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The turbulent boundary layer is an aspect of fluid flow which dominates the performance of many engineering systems - yet the analytic solution of such flows is intractable for most applications. Our understanding of boundary layers is therefore limited by our ability to simulate and measure them. Tomographic Particle Image Velocimetry (TPIV) is a recently developed technique for direct measurement of fluid velocity within a 3D region. This allows new insight into the topological structure of turbulent boundary layers. Increasing Reynolds Number increases the range of scales at which turbulence exists; a measurement technique must have a larger 'dynamic range' to fully resolve the flow. Tomographic PIV is currently limited in spatial dynamic range (which is also linked to the spatial and temporal resolution) due to a high degree of noise. Results also contain significant bias error. This work proposes a modification of the technique to use more than two exposures in the PIV process, which (for four exposures) is shown to improve random error by a factor of 2 to 7 depending on experimental setup parameters. The dynamic range increases correspondingly and can be doubled again in highly turbulent flows. Bias error is reduced by up to 40%. An alternative reconstruction approach is also presented, based on application of a reduction strategy (elimination of coefficients based on a first guess) to the tomographic weightings matrix Wij. This facilitates a potentially significant increase in computational efficiency. Despite the achieved reduction in error, measurements contain non-zero divergence due to noise and sampling errors. The same problem affects visualisation of topology and coherent fluid structures. Using Projection Onto Convex Sets, a framework for post-processing operators is implemented which includes a divergence minimisation procedure and a scale-limited denoising strategy which is resilient to 'false' vectors contained in the data. Finally, developed techniques are showcased by visualisation of topological information in the inner region of a high Reynolds Number boundary layer (δ+ = 1890, Reθ = 3650). Comments are made on the visible flow structures and tentative conclusions are drawn.

This work examines the relationship between the dynamics of large-scale turbulence structures and the acoustic far-field of high Reynolds number, high-speed jets. Three Mach numbers were examined: 0.9, 1.3 and 2.0. The Mach 1.3 jet was also modified with delta tabs. A novel microphone array / algorithm was developed, tested and then used to locate sources of individual sound waves in space and time. Noise source distributions were compared to and correlated with flow visualization images that were examined with Proper Orthogonal Decomposition (POD). Time and frequency-domain analyses showed the acoustics of Mach 0.9 and 1.3 jets differed from the Mach 2.0 jet due to Mach wave emission in the latter case. Differences associated with turbulence structure scale were observed within the acoustic measurements. The addition of delta tabs led to streamwise vorticity production and the regulation and augmentation of spanwise vorticity. These modifications led to an upstream shift in the noise production regions of the jet and a shift away from the delta tab location. The regions of noise generation coincided with the location where the sides of the mixing layer merge (Mach 0.9, 1.3, 2.0, single-tab, quad-tab jets) or were dramatically altered (bifurcating region of the dual-tab jet). The streamwise vortices were not a strong, direct acoustic source for frequencies on the order of the peak jet radiation at the angle of maximum sound emission. The Mach 1.3 jet was analyzed for periods of noise generation (NG) and relative quiet (RQ) using simultaneously acquired flow and noise source localization data. POD modes were used to reconstruct cross-stream images and a series of crudely phase-locked streamwise images for the two cases. Both image planes showed the lower order POD modes that possess larger scale structures are important to the RQ while the higher order modes with relatively smaller scales dominate the NG. Within the phase-locked NG streamwise images, a series of robust structures form approximately one convective time scale before noise emission and then rapidly disintegrate as fluid is entrained to the jet’s core. The observed NG process bares many similarities to the breakdown of an instability wave.

This thesis presents some results from an experimental study of three-dimensional turbulent tip gap flows in the linear cascade wind tunnel, for two different tip gap clearances (t/c=1.65% and 3.3%). The experiments focus on near-wall flow field measurements for the stationary wall and moving wall, and static pressure measurement on the low end-wall for the stationary wall case. The representative flows were pressure driven, three-dimensional turbulent boundary layers in the linear cascade tunnel for the stationary wall case, and the combination of the pressure driven and shear driven flow for the moving wall case. Several experimental techniques are used in the studies: a three-orthogonal-velocity-component fiber-optic laser Doppler anemometer (3D-LDA) system, surface oil flow visualization, and a scanivalve system for static pressure measurement through pressure ports on the end-wall. From the details of the oil flow visualization pattern on the end-wall, some features of the passage flow, cross flow, and the tip leakage vortex in this cascade flow were captured. Oil flow visualization on the blade surface reveals the reattachment of the tip leakage vortex on the blade surface. The static pressure results on the lower end-wall and mid-span of the blade show huge pressure drop on the lower end-wall from the pressure side to the suction side of the blade and from mid-span to the lower end wall. The end-wall skin friction velocity is calculated from near-wall LDA data and pressure gradient data using the near-wall momentum equation. The statistics of Reynolds stresses and triple products in two-dimensional turbulent boundary layer and three-dimensional turbulent boundary layer was examined using a velocity fluctuation octant analysis in three different coordinates (the wall collateral coordinates, the mid tip gap coordinates, and the local mean flow angle coordinates). The velocity fluctuation octant analysis for the two-dimensional turbulent boundary layer reveals that ejections of the low speed streaks outward from the wall and the sweeps of high speed streaks inward toward the wall are the dominant coherent motions. The octant analysis for the three-dimensional turbulent boundary layer in the tip gap shows that the dominant octant events are partially different from those in the two-dimensional turbulent boundary layer, but ejection and sweep motions are still the dominant coherent motions. For the three-dimensional turbulent boundary layer in the moving wall flow, the near-wall shear flow reinforces the sweep motion to the moving wall and weakens the out-ward ejection motion in the shear flow dominant region. Between the passage flow and the shear flow, is the interaction region of the high speed streaks and the low speed streaks. This is the first time that the coherent structure of the three-dimensional turbulent boundary in the linear cascade tip gap has been studied.

Wind speed data of multi-heights have been examined to investigate the spatial and temporal characteristics of coherent structures in the near neutral marine atmospheric surface layer. With Taylor's hypothesis, the temporal velocity signals have been transformed to spatial fluctuations and then visualize these spatial velocity fluctuations to identify the coherent structures. It has been confirmed that there exist similar coherent structures in the marine atmospheric surface layer to those in laboratory turbulent boundary layer. These similar coherent structures include ejections, sweeps, shear layers, transverse vortices, and combined events of the shear layers and transverse vortices. Besides these similar coherent structures, there exist the plume and downdraft motions in the unstable marine atmospheric surface layer. It has been observed that the streamwise spatial length of the ejections and sweeps is 20-250 m and their mean frequency is of order of 0.01-0.001 /s at mean wind speed of 5-12.6 m/s. Between the region of the upstream ejection and downstream sweep motions an inclined shear layer is often seen. The inclined angle of the shear layer has been observed to vary from 30 to 70 degree with the height and length of the the shear layer. The transverse vortices are seen to exist in every region from the wall up to a height of 45 m and their diameter is up to 40 m. The mean frequency of the shear layers and the transverse vortices is of order of 0.001 /s. In the fully developed stage of the combined event of the shear layer and transverse vortex, the shear layer is generally longer and the diameter of the transverse vortex is larger. The mean frequency of the combined event of the shear layers and the transverse vortices is of order of 0.001 /s. The streamwise spatial length of the plume and downdraft motions is generally from 20 m to 50 m. Analysis indicates that the mean wind speed is a dominant factor in affecting the spatial and temporal characteristics of the coherent structures in the near neutral marine atmospheric surface layer. As the mean wind speed increases, the frequency of the shear related coherent events will increase, while the frequency of the buoyancy related coherent events (plumes and downdrafts) will decrease. The temperature difference between higher level of the surface layer and sea surface is the second main factor in affecting the spatial and temporal characteristics of the coherent structures. As the marine atmospheric surface layer becomes more stable the coherent motions will be suppressed. The effect of the temperature difference on the buoyancy related plume and downdraft motions is more evident than on the other shear related coherent motions.