"Passive scalar concentration and velocity fields of isolated turbulent puffs were examined experimentally using the planar laser Mie scattering and PIV techniques, respectively. Work in WPI laboratories on reacting, fully-modulated jets has indicated significantly reduced flame lengths for compact puffs in comparison with steady and pulsed jets. Of particular interest is the entrainment and mixing of isolated turbulent puffs away from the nozzle. The present experiments were carried out in order to enhance fundamental understanding of the velocity fields associated with isolated, turbulent puffs. Puffs were generated by injecting air through a 5 mm diameter nozzle into a flow chamber with a weak co-flow. The injection time was varied by the use of a fast-response solenoid valve from 20 ms to 161 ms. Puffs with a Reynolds number of 5,000 were examined in the range of 25 - 75 diameters downstream of the nozzle. The results indicate that as the injection volume increases, puffs evolve from a spherical geometry to one with a tail. The distribution of a passive scalar within the examined turbulent puffs is unlike that in turbulent vortex rings. The half-width of radial concentration profile through the puff center decreases as the injection volume increases. On the other hand, the puff length in the axial direction increases with the injection volume. The results from phase-locked PIV measurements indicate that the largest axial mean velocities and the radial velocity fluctuation are within the central portion of the puff and the largest axial velocity fluctuation are typically present above the puff center. The turbulent shear stress profiles within puffs are antisymmetric about the centerline and the maximum magnitude for the smallest injection volume is 2.5 times the steady jet value. The vorticity fields calculated from phase-locked velocity field data indicate the presence of vorticity throughout the puff volume. The ratio of puff volume flow rate to steady jet at the puff center location was largest for the smallest injection volume. The majority of entrainment into the puff occurs below the puff center while the puff cap pushes out into surrounding fluid. In general, the puff characteristics did not reveal an internal structure analogous to that in the turbulent vortex ring."

The master thesis studies the impact of the entropy gradient on the vorticity of ve- locity field, particularly by applying the linear momentum balances. These balances are formulated for Thermo-viscous fluids (later fluids) and Thermo-viscous-elastic ma- terial (later solids) with the other balances (energy, mass, etc.). In order to derive these balances, the Classical continuum mechanics approach is used along with the respec- tive Variational principles. The thesis emphasizes the Variational principles applica- tion representing the modification of the Bateman principle [Bat29] and its comparison with the Classical approach, linked to the L. Crocco work [Cro37], particularly in the case of vorticity generation. It is pointed that by the definition of the dissipative en- tropy sdis a harmony of both approaches can be achieved and that, in the case of an appropriate limit, the direct effect of the entropy gradient on the vorticity of velocity field can be demonstrated. By applying this conclusion the relationship between the change of circulation among a closed curve and released heat on the given geometry is indicated.

This paper presents some mathematical results concerning the measurement of motion of contours. A fundamental problem of motion measurement in general is that the velocity field is not determined uniquely from the changing intensity patterns. Recently Hildreth & Ullman have studied a solution to this problem based on an Extremum Principle [Hildreth (1983), Ullman & Hildreth (1983)]. That is, they formulate the measurement of motion as the computation of the smoothest velocity field consistent with the changing contour. We analyse this Extremum principle and prove that it is closely related to a matching scheme for motion measurement which matches points on the moving contour that have similar tangent vectors. We then derive necessary and sufficient conditions for the principle to yield the correct velocity field. These results have possible implications for the design of computer vision systems, and for the study of human vision.

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Cosmology has become a precision science due to a wealth of new precise data from various astronomical observations. It is therefore important, from a methodological point of view, to develop new statistical and numerical tools to study the Cosmic Microwave Background (CMB) radiation and Large Scale Structure (LSS), in order to test different models of the Universe. This is the main aim of this thesis. The standard inflationary -dominated Cold Dark Matter ( CDM) model is based on the premise that the Universe is statistically isotropic and homogeneous. This premise needs to be rigorously tested observationally. We study the angular correlation function C(θ) of the CMB sky using the WMAP 5-year data, and find that the low-multipoles can be reconstructed from the data outside the sky cut. We apply a Bayesian analysis and find that S1/2 statistic (S1/2 = R [C(θ)]2d cos θ, used by various investigators as a measure of correlations at large angular scales) cannot exclude the predictions of the CDM model. We clarify some issues concerning estimation of correlations on large angular scales and their interpretation. To test for deviation from statistical isotropy, we develop a quadratic maximum likelihood estimator which we apply to simulated Planck maps. We show that the temperature maps from Planck mission should be able to constrain the amplitude of any spherical multipole of a scaleinvariant quadrupole asymmetry at the 1% level (2σ). In addition, polarization maps are also precise enough to provide complimentary constraints. We also develop a method to search for the direction of asymmetry, if any, in Planck maps. B-mode polarisation of the CMB provides another important test of models of the early Universe. Different classes of models, such as single-field inflation, loop quantum cosmology and cosmic strings give speculative but testable predictions. We find that the current ground-based experiments such as BICEP, already provided fairly tight constraints on these models. We investigate how these constraints might be improved with future observations (e.g. Planck, Spider). In addition to the CMB related research, this thesis investigates how peculiar velocity fields can be used to constrain theoretical models of LSS. It has been argued that there are large bulk flows on scales of & 50 Mpc/h. If true, these results are in tension with the predictions of the CDM model. We investigate a possible explanation for this result: the unsubtracted intrinsic dipole on the CMB sky may source this apparent flow, leading to the illusion of the tilted Universe. Under the assumption of a superhorizon isocurvature fluctuation, the constraints on the tilted velocity require that inflation lasts at least 6 e-folds longer (at the 95% confidence interval) than that required to solve the horizon problem. Finally, we investigate Cosmic Mach Number (CMN), which quantifies the ratio between the mean velocity and the velocity dispersion of galaxies. We find that CMN is highly sensitive to the growth of structure on scales (10, 150) Mpc/h, and can therefore be used to test modified gravity models and neutrino masses. With future CMN data, it should be possible to constrain the growth factor of linear perturbation, as well as the sum of the neutrino mass to high accuracy.

Diploma thesis deals with a research of the flow in front of three different automotive vents. The velocity field and intensity of the turbulence was measured in detail, using thermoanemometry. After that the same data was measured with PIV method and validation was performed. The difference between achieved data was investigated. The design among the vents was also investigated, because it’s fundamentally affects the air flow. The purpose of this thesis is to obtain data about the velocity field using two methods and their subsequent use to validate numerical simulations, which will be performed in the future. The diploma thesis also contains the calculation of measurement uncertainty.

The development of a site-specific seismic hazard curve for a soil site requires the incorporation of site effects into the hazard calculation through the use of a site-specific amplification function. This study investigates the effect on the resulting soil hazard curves of different approaches to compute the site-specific amplification function. Amplification functions and their standard deviations can be developed using equivalent linear site response analyses. This study investigates the amplification function predictions of one-dimensional (1D) and two-dimensional (2D) site response analyses. For 1D analysis, one set of analyses are performed using time series (TS) input motions while a second set is performed using random vibration theory (RVT). One-dimensional site response analyses are performed for a shallow and a deep soil site and the results are compared for seismic hazard predictions. The influence of spatial variability introduced through randomization of site shear wave velocity (V[subscript S]) is also investigated. Shear wave velocity profile randomization does not significantly change the predicted amplification functions, except for the RVT analysis near the site period. At these periods, (V[subscript S]) randomization reduces the amplification function predicted by RVT making it more similar to the TS analysis prediction. The surface hazard at a site is dependent on the median amplification factor and its associated standard deviation. Spatial variability and uncertainties in soil properties across a site are often taken into account by modeling multiple 1D profiles in 1D site response analyses. However, this approach assumes that analyzing multiple 1D profiles captures accurately the effects of the true multi-dimensional spatial variability of the soil properties. This study investigates the results of two-dimensional (2D) site response analyses that incorporate spatial variability in the (V[subscript S]) profile through Monte Carlo simulation. Two-dimensional site response analyses are performed for 2D random fields generated with various statistical parameters (i.e. vertical and horizontal correlation distances) to investigate the effect of different levels of spatial variability on surface response across a region of interest (ROI). Two-dimensional site response analyses are performed for a shallow site. Results indicate that horizontal correlation distance has more influence on the analyses results than the vertical correlation distance. As the horizontal correlation distance increases, the median surface response spectrum across the ROI decreases. This reduction in median surface response is more pronounced around the site period. The influence of the vertical correlation distance is more pronounced when the horizontal correlation distance is large. As the vertical correlation distance increases, the median surface response spectrum across the ROI increases, which is more pronounced around the period of the motion. The predictions of 1D and 2D site response analyses modeling the (V[subscript S]) variability are compared. 1D analyses are performed on separately generated 1D (V[subscript S]) profiles (infinite horizontal correlation) and on the (V[subscript S]) profiles across the ROI of each 2D (V[subscript S]) field realization generated for 2D analysis (finite horizontal correlation). The results indicate that both sets of 1D analyses predict lower median response than 2D analyses. The 1D analyses with finite horizontal correlation display comparable levels of variability in the site response, however 1D analyses with infinite horizontal correlation display higher variability. / text

In this study, experimental data was collected in order to create a test case that can be used to validate computational fluid dynamics (CFD) simulations and the individual models used therein for gas turbine combustor applications. In many cases, the CFD results of gas turbine combustors do not correlate well with experimental results. For this reason, there is a requirement to test the simulation method used before CFD can successfully be used for combustor design. This test case encompasses all the features of a gas turbine combustor such as a swirler, primary, secondary and dilution holes as well as cooling rings. Experiments were performed on the same combustor geometry for both non-reacting and reacting flows. The non-reacting flow experiments consisted of stereoscopic particle image velocimetry (PIV) measurements performed at various planes in the three zones of the combustor. Data was collected on planes, both in line with the holes and in between the holes of each zone. For the reacting experiments, the temperatures on the outlet plane were measured using a thermocouple rake, thus a temperature contour plot on the outlet plane was produced. Further, the combustor can was modified with passive inserts, which were tested to determine their influence on the outlet temperature distribution during reacting runs. In this set-up, the outlet velocity profiles were also measured using a Pitot tube during both non-reacting and reacting flows. In addition to the outlet temperature distribution and velocity profiles, images of the flame patterns were captured, which showed the positions of flame tongues, fluctuating flames and steady flames. Carbon burn patterns on the walls of the combustor liner were also captured. From the data collected during the reacting runs, the pattern factor, profile factor, overall pressure loss and pressure loss factor were calculated. The non-reacting experiments performed using the PIV, produced three-dimensional velocity vector fields throughout the combustor. These experiments were performed at various flow rates, which gave an indication of which features of the combustor flow were affected by the flow rate. When comparing the individual PIV images alongside one another, the temporal nature of the combustor flow was also evident. The reacting experiments revealed a hot region of exhaust gas around the outer edge of the exhaust while there was a cooler region in the centre of the outlet flow. The PIV flowfield results revealed the reason for then hot outer ring-like region was due to the path the hot gasses would take. The hot combustor gas from the primary zone diverges outwards in the secondary zone then is further forced to the outside by the dilution recirculation zone. The hot flow then leaves the combustor along the wall while the cooler air from the jets leaves the combustor in the centre. The experiments performed produced a large variety of data that can be used to validate a number of aspects of combustor simulation using CFD. The non-reacting experimental data can be used to validate the turbulence models used and to evaluate how well the flow features were modelled or captured during the non-reacting stage of the combustor simulation process. The typical flow features such as jet penetration depths and the position and size of the recirculation regions are provided for effective comparison. The thermal results presented on the outlet plane of the combustor can be used for comparison with CFD results once combustion is modelled. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Mechanical and Aeronautical Engineering / unrestricted

We estimate the velocity field of the blood flow in a human face from videos. Our approach first performs spatial preprocessing to improve the signal-to-noise ratio (SNR) and the computational efficiency. The discrete Fourier transform (DFT) and a temporal band-pass filter are then applied to extract the frequency corresponding to the subjects heart rate. We propose multiple kernel based k-NN classification for removing the noise positions from the resulting phase and amplitude maps. The 2D blood flow field is then estimated from the relative phase shift between the pixels. We evaluate our approach about segmentation as well as velocity field on real and synthetic face videos. Our method produces the recall and precision as well as a velocity field with an angular error and magnitude error on the average.

This research presents improvements to the velocity field reconstruction process achieved through computer vision. The first improvement of the velocity reconstruction process is the automation of the scanning laser Doppler vibrometer (SLDV) pose procedure. This automated process results in superior estimates of the position and orientation of the SLDV. The second improvement is the refinement of the formulation for reconstruction of the velocity field. The refined formulation permits faster computation, evaluation, and interpretation of the reconstructed structural velocity field. Taken together, these new procedures significantly improve the overall velocity reconstruction process which results in better, unbiased out-of-plane velocity estimates in the presence of noise. The automation of the SLDV pose procedure is achieved through a computer vision model of the SLDV. The SLDV is modeled as a projective camera, i.e. an imager which preserves projectivities. This projective camera model permits the precise association of object features with image features. Specifically, circular features in the object space are seen by the SLDV as ellipses in the image space. In order to extract object points, the bitangents among the circular features are constructed and the bitangent points selected. The accuracy and precision of the object points are improved through the use of a calibrated object whose circular features are measured with a coordinate measuring machine. The corresponding image points are determined by constructing the bitangents among the ellipses and selecting the tangent points. Taken together, these object/image bitangent point sets are a significantly improved data set for previously developed SLDV pose algorithms. Experimental verification of this automated pose procedure includes demonstrated repeatability, independent validation of the estimated pose parameters, and comparison of the estimated poses with previous methods. The refinement of the velocity reconstruction formulation is a direct result of the computer vision viewpoint adapted for this research. By viewing the velocity data as images of the harmonically excited structure's velocity field, analytical techniques developed for holographic interferometry are extended and applied to SLDV velocity images. Specifically, the "absolute" and "relative" fringe-order methods are used to reconstruct the velocity field with the "best" set of bases. Full and partial least squares solutions with experimental velocity data are calculated. Statistical confidence bounds of the regressed velocity coefficients are analyzed and interpreted to reveal accurate out-of-plane, but poor in-plane velocity estimates. Additionally, the reconstruction process is extended to recover the velocity field of a family of surfaces in the neighborhood of the "real" surface. This refinement relaxes the need for the exact experimental geometry. Finally, the velocity reconstruction procedure is reformulated so that independent least squares solutions are obtained for the two in-plane directions and the out-of plane direction. This formulation divides the original least squares problem into three smaller problems which can be analyzed and interpreted separately. These refinements to the velocity reconstruction process significantly improve the out-of-plane velocity solution and interpretation of the regressed velocity parameters. / Ph. D.