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ItemMulti-component velocity measurements in turbulent boundary layers( 2015)An experimental investigation of high Reynolds number (Re) turbulent boundary layers is undertaken in this study. The primary focus here is to measure the spanwise and wall-normal velocity components, in addition to the streamwise velocity. This study has been undertaken in an attempt to address the lack of spanwise and wall-normal velocity measurements at high Re, identified in the existing literature. For this purpose, we have utilised a custom dual hot-wire probe that is spatially compact, to reduce the volume occupied by the sensing elements. Measurements at high Re are particularly challenging due to the increased scale separation between the smallest and largest energetic scales. To overcome the challenges of resolving these range of scales, experiments are conducted using a specialised wind tunnel, located at the University of Melbourne, whose 27m length allows a thick boundary layer to be developed. Since Re is equal to the ratio between the largest and smallest scales in the flow, a thicker boundary layer (the largest scale in the flow) equates to a larger permissible physical dimension for sensors to capture the smallest scale, for a fixed Re. We start our study by investigating the effects of finite sensor dimensions on the measured turbulence statistics. In this work, the effects of finite sensor dimensions are simulated numerically using a box filtering process on a three-dimensional velocity field obtained through direct numerical simulation. Two typical dual hot-wire probe configurations, namely V- and X-probes are considered. The simulated results show that X-probes are better suited at measuring the turbulence statistics in a wall-bounded flow compared to V-probes. This is attributed to the wire separation in X-probes, which can be physically configured to be closer than in V-probes. Furthermore, the simulation results suggest that the deviation in the turbulence statistics obtained is a function of utilised sensor dimensions, scaled with viscous units. Therefore, care is taken to match the spatial resolution of the sensor used during the experiments at multiple Re, to avoid contamination from the spatial resolution effects to the Re trends identified. The measured broadband turbulent stresses and cross power spectrogram in the logarithmic region are compared against scaling laws derived using the attached eddy hypothesis. A logarithmic relationship between the streamwise and spanwise turbulence intensities with distance from the wall is observed as predicted by the attached eddy hypothesis. Furthermore, the spanwise, wall-normal and Reynolds shear stress spectrogram obtained are consistent with the notion that the logarithmic region in the wall-bounded flow can be considered to be a collection of self-similar eddies that scale with the wall height; an underlying assumption in the attached eddy hypothesis.