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Title: The response of separated turbulent boundary layers to the upstream presence of small two-dimensional surface discontinuities
Author: Alhusein, Mahmoud Abdel-Rahim
Awarding Body: University of Leicester
Current Institution: University of Leicester
Date of Award: 1988
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The influence of the upstream presence of small two-dimensional surface discontinuities on the downstream characteristics of the separated turbulent boundary-layer flow in which they are immersed was studied both experimentally and by means of an appropriate boundary layer prediction model. In the experimental part, flow separation induced by an adverse pressure gradient was established first over a smooth surface. Different sizes of surface discontinuities of mainly square cross-section have been spanned across the surface upstream at different positions. Measurements were made at various stations of mean velocity profiles, wall skin friction, and longitudinal normal stress component distributions both with and without the surface discontinuities being present. Boundary layer integral parameters and drag coefficients were deduced from the measured velocity profiles. The pulsed-wire anemometer was used for the bulk of these measurements. Pitot and Preston tubes were also used in regions where the flow was less unsteady. The lag-entrainment integral prediction method was employed to determine two-dimensional separated flow characteristics. The method is used in an inverse mode in which the displacement thickness is specified and the pressure distribution is predicted together with other boundary layer integral parameters. The presence of the surface discontinuities was modelled and methods for continuing the boundary layer prediction process across and then downstream of these discontinuities were developed. Satisfactory agreement with the experimental data was obtained which suggests that the developed technique provides an adequate computation procedure for this application. Taking into account both the experimental results and the computer predictions, the investigation reveals that the presence of small surface discontinuities upstream does not greatly affect the separation process downstream, either in its location or its flow characteristics. However, when this surface discontinuity height is larger than the height of the boundary layer logarithmic region the downstream separation point is moved to the location of the surface discontinuity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available