, gas-liquid flows: 1. Initial investigation (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The determination of interfacial area density in two-phase, gas-liquid flows is one of the major elements impeding significant development of predictive tools based on the two-fluid model. Currently, these models require coupling of liquid and vapor at interfaces using constitutive equations which do not exist in any but the most rudimentary form. Work described herein represents the first step towards the development of Electrical Impedance Computed Tomography (EICT) for nonintrusive determination of interfacial structure and evolution in such flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Pennsylvania State Univ., Third International Conference on Inverse Design Concepts and Optimization in Engineering Sciences (ICIDES-3); p 111-122
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  • 8
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    Drag of two-dimensional small-amplitude symmetric and asymmetric wavy walls in turbulent boundary layers (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Included are results of an experimental investigation of low-speed turbulent flow over multiple two-dimensional transverse rigid wavy surfaces having a wavelength on the order of the boundary-layer thickness. Data include surface pressure and total drag measurements on symmetric and asymmetric wall waves under a low-speed turbulent boundary-layer flow. Several asymmetric wave configurations exhibited drag levels below the equivalent symmetric (sine) wave. The experimental results compare favorably with numerical predictions from a Reynolds-averaged Navier-Stokes spectral code. The reported results are of particular interest for the estimation of drag, the minimization of fabrication waviness effects, and the study of wind-wave interactions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TP-2318 , L-15761 , NAS 1.60:2318
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  • 9
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    Stability of mixed time integration schemes for transient thermal analysis (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A current research topic in coupled-field problems is the development of effective transient algorithms that permit different time integration methods with different time steps to be used simultaneously in various regions of the problems. The implicit-explicit approach seems to be very successful in structural, fluid, and fluid-structure problems. This paper summarizes this research direction. A family of mixed time integration schemes, with the capabilities mentioned above, is also introduced for transient thermal analysis. A stability analysis and the computer implementation of this technique are also presented. In particular, it is shown that the mixed time implicit-explicit methods provide a natural framework for the further development of efficient, clean, modularized computer codes.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Numerical Heat Transfer; 5; Apr
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  • 10
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    Turbulent flow separation control through passive techniques (1989)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Several passive separation control techniques for controlling moderate two-dimensional turbulent flow separation over a backward-facing ramp are studied. Small transverse and swept grooves, passive porous surfaces, large longitudinal grooves, and vortex generators were among the techniques used. It was found that, unlike the transverse and longitudinal grooves of an equivalent size, the 45-deg swept-groove configurations tested tended to enhance separation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 89-0976
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