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  • 1
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    Flow near a building model in a family of surface layers (1979)
    Elsevier
    Details
    Publication Date: 1979-10-01
    Print ISSN: 0167-6105
    Electronic ISSN: 1872-8189
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Elsevier
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    PAPER CURRENT
  • 2
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    Interaction of free-stream turbulence with screens and grids: a balance between turbulence scales (1982)
    Cambridge University Press
    Details
    Publication Date: 1982-01-01
    Description: Effects of screens and perforated plates (grids) on free-stream turbulence are studied in several test flow conditions. The level, structure and decay of the turbulence generated by such ‘ manipulators ‘ depend in part on their shear-layer instabilities, and can therefore be niodified by inserting additional devices immediately downstream. The performance of screens and some perforated plates is found to depend on the characteristics of the incoming flow such as velocity, turbulence level and spectra. Combinations of perforated plates and screens are found to be very effective flow manipulators. By optimizing the intermanipulator separation and carefully matching the scales between the manipulator pair, the turbulence decay rate downstream of a grid can be quadrupled. © 1982, Archives Europeennes de Sociology. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
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  • 3
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    Effects of axisymmetric contractions on turbulence of various scales (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Digitally acquired and processed results from an experimental investigation of grid generated turbulence of various scales through and downstream of nine matched cubic contour contractions ranging in area ratio from 2 to 36, and in length to inlet diameter ratio from 0.25 to 1.50 are reported. An additional contraction with a fifth order contour was also utilized for studying the shape effect. Thirteen homogeneous and nearly isotropic test flow conditions with a range of turbulence intensities, length scales and Reynolds numbers were generated and used to examine the sensitivity of the contractions to upstream turbulence. The extent to which the turbulence is altered by the contraction depends on the incoming turbulence scales, the total strain experienced by the fluid, as well as the contraction ratio and the strain rate. Varying the turbulence integral scale influences the transverse turbulence components more than the streamwise component. In general, the larger the turbulence scale, the lesser the reduction in the turbulence intensity of the transverse components. Best agreement with rapid distortion theory was obtained for large scale turbulence, where viscous decay over the contraction length was negligible, or when a first order correction for viscous decay was applied to the results.
    Keywords: AERODYNAMICS
    Type: NASA-CR-165136 , R80-1
    Format: application/pdf
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  • 4
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    On the design of contractions and settling chambers for optimal turbulence manipulations in wind tunnels (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The sensitivity of a moderate axisymmetric contraction of turbulence to upstream conditions is parametrically investigated in terms of turbulence intensities and integral length scales. Semi-empirical correlations are derived to characterize the development of turbulence intensities and integral length scales downstream of typical wind-tunnel turbulence manipulators. A new approach is described, permitting wind-tunnel designers to select the characteristic mesh of the turbulence manipulators, a well as the distance from them to the contraction, in order to obtain certain required turbulence characteristics in the test section at the exit of the contraction. The design charts strongly suggest that it may not be possible to achieve small scales and low intensities simultaneously, when using a contraction ratio of nine or larger. The results also confirm that the rapid distortion theory is only valid, with a proper viscous dissipation correction, up to the 'critical point' of a contraction. At that point, the scales of the various components of the velocity are equal and intercomponent transfer from the lateral to the streamwise velocities commences.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 84-0536
    Format: text
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  • 5
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    Experiments on identification and control of inflow disturbances in contracting streams (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Vorticity from all surfaces and isolated objects in the vicinity of the fan intake, including the outside surfaces of the fan housing, were identified as the major sources for disturbances leading to blade passing frequency noise. The previously proposed mechanism based on atmospheric turbulence is refuted. Flow visualization and hot wire techniques were used in three different facilities to document the evolution of various types of disturbances, including the details of the mean flow and turbulence characteristics. The results suggest that special attention must be devoted to the design of the inlet and that geometric modeling may not lead to adequate simulation of the in flight characteristics. While honeycomb type flow manipulators appear to be effective in reducing some of the disturbances, higher pressure drop devices that generate adequate turbulence, for mixing of isolated nonuniformities, may be necessary to suppress the remaining disturbances. The results are also applicable to the design of inlets of open return wind tunnels and similar flow facilities.
    Keywords: AERODYNAMICS
    Type: NASA-CR-169831 , NAS 1.26:169831 , IIT-FHT-R82-3
    Format: application/pdf
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  • 6
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    Interpretation of 2-probe turbulence measurements in an axisymmetric contraction (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Simultaneous measurements of the streamwise and radial velocity components at two points, one on and one off the centerline with variable radial separation, were digitally recorded and processed at several stations along a four to one contraction with controlled upstream turbulence conditions. Various statistical quantities are presented including spectra and coherence functions. The integral L sub ux, L sub um, L sub vx, L sub vm were also estimated and their variation along the contraction is examined.
    Keywords: AERODYNAMICS
    Type: NASA-CR-169832 , NAS 1.26:169832 , IIT-FHT-R83-1
    Format: application/pdf
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  • 7
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    Evaluation of a new concept for reducing free-stream turbulence in wind tunnels (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The feasibility of using a 45 deg-honeycomb for improving the flow quality in wind tunnels was investigated. The results of the experiments indicate that the turbulence levels in a wind tunnel using the 45 deg-honeycomb would be comparable to those obtainable using a conventional honeycomb, i.e., a honeycomb which is positioned normal to the mean flow in the settling chamber. However, this is true only when a 45 deg-screen is mounted immediately downstream of the honeycomb, and when some distance is provided between the trailing edges of the corner turning vanes and the upstream side of the 45 deg-honeycomb. This distance is required for adequate decay of the turning-vane wakes, thereby providing a reasonably uniform mean flow entering the honeycomb. Results demonstrate that this distance should be at least twice the spacing between the turning vanes. Even though the resulting turbulence intensity is the same downstream of both the 45 deg-honeycomb and the conventional honeycomb, there would have to be a significant improvement in the test-section turbulence intensity using the 45 deg-honeycomb to justify the additional expense in fabricating and installing this type of honeycomb.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-3196 , R79-1
    Format: application/pdf
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  • 8
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    Evaluation of a new concept for reducing free-stream turbulence in wind tunnels (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A 45 deg-honeycomb flow manipulator, mounted parallel to the corner turning vanes, was investigated for improving the flow quality in wind tunnels with little or no settling chamber length. This manipulator permits increased turbulence decay distance in comparison to a conventional honeycomb arrangement. The resulting turbulence levels in a wind tunnel using the 45 deg-honeycomb are comparable to those obtained using a conventional honeycomb, but only when a 45 deg-screen is mounted immediately downstream of the honeycomb and when some separation distance between the turning vanes and the 45 deg-honeycomb is provided for adequate decay of the turning vane wakes (at least twice the spacing between the turning vanes).
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: AIAA PAPER 80-0432 , Aerodynamic Testing Conference; Mar 18, 1980 - Mar 20, 1980; Colorado Springs, CO
    Format: text
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