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  • Other Sources  (21)
  • 1
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    Turbulence models for compressible boundary layers (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: It is shown that to satisfy the general accepted compressible law of the wall derived from the Van Driest transformation, turbulence modeling coefficients must actually be functions of density gradients. The transformed velocity profiles obtained by using standard turbulence model constants have too small a value of the effective von Karman constant kappa in the log-law region (inner layer). Thus, if the model is otherwise accurate, the wake component is overpredicted and the predicted skin friction is lower than the expected value.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 32; 4; p. 735-740
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  • 2
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    Skin friction and velocity profile family for compressible turbulent boundary layers (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The paper presents a general approach to constructing mean velocity profiles for compressible turbulent boundary layers with isothermal or adiabatic walls. The theory is based on a density-weighted transformation that allows the extension of the incompressible similarity laws of the wall to the compressible regions. The velocity profile family is compared to a range of experimental data, and excellent agreement is obtained. A self-consistent skin friction law, which satisfies the proposed velocity profile family, is derived and compared with the well-known Van Driest II theory for boundary layers in zero pressure gradient. The results are found to be at least as good as those obtained by using the Van Driest II transformation.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 31; 9; p. 1600-1604.
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  • 3
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    A crossed hot-wire technique for complex turbulent flows (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This paper describes a crossed hot-wire technique for the measurement of all components of mean velocity, Reynolds stresses, and triple products in a complex turbulent flow. The accuracy of various assumptions usually implicit in the use of crossed hot-wire anemometers is examined. It is shown that significant errors can result in flow with gradients in mean velocity or Reynolds stress, but that a first-order correction for these errors can be made using available data. It is also shown how corrections can be made for high turbulence levels using available data.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Experiments in Fluids (ISSN 0723-4864); 12; 17-22
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  • 4
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    Structure of three-dimensional turbulent boundary layers (1990)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The changes that occur in the Reynolds-stress-producing motion when a cross-stream pressure gradient is applied to an initially two-dimensional turbulent flow are discussed. Two examples are used: (1) a temporal simulation of a channel flow with crossflow applied by a spanwise pressure gradient for t is greater than 0; and (2) a spatial simulation of the boundary layer on an infinite swept wing. Evidence examined to date suggests that the structural changes in the two cases are similar, but the mechanisms may be significantly different, even if effects peculiar to the viscous wall region are ignored. The results from (2) are provisional, based on too short a time series for accurate statistical averages to be obtained. We treat turbulence 'statistics' (solutions of the Navier-Stokes equations in three space dimensions and time) in the same way as experiments: both have limitations of accuracy but both are acceptable representations of real fluid flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases. 3: Proceedings of the 1990 Summer Program; p 75-84
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  • 5
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    On local approximations of the pressure-strain term in turbulence models (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The results of numerical simulations of turbulent channel flows were used to examine the validity of the local approximation of the pressure-strain term in the Reynolds stress transport equation. Outside of the viscous sublayer the local approximation compares very well with the exact pressure strain. This agreement is due, at least in part, to the high correlation between the rapid pressure and its Laplacian, which suggests that only the near parts of the flow contribute to the rapid pressure at a point. In the viscous sublayer the distance over which the mean shear can be considered constant is comparable to the length scale in the normal direction of the correlations of velocity gradients, leading to failure of the local approximation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases. Proceedings of the 1987 Summer Program; p 159-164
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  • 6
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    Prediction of turbulent shear layers in turbomachines (1974)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The characteristics of turbulent shear layers in turbomachines are compared with the turbulent boundary layers on airfoils. Seven different aspects are examined. The limits of boundary layer theory are investigated. Boundary layer prediction methods are applied to analysis of the flow in turbomachines.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Pennsylvania State Univ. Fluid Mech., Acoustic, and Design of Turbomachinery, Pt. 1; p 251-277
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  • 7
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    Vortex boundary-layer interactions (1986)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The interaction of a turbulent boundary layer (on a flat plate) with a strong artificially-generated longitudinal vortex, which may or may not actually enter the boundary layer, was studied. Experiments, including extensive hot-wire measurements, were completed for the case in which the vortex does enter the boundary layer, and measurements for the somewhat simpler cases in which the boundary layer and vortex remain distinct are now in progress. Contours of total pressure (recently acquired) and of turbulent kinetic energy at various downstream positions are presented to show the overall development of the vortex imbedded in the boundary layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-179982 , NAS 1.26:179982
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  • 8
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    The interaction between a strong longitudinal vortex and a turbulent boundary layer (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper presents the preliminary results of a long-term investigation of the interaction of strong longitudinal vortices with turbulent boundary layers. A pair of trailing vortices is generated by a delta wing, which is mounted ahead of a flat plate so that the trailing vortices merge with the boundary layer on the upper surface of the flat plate, while the non-rolled-up part of the delta-wing wake passes below the plate. This approximates an aircraft wing with a close-coupled canard. The measurements show how the boundary-layer fluid is first subjected to large cross flow and is then transported away from the plate to circulate around the vortex core.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-1071
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  • 9
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    Assessment of closure coefficients for compressible-flow turbulence models (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A critical assessment is made of the closure coefficients used for turbulence length scale in existing models of the transport equation, with reference to the extension of these models to compressible flow. It is shown that to satisfy the compressible 'law of the wall', the model coefficients must actually be functions of density gradients. The magnitude of the errors that result from neglecting this dependence on density varies with the variable used to specify the length scale. Among the models investigated, the k-omega model yields the best performance, although it is not completely free from errors associated with density terms. Models designed to reduce the density-gradient effect to an insignificant level are proposed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-103882 , A-91212 , NAS 1.15:103882
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  • 10
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    Vortex/boundary layer interactions (1989)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Detailed and high quality measurements with hot-wires and pressure probes are presented for two different interactions between a vortex pair with common flow down and a turbulent boundary layer. The interactions studied have larger values of the vortex circulation parameter than those studied previously. The results indicate that the boundary layer under the vortex pair is thinned by lateral divergence and that boundary layer fluid is entrained into the vortex. The effect of the interaction on the vortex core (other than the inviscid effect of the image vortices behind the surface) is small.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-0083
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