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This thesis is concerned with the investigation of boundary layer transition phenomena in relation to turbomachinery flows. The present study involved the experimental investigation of the flow field around flat plates with various leading edge configurations. This study has also included some theoretical predictions using computational fluid dynamics. The experimental investigation involved a variety of free stream environments which have attempted to simulate typical turbomachinery flows. Three flat plate configurations with a sharp, a semi-circular and a C4 leading edge shapes have been employed. The effect of free stream turbulence intensity over a range of free stream Reynolds numbers has been examined. Surface flow visualisation techniques have been applied to a total of 36 different experimental conditions in order to define the transitional characteristics of the boundary layer. This flow visualisation method was found to be appropriate for the large range of test cases involved and especially for the flat plate with the cylindrical leading edge. For the cylindrical leading edge configuration, a separation bubble has been detected in the vicinity of the leading edge, under all tested conditions. Hot-wire investigation of the boundary layer has been undertaken over the flat plate with the C4 leading edge, which has been regarded as the most relevant configuration for turbomachinery applications. This method provided high frequency velocity data which have been analysed in order to obtain information about the spatial distribution of integral parameters of the boundary layer, such as the mean velocity, the turbulence intensity and the skewness and flatness factors. Boundary layer spectra have also been acquired. Statistical analysis of this data has been employed in order to obtain the intermittency distribution. The present results have been found to be in good agreement with existing transition correlations. Calculations of the flow over flat plates with leading edge shapes similar to the experimental configuration have been undertaken using a two-dimensional elliptic Navier-Stokes solver. A solution of the flow field around a semi-circular and an elliptical leading edge has been obtained. Low Reynolds number k-Ɛ modelling has been applied in order to model the transitional characteristics of the boundary layer flow very near the wall. The use of the Nagano-Hishida version of the low-Reynolds number turbulence model led to predictions of an early start and end of transition.

A theoretical and experimental investigation of the character of in turbulent pipe flow has been carried out and some implications for the use of flowmeters considered. An extensive survey of Industrial users of flowmeters has been made, involving the participation of over 70 companies, which provides information about current industrial practice, attitudes and understanding. Axisymmetric perturbations of fully developed turbulent pipe flow been studied using the mixing-length model of turbulence. A linearised theory finds the character of small perturbations, decaying exponentially in the axial direction, in which the tangential and axial motion are independent. A non-linear similarity theory finds the flow field at a particular cross-section of the pipe assuming it to be determined by the specification of the Reynolds number, the pipe's roughness and the swirl number at that cross-section. Laser Doppler Anemometry was used to measure axial and tangential velocities on 4 equidistant cross-sections of a pipe following a double right-angle bend in two perpendicular planes. It was found the tangential velocity had the form of a solid body rotation decayed exponentially. The axial velocity profile after the bend asymmetrical, having the form of a horseshoe which rotated with swirl whilst returning to its fully developed form. Theoretical studies of the effect of the measured axial velocity profiles on the accuracy of electromagnetic and ultrasonic flowmeters presented. It is suggested that the decay of the level of swirl in turbulent flow after a double bend be modelled by the factor exp(-6fz/D) where f is the friction factor in fully developed flow and z/D the dimensionalised axial distance. The accuracy of flowmeters installed at particular locations downstream can then be predicted the appropriate error characteristics of flowmeters are known. Some indications of these characteristics are presented.

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No description available.