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  • 1980-1984  (7)
  • 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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    An experimental documentation of trailing-edge flows at high Reynolds number (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Experiments documenting attached trailing-edge and near-wake flows at high Reynolds numbers are described. A long, airfoil-like model was tested at subsonic and low transonic Mach numbers, and both symmetrical and asymmetrical flows with pressure gradients upstream of the trailing edge were investigated. Model surface pressures and detailed mean and turbulence flow qualities were measured in the vicinity of the trailing edge and in the near-wake. The data obtained are of sufficient quality and detail to be useful as test cases in assessing turbulence models and calculation methods.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-84375 , A-9376 , NAS 1.15:84375
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    An experimental investigation of the subcritical and supercritical flow about a swept semispan wing (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An experimental investigation of the turbulent, subcritical and supercritical flow over a swept, semispan wing in a solid wall wind tunnel is described. The program was conducted over a range of Mach numbers, Reynolds numbers, and angles of attack to provide a variety of test cases for assessment of wing computer codes and tunnel wall interference effects. Wing flows both without and with three dimensional flow separation are included. Data include mean surface pressures for both the wing and tunnel walls; surface oil flow patterns on the wing; and mean velocity, flow field surveys. The results are given in tabular form and presented graphically to illustrate some of the effects of the test parameters. Comparisons of the wing pressure data with the results from two inviscid wing codes are also shown to assess the importance of viscous flow and tunnel wall effects.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-84367 , A-9359 , NAS 1.15:84367
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  • 4
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    Turbulence Modeling for Unsteady Transonic Flows (1980)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Conditionally sampled, ensemble-averaged velocity measurements, made with a laser velocimeter, were taken in the flowfield over the rear half of an 18% thick circular arc airfoil at zero incidence tested at M = 0.76 and of a Reynolds number based on chord of 11 x 10(exp 6). Data for one cycle of periodic unsteady flow having a reduced frequency bar-f of 0.49 are analyzed. A series of compression waves, which develop in the early stages of the cycle, strengthen and coalesce into a strong shock wave that moves toward the airfoil leading edge. A thick shear layer forms downstream of the shock wave. The kinetic energy and shear stresses increase dramatically, reach a maximum when dissipation and diffusion of the turbulence exceed production, and then decrease substantially. The response time of the turbulence to the changes brought about by the shock-wave passage upstream depends on the shock-wave strength and position in the boundary layer. The cycle completes itself when the shock wave passes the midchord, weakens, and the shear layer collapses. Remarkably good comparisons are found with computations that employ the time-dependent Reynolds averaged form of the Navier-Stokes equations using an algebraic eddy viscosity model, developed for steady flows.
    Keywords: Aerodynamics
    Type: AIAA Paper 79-0071R , AIAA Journal; 18; 5; 489-496|Aerospace Sciences; Jan 15, 1979 - Jan 17, 1979; New Orleans, LA; United States
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  • 5
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    Turbulence Modeling for Unsteady Transonic Flows (1980)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Conditionally sampled, ensemble-averaged velocity measurements, made with a laser velocimeter, were taken in the flowfield over the rear half of an 18% thick circular arc airfoil at zero incidence tested at M = 0.76 and at a Reynolds number based on chord of 11 x 10(exp 6). Data for one cycle of periodic unsteady flow having a reduced frequency f of 0.49 are analyzed. A series of compression waves, which develop in the early stages of the cycle, strengthen and coalesce into a strong shock wave that moves toward the airfoil leading edge. A thick shear layer forms downstream of the shock wave. The kinetic energy and shear stresses increase dramatically, reach a maximum when dissipation and diffusion of the turbulence exceed production, and then decrease substantially. The response lime of the turbulence to the changes brought about by the shock-wave passage upstream depends on the shock-wave strength and position in the boundary layer. The cycle completes itself when the shock wave passes the midchord, weakens, and the shear layer collapses. Remarkably good comparisons are found with computations that employ the time-dependent Reynolds averaged form of the Navier-Stokes equations using an algebraic eddy viscosity model, developed for steady flows.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA/TM-1979-208062 , NAS 1.15:208062 , AIAA Paper 79-0071 , AIAA Journal; 18; 5; 489-496|Aerospace Sciences; Jan 15, 1979 - Jan 17, 1979; New Orleans, LA; United States
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  • 6
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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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  • 7
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    Asymmetric trailing-edge flows at high Reynolds number (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Results from an experimental investigation of asymmetric trailing-edge flows at high Reynolds numbers and subsonic Mach numbers are presented. Measurements include skin friction; surface and flow-field pressures; and mean-velocity, turbulent shear-stress, and turbulent kinetic-energy profiles in the trailing-edge region. Comparisons are made with computed solutions using Reynolds averaged Navier-Stokes and boundary-layer equations; two different turbulence models are used. Two attached flow are considered, one having a moderate adverse pressure gradient and the other a more severe gradient. From the comparisons, an evaluation is made of the predictions for these two pressure-gradient cases. Although the comparisons demonstrate reasonable agreement for the moderate pressure-gradient case, some differences are noted for the severe pressure-gradient case.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 80-1396 , Fluid and Plasma Dynamics Conference; Jul 14, 1980 - Jul 16, 1980; Snowmass, CO
    Format: text
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