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  • 1980-1984  (4)
  • 1
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    Unsteady behavior of a reattaching shear layer (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A detailed investigation of the unsteadiness in a reattaching, turbulent shear layer is reported. Laser-Doppler velocimeter measurements were conditionally sampled on the basis of instantaneous flow direction near reattachment. Conditions of abnormally short reattachment and abnormally long reattachment were considered. Ensemble-averaging of measurements made during these conditions was used to obtain mean velocities and Rreynolds stresses. In the mean flow, conditional streamlines show a global change in flow pattern which correlates with wall-flow direction. This motion can loosely be described as a 'flapping' of the shear layer. Tuft probes show that the flow direction reversals occur quite randomly and are shortlived. Streses shown also vary with the change in flow pattern. Yet, the global'flapping' motion does not appear to contribute significantly to the stress in the flow. A second type of unsteady motion was identified. Spectral analysis of both wall static pressure and streamwise velocity shows that most of the energy in the flow resides in frequencies that are significantly lower than that of the turbulence. The dominant frequency is at a Strouhal number equal to 0.2, which is the characteristic frequency of roll-up and pairing of vortical structure seen in free shear layers. It is conjectured that the 'flapping' is a disorder of the roll-up and pairing process occurring in the shear layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 83-1712
    Format: text
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  • 2
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    Application of a Laser Interferometer Skin-Friction Meter in Complex Flows (1981)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A nonintrusive skin-friction meter has been found useful for a variety of complex wind-tunnel flows. This meter measures skin friction with a remotely located laser interferometer that monitors the thickness change of a thin oil film. Its accuracy has been proven in a low-speed flat-plate flow. The wind-tunnel flows described here include sub-sonic separated and reattached flow over a rearward-facing step, supersonic flow over a flat plate at high Reynolds numbers, and supersonic three - dimensional vortical flow over the lee of a delta wing at angle of attack. The data-reduction analysis was extended to apply to three-dimensional flows with unknown flow direction, large pressure and shear gradients, and large oil viscosity changes with time. The skin friction measurements were verified, where possible, with results from more conventional techniques and also from theoretical computations.
    Keywords: Lasers and Masers
    Type: NASA/TM-81-207537 , NAS 1.15:207537 , IEEE-Publ-81CH1712-9 , ICIASF 1981; 232-243|International Congress on Instrumentation in Aerospace Simulation Facilities; Sep 30, 1981; Dayton, OH; United States
    Format: application/pdf
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  • 3
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    Features of a reattaching turbulent shear layer subject to an adverse pressure gradient (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Experimental data have been obtained in an incompressible turbulent flow over a rearward-facing step with superimposed adverse pressure gradient. Mean velocities, Reynolds stresses and triple-products measured by a laser Doppler velocimeter are presented for two cases of adverse pressure gradient. Mixing lengths, eddy viscosities, production, convection, turbulent diffusion, and dissipation terms are extracted from the data. These data are compared with various mixing length and eddy-viscosity turbulence models. Numerical calculations incorporating the k-epsilon and the algebraic-stress turbulence models are compared with the data. When determining quantities of engineering interest, the modified algebraic-stress model (ASM) is a significant improvement over the unmodified ASM and the unmodified k-epsilon model
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 82-1029 , Joint Thermophysics, Fluids, Plasma and Heat Transfer Conference; Jun 07, 1982 - Jun 11, 1982; St. Louis, MO
    Format: text
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  • 4
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    Application of a laser interferometer skin-friction meter in complex flows (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The application of a nonintrusive laser-interferometer skin-friction meter, which measures skin friction with a remotely located laser interferometer that monitors the thickness change of a thin oil film, is extended both experimentally and theoretically to several complex wind-tunnel flows. These include two-dimensional seperated and reattached subsonic flows with large pressure and shear gradients, and two and three-dimensional supersonic flows at high Reynolds number, which include variable wall temperatures and cross-flows. In addition, it is found that the instrument can provide an accurate location of the mean reattachment length for separated flows. Results show that levels up to 120 N/sq m, or 40 times higher than previous tests, can be obtained, despite encountering some limits to the method for very high skin-friction levels. It is concluded that these results establish the utility of this instrument for measuring skin friction in a wide variety of flows of interest in aerodynamic testing.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ICIASF ''81; International Congress on Instrumentation in Aerospace Simulation Facilities; Sep 30, 1981; Dayton, OH
    Format: text
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