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  • 1
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    Calculations of unsteady turbulent boundary layers with flow reversal (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The results are presented of a series of computational experiments aimed at studying the characteristics of time-dependent turbulent boundary layers with embedded reversed-flow regions. A calculation method developed earlier was extended to boundary layers with reversed flows for this purpose. The calculations were performed for an idealized family of external velocity distributions, and covered a range of degrees of unsteadiness. The results confirmed those of previous studies in demonstrating that the point of flow reversal is nonsingular in a time-dependent boundary layer. A singularity was observed to develop downstream of reversal, under certain conditions, accompanied by the breakdown of the boundary-layer approximations. A tentative hypothesis was advanced in an attempt to predict the appearance of the singularity, and is shown to be consistent with the calculated results.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-2546
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Unsteady turbulent boundary layers with flow reversal (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A theoretical study is carried out to search for the appearance of a singularity in a family of time-dependent turbulent boundary layers with embedded reverse-flow regions and determine the conditions necessary for its appearance. Further insight is gained into the development of unsteady turbulent boundary layers. The calculations performed for a family of prescribed external velocity distributions in which the relative importance of the effects of time-dependence, compared to those of spatial diffusion, are controlled by a given parameter. The conditions necessary for the appearance of a singularity appears to involve the existence of an appropriate relationship between the dominant velocities in the reversed-flow region and the rate of forward movement of the flow reversal point. The results support the hypothesis that a singularity will exist in the flow if and only if the typical reversed-flow velocities exceed the rate of penetration of the reversed flow into the oncoming boundary layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Unsteady aerodynamics; Mar 18, 1975 - Mar 20, 1975; Tucson, AZ
    Format: text
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    NASA TECHNICAL REPORTS
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