Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The behaviour of turbulent boundary layers above complex terrain is of interest from several viewpoints. From an engineering viewpoint, much of the interest centres on the velocity increase, or 'speedup', that occurs above the crests of such surfaces, while meteorologists are interested in the effects of such surfaces for inclusion in large scale numerical weather prediction models. In this study the flow of a turbulent boundary layer over complex terrain is considered using both experimental and numerical methods.;In the experimental study flow and surface pressure measurements were made for both sinusoidal waves and complex surfaces containing a range of length scales. The measurements suggest that, once established, the flow in the outer region of the boundary layer is independent of position with respect to the underlying surface. Within this region the areally averaged horizontal velocity and Reynolds stress profiles exhibit similar relationships as those observed above flat surfaces. Furthermore it is shown that the observed increases in the Reynolds stress component {dollar}\overline{lcub}u\sp\prime w\sp\prime{rcub}{dollar} are consistent with the form drag calculated to be acting on the underlying surface.;Using results from a linear numerical model of turbulent boundary layer flow over topography a spectral parameterization for the form drag was developed. This parameterization uses a linear combination of the terrain spectrum and a defined pressure transfer function to obtain the form drag acting on a section of complex terrain, and has been shown to give values that are in excellent agreement with those calculated using the numerical model.;A comparison of the experimentally measured speedup values with those calculated using both the linear numerical model and a typical engineering design method showed that the experimental and numerical results were in good agreement in most cases. Conversely it was found that speedup values estimated using the design code method were generally in excess of the measured values.;Finally a comparison of the experimental form drag values with those calculated using the linear numerical model showed that there were large discrepancies between the two sets of results. Consideration of other numerical studies suggests that the underprediction of the form drag is a feature of all numerical models. Given the sensitivity of the calculated form drag to the turbulence closure used in the numerical model, this suggests that even the higher order turbulence closures currently being used are insufficient to completely model the turbulence fields in such flows.



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