No description available.

No description available.

No description available.

The objective of this thesis research is to further the understanding of turbulent diffusion by experimentally studying the turbulent diffusion of a plume of dye released in uniformly sheared flow generated in a water tunnel. The flow studied was nearly homogeneous but strongly anisotropic and had a turbulent Reynolds number of 150. Maps of the turbulent velocity and dye concentration were measured simultaneously using stereoscopic particle image velocimetry and planar laser-induced fluorescence. A thorough analysis of the planar laser-induced fluorescence technique was performed; several previously unconsidered sources of error were identified and corrections were proposed. The measured evolutions of the mixed velocity-concentration statistics of the plume were compared with previous studies. The turbulent scalar flux vector was related to the mean concentration gradient through a first-order gradient transport model and, for the first time in an experimental flow, all components of the turbulent diffusivity tensor were measured directly. The turbulent diffusivity tensor was found to be highly anisotropic and its streamwise component appeared to be counter-gradient. The relative diffusion of the plume was also investigated and the evolution of the mean square particle separation was found to be consistent with Richardson-Obukhov scaling, with a value of Richardson's constant equal to 0.35. The fine structure of the concentration field and the mixed velocity-concentration statistics were also documented. Because of the high level of intermittency of the present plume, the scalar probability density function was strongly non-Gaussian and the conditional expectations of the velocity components and the scalar dissipation, conditioned upon the scalar value, were distinctly non-linear. Lastly, the role of coherent structures on scalar diffusion was investigated and a conditional eddy analysis demonstrated that hairpin vortices were associated closely with large scalar flux events.

A study of the squish-jet design concept in spark ignition engines, with central ignition, was conducted in a constant volume chamber. The effects of jet size, jet number and jet orientation in generating turbulence and jet enhanced turbulent combustion were investigated. Three sets of configurations with three port sizes were used in this study. The research was carried out in three stages: 1.Qualitative information was obtained from flow visualization experiments via schlieren photography at 1000 frames per second. The flow medium was air. A sequence of frames at specific time intervals were selected to study the results from the respective configurations and jet sizes. The swirling nature of the flow is vivid in the offset arrangement. 2.Pre-ignition pressure and combustion pressure traces were measured with a piezoelectric pressure transducer from which characterising parameters such as maximum pressure, ignition advance and mass burn rate were analysed. Mass fraction curves were calculated using the simple model of fractional pressure rise. A maximum pressure increase of 66% over the reference quiescent combustion case, and combustion duration reduction of 77% were obtained for the offset arrangement with 2 mm diameter port. Comparisons of the times required for 10%, 50% and 90% mass burned are identified and confirmed that it took the 2 mm jet the shortest time to burn 90% of the mixture in the chamber. 3.Two-component velocity measurements were made using an LDV system. Measurements were taken in the central vertical plane of the chamber at specified locations. The data collected were window ensemble- averaged for the mean and fluctuating velocities over a number of cycles. Data intermittency and low data rate precluded, however, cycle-by-cycle analysis. Mean tangential velocities were calculated for each case and the data were used to construct a movie of the tangential velocity as a function of time, suitable for quantitative flow visualization. The vortical nature of the flow was recorded, the distribution being neither solid body rotation nor free vortex, but some complex fluid motion. The jet scale and orientation influence the in generation of turbulence flow field in the chamber, affecting the rate of combustion and the ensuing maximum pressure rise. The offset jet arrangement gives the best results, whereas radially opposed jets have a reduced effect. Increasing the number of jets in opposed arrangement does not enhance turbulent flow. Turbulent flow in the spark region during the onset of ignition was found to be important. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The structure of a stable smooth wall zero pressure gradient turbulent boundary layer is investigated experimentally in order to determine the dominant outer region structure and to develop a hypothetical generalized boundary layer flow model. Three hot wire configurations, two vertically separated X-wires and a leading straight wire, a horizontal rake of 5 straight wires, and a vertical rake of 5 straight wires were used in the experiments, conducted at Reɵ = 8200. The basis for data reduction procedures came from crosscorrelations and the Variable Interval Time Average (VITA) technique. Three structure types are reported in the literature to be important: streaks and counter rotating streamwise vorticity, wall scaled hairpins or ring vortices, and large scale (0(ઠ)) bulges. A simple pictorial model consisting of three Reɵ dependent interdeveloping stages, which integrate all three structure types, is presented and discussed in relation to the literature and experiments performed. The rake data indicate that the positive ([formula omitted]u/[formula omitted]t) VITA detected velocity front has a scale much larger than that of the wall scaled eddies which typically have a scale of 100-300 y[formula omitted], and that this velocity front exhibits characteristics that are consistent with the trailing velocity front described in the model. The general convection velocity from basic crosscorrelations and the convection velocity of the positive VITA detected velocity front both had values 90-100% of the local mean velocity over most of the boundary layer. Evidence of small scale structure concentration on the downstream edge of the trailing velocity front is presented. A new method used to determine the average structure inclination angle associated with the trailing velocity front is presented and demonstrates that the generalized structure inclination angle, calculated from basic crosscorrelations between vertically separated sensors, does not indicate structure shape, but is associated with the bulk flow associated with the structure. The new method appears to give results that are consistent with flow visualization and more accurately estimates the inclination angle associated with the most dominant feature of the outer flow, the positive VITA velocity front. Although the model presented is somewhat crude and further development and refinement are required, the model appears to agree with most data in the literature, as well as the present experimental results. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Measurement of turbulent fluctuations of wind temperature and humidity to determine the momentum, sensible heat and latent heat surface fluxes were made in Bimini Island, in April - May 1971 over Grand Bahamas Banks. The temperature spectralshape and WT cospectral shape showed strong time dependency. The temperature and humidity turbulent fluxes were dissimilar some of the time as in the case of B.O.M.E.X. This dissimilarity and time dependency of the spectra and cospectra depend on the structure of the vertical profile of deeper layers which is determined by the evolution of the tropical inversion layer. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

An instrument was developed to measure the static pressure fluctuations within the turbulent flow of the atmospheric boundary layer. This instrument was used to measure some of the properties of pressure fluctuations over a flat boundary and over water waves and has provided the first reliable pressure data within a turbulent boundary layer. For all observations over a flat boundary the root-mean-square pressure produced by the boundary layer turbulence was about 2.6 times the mean stress. The spectra had a power law behaviour with a mean slope of -1.7 for scales above the peak of the vertical velocity spectrum. Pressure fluctuations were approximately spherical in shape, and propagated downstream at a rate equal to the 'local' mean wind. Above the boundary, the large scale pressure fluctuations were approximately in phase with the downstream velocity fluctuations; at small scales there was a large phase difference (≃135°). These phase differences were interpreted to be the result of the large pressure producing scales interacting with the earth's surface, while the small scales were 'free' of the surface. Pressure forces resulted in an energy flux out of the downstream velocity fluctuations of about 0.45 of the total energy source for the turbulence within the band of 0.05 < kz < 20. The pressure term in the net energy budget was found to be about 1/10 of the energy feeding term. Pressure measurements near wind generated waves showed a large spectral hump at the wave frequencies. The amplitude of this hump increased, and its vertical rate of decay decreased, as the mean wind speed increased. The phase difference between pressure and waves during active generation was found to be about 135°, pressure lagging waves. This did not change vertically. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The work carried out for this thesis forms part of a program to study air-sea interaction processes which has been under way at the Institute of Oceanography of the University of British Columbia during the past four years. Measurements of the spectra of fluctuations of the velocity, temperature, and quantities related to the total rate of dissipation of kinetic energy were made in the air just above the sea surface, Particular attention was focused on the high wave number region of the spectra for which there are predictions for the spectral forms from the theory of turbulence. The measurements of the velocity fluctuations were made with hot-wire anemometers of the constant current type. The temperature fluctuations were measured with a platinum resistance thermometer consisting of a platinum wire 2.5 microns in diameter and about 2mm long. The fluctuations of the quantities related to the dissipation rate were obtained from the velocity fluctuations using an analog computer to perform the necessary operations. The spectral analyses were performed by analog techniques. The measured velocity spectra, when normalized in the required was showed excellent agreement with the measurements of other investigators who worked in different flow fields. The experimental evidence now available provides very strong support for the Kolmogoroff contention that there exists a universal form to the high wave number part of the spectrum of high Reynolds number turbulence. This universal form might be expected to be affected by the observed intermittency of the turbulence. However, such effects, if they exist, must be smaller than the observed experimental scatter of 10 to 15%. The spectrum of the temperature fluctuations shows good agreement with the predictions, obtained from arguments similar to the Kolmogoroff ones for the velocity spectrum, over the rather limited wave number range which it was possible to investigate. The wave number spectra of the fluctuations of the quantities related to the dissipation rate agree with the predictions of Novikov and Stewart (19 64) that these spectra should have a power law form in the inertial subrange with the power of the wave number lying between 0 and -1. One of the requirements for the validity of their prediction is that the flatness factor for the velocity fluctuations and their spatial derivatives should be very much larger than the flatness factor for a Gaussian random variable. The few measurements which were made of flatness factors showed that this requirement is very well satisfied. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An acoustic Doppler current profiler (ADCP) has been tried and found suitable for taking profiles of the time-mean three-dimensional velocity, vertical shear. Reynolds stress and turbulent kinetic energy (TKE) density in a coastal tidal channel. The velocity profiles have been used to reveal the existence of a log-layer. The data collected with the ADCP have been combined with fine- and microstructure data collected with a moored instrument (TAMI) to examine the TKE budget and turbulence characteristics in tidal flows. The ADCP was rigidly mounted to the bottom of the channel and the instrument was set to rapidly collect samples of along-beam velocities. In the derivation of the mean flow vector and the second-order turbulent moments, one must assume that the mean flow and turbulence statistics are homogeneous over the distance separating beam pairs. A comparison of the estimated mean velocity against the “error” velocity provides an explicit test for the assumption of homogeneity of the mean flow. The number of horizontal velocity estimates that pass a simple test for homogeneity increases rapidly with increasing averaging distance, exceeding 95% for distances longer than 55 beam separations. The Reynolds stress and TKE density are estimated from the variances of the along-beam velocities. Doppler noise causes a systematic bias in the estimates of the TKE density but not in the Reynolds stress. With increasing TKE density, the statistical uncertainty of the Reynolds stress estimates increases, whereas the relative uncertainty decreases. The spectra of the Reynolds stress and the TKE density are usually resolved; velocity fluctuations with periods longer than 20 minutes contribute little to the estimates. Stratification in the channel varies with the strength of the tidal flow and is weak below mid- depth. The ADCP measurements provide clear examples of secondary circulation, intense up/down- welling events, shear reversals, and transverse velocity shear. Profiles of the streamwise velocity are fitted to a logarithmic form with 1% accuracy up to a height, defined as the height of the log-layer, that varies tidally and reaches 20 m above the bottom during peak flows of 1 m s ⁻¹. The height is well predicted by 0.04u*/ω, where u * is the friction velocity and ω is the angular frequency of the dominant tidal constituent. The mean non-dimensional shear, [special characters omitted],is within 1% of unity at the 95% level of confidence inside the log-layer. Estimates of the rates of the TKE production and dissipation, eddy viscosity and diffusivity coefficients and mixing length, are derived by combining measurements with the ADCP and TAMI located at mid-depth. Near the bottom (z = 3.6 m), the production rate is 100 times larger than all other measurable terms in the TKE equation. Hence, the rate of production of TKE must be balanced by dissipation. The observed rate of production is proportional to the rate of dissipation calculated using the observed TKE density and mixing length, following the closure scheme of Mellor and Yamada (1974). This proportionality holds for the entire 3 decades of the observed variations in the rate of TKE production. At mid-depth, the eddy diffusivity of density and heat, deduced from microstructure measurements, agrees with the eddy viscosity derived from measurements with the ADCP. The scaling of the log-layer height with tidal frequency in the channel is comparable to the scaling with Coriolis parameter for the log-layer in steady planetary boundary layer. However, some results are inconsistent with those from boundary layers over horizontal homogeneous bottoms. The Reynolds stress is not constant within the log-layer, and its magnitude at 3.6 m above the bottom is 3 times smaller than the shear velocity squared [special characters omitted] derived from log-layer fitting. The peak of the non-dimensional spectrum for the Reynolds stress, when compared to measurements from atmospheric boundary layer, is shifted to higher wavenumbers by a factor of 2.5. One possible explanation for these discrepancies is the influence of horizontal inhomogeneity caused by bed forms. / Graduate