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  • 1
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    A mathematically simple turbulence closure model for attached and separated turbulent boundary layers (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 23; 1684-169
    Format: text
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  • 2
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    Transonic separated flow predictions based on a mathematically simple, nonequilibrium turbulence closure model (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A mathematically simple, turbulence closure model designed to treat transonic airfoil flows even with massive separation is described. Numerical solutions of the Reynolds-averaged, Navier-Stokes equations obtained with this closure model are shown to agree well with experiments over a broad range of test conditions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-86826 , NAS 1.15:86826
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  • 3
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    Summary of all cycle II.5 shear and boundary layer measurements, aerodynamics (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The two measurement systems were used to measure mean velocity and velocity, mass flux, and total temperature fluctuations in the turbulent boundary on the fuselage of a KC-135 aircraft. The boundary layer thickness ranged between about 20 and 30 cm for the range of flight Mach numbers from about 0.25 to 0.85 and Reynolds numbers between 3 and 6 x 10 to the 6th power/m. The adaptation of each system for use in airborne applications is discussed. The data obtained from each system are given and compared with each other and they indicate that the two systems represent viable ones for use in future airborne turbulence experiments.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Proc. of the Aero-Optics Symp. on Electromagnetic Wave Propagation from Aircraft; p 459-464
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  • 4
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    Unsteady density and velocity measurements in the 6 foot x 6 foot wind tunnel (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The methods used and the results obtained in four aero-optic tests are summarized. It is concluded that the rather large values of density fluctuation appear to be the result of much higher Mach number than freestream and the violent turbulence in the flow as it separates from the turret. A representative comparison of fairing on-fairing off rms density fluctuation indicates essentially no effect at M = 0.62 and a small effect at M = 0.95. These data indicate that some slight improvement in optical quality can be expected with the addition of a fairing, although at M = 0.62 its effect would be nil. Fairings are very useful in controlling pressure loads on turrets, but will not have first order effects on optical quality. Scale sizes increase dramatically with increasing azimuth angle for a reprensentative condition. Since both scale sizes and fluctuation levels increase (total turbulence path length also increases) with azimuth angle, substantial optical degradation might be expected. For shorter wave lengths, large degradations occur.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Proc. of the Aero-Optics Symp. on Electromagnetic Wave Propagation from Aircraft; p 153-181
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  • 5
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    A generalized expression for lag-time in the gas-phase permeation of hollow tubes (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A generalized expression for the nonsteady-state parameter, lag-time, has been obtained from Fick's second law for gas-phase transport through hollow, cylindrical membranes. This generalized expression is simplified for three limiting cases of practical interest: (1) diffusion controlled transport, (2) phase boundary reaction control at the inlet surface, and (3) phase boundary reaction control at the outlet surface. In all three cases the lag-time expressions were found to be inversely proportional only to the diffusion coefficient and functionally dependent on the membrane radii. Finally, the lag-time expressions were applied to experimentally obtained lag-time data for alpha-phase titanium and alpha-phase iron.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science; 6A; Feb. 197
    Format: text
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  • 6
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    A laser Doppler velocimeter approach for near-wall three-dimensional turbulence measurements (1990)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A near-wall laser Doppler velocimeter approach is described that relies on a beam-turning probe which makes possible the direct measurement of the crossflow velocity at a grazing incident and the placement of optical components close to the flow region of interest regardless of test facility size. Other important elements of the approach are the use of digital frequency processing, an optically smooth measurement surface, and observation of the sensing volume at 90 degrees. The combination was found to dramatically reduce noise-in-signal effects caused by surface light scattering. Turbulent boundary-layer data to within 20 microns (y(sup+) approximately equal to 1) of the surface are presented which illustrate the potential of the approach.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-102841 , A-90207 , NAS 1.15:102841 , International Symposium on Application of Laser Techniques in Fluid Mechanics; Jul 09, 1990 - Jul 12, 1990; Lisbon; Portugal
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  • 7
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    A new turbulence closure model for boundary layer flows with strong adverse pressure gradients and separation (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A new turbulence closure model designed specifically to treat two-dimensional, turbulent boundary layers with strong adverse pressure gradients and attendant separation, is presented. The influence of history effects are modeled by using an ordinary differential equation (ODE) derived from the turbulence kinetic-energy equation, to describe the streamwise development of the maximum Reynolds shear stress in conjunction with an assumed eddy-viscosity distribution which has as its velocity scale the maximum Reynolds shear stress. In the outer part of the boundary layer, the eddy viscosity is treated as a free parameter which is adjusted in order to satisfy the ODE for the maximum shear stress. Because of this, the model s not simply an eddy-viscosity model, but contains features of a Reynolds-stress model. Comparisons with experiments are presented which clearly show the proposed model to be superior to the Cebeci-Smith model in treating strongly retarded and separated flows. In contrast to two-equation, eddy-viscosity models, it requires only slightly more computational effort than simple models like the Cebeci-Smith model.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 84-0175
    Format: text
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  • 8
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    Boundary Conditions for Unsteady Compressible Flows (1994)
    In:  CASI
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    Publication Date: 2019-08-17
    Description: This paper explores solutions to the spherically symmetric Euler equations. Motivated by the work of Hagstrom and Hariharan and Geer and Pope, we modeled the effect of a pulsating sphere in a compressible medium. The literature available on this suggests that an accurate numerical solution requires artificial boundary conditions which simulate the propagation of nonlinear waves in open domains. Until recently, the boundary conditions available were in general linear and based on nonreflection. Exceptions to this are the nonlinear nonreflective conditions of Thompson, and the nonlinear reflective conditions of Hagstrom and Hariharan. The former are based on the rate of change of the incoming characteristics; the latter rely on asymptotic analysis and the method of characteristics and account for the coupling of incoming and outgoing characteristics. Furthermore, Hagstrom and Hariharan have shown that, in a test situation in which the flow would reach a steady state over a long time, Thompson's method could lead to an incorrect steady state. The current study considers periodic flows and includes all possible types and techniques of boundary conditions. The technique recommended by Hagstrom and Hariharan proved superior to all others considered and matched the results of asymptotic methods that are valid for low subsonic Mach numbers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106737 , ICOMP-94-22 , E-9138 , NAS 1.15:106737
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  • 9
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    Separated skin-friction measurements - Source of error: An assessment and elimination (1980)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Potential sources of error in the use of heated surface gages for separated-skin-friction measurement are studied. Emphasis is placed on the interpretation of local skin-friction measurements in two- and three-dimensional separated turbulent-shear flows before they are used to test the validity of current and proposed computer codes.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 80-1409 , Fluid and Plasma Dynamics Conference; Jul 14, 1980 - Jul 16, 1980; Snowmass, CO
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  • 10
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    Near-wall, three-dimensional turbulence measurements: A challenge for laser velocimetry (1989)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A new laser velocimeter approach is presented, which has distinct advantages in near-wall, two- and three-dimensional turbulence measurement applications. The approach does require placing a probe into the flow; but in return, there are some important benefits, such as, the direct measurement of the crossflow velocity, w, at a grazing incidence, and the ability to size optical components for the scale of the flow rather than the size of the facility. Promising resuls were obtained with this approach for a two-dimensional turbulent boundary layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-102252 , A-89261 , NAS 1.15:102252 , International Congress on Applications of Laser and Electro-Optics; Oct 15, 1989 - Oct 20, 1989; Orlando, FL; United States
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