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An image processing approach to turbulence studies has been developed. The approach employs a structure tracking technique to quantify the movement of coherent, large-scale turbulent structures. The 'structure tracking' technique has been applied to the shear layer of a low speed jet issuing into a low speed crossflow. A study of the characteristics of the turbulent flow within this region involved comparative measurements with hot-wire anemometry measurements within the same flow regime and fractal analysis of the flow visualisation images used by the tracking routine. Fractal analysis was applied to flow visualisation images to educe a range of length scales made apparent by the flow visualisation equipment The results obtained with the structure tracking technique included the instantaneous velocity of the structures and a measure of their length scales. The instantaneous velocity measurements were used to calculate a turbulence characteristic associated with the structures. Further analysis revealed subsets of this turbulence characteristic involving the variation in average velocity of individual structures as well as variations in the instantaneous velocity of individual structures. Where possible, the results of the structure tracking technique were compared to those achieved by hot wire anemometry and good correspondence was found between the mean flow characteristics measured by both techniques. The results of the two techniques began to diverge in the regions of the flow where conventional hot-wire anemometry was unable to discriminate between the flow associated with the jet and that associated with the crossflow. In such regions, time-averaged hot-wire anemometry produced results which combined the measurements in both flow regimes and therefore attenuated any characteristics of the jet which were significantly different from those of the crossflow. In the same flow regions the structure tracking technique was able to measure those characteristics specifically associated with the jet, producing results, which reflected the behaviour of the jet more accurately.

Understanding the formation and growth of aerosols is important to a better understanding of a diverse range of problems. The identification of key parameters affecting aerosol behaviour is discussed, and a number of approaches for predicting this behaviour are developed in this thesis. Models appropriate to a wide range of industrial processes are used. Turbulent and laminar flow scenarios are considered, and an assessment is made of the likely differences in system behaviour according to whether nucleation occurs by a predominantly homogeneous, binary or ion-induced mechanism. A number of techniques for predicting aerosol behaviour are compared, ranging from the rigorous to more elementary approaches. It is shown that the simpler techniques are able to demonstrate many of the most important features of aerosol behaviour, whilst allowing the isolation of the parameters which influence this behaviour. This thesis presents methods which are capable of rapidly characterising the growth and formation behaviour of an aerosol system, and in doing so has identified many of the parameters which control this behaviour.

The major challenge associated with saving energy in the pumping stations of the fluid transportation in the pipeline networks, especially the crude oil transportation for long-distance is drag forces. In other words, this grossly increases the drag form force and friction losses making fluids transport inside pipeline taken a long time to pass, that increases energy consumption and costs. Therefore, the effective solution to overcome these problems is added drag reduction materials (DRMs) with the main fluid using the drag reduction technique (DR). One of the most important drag reduction technique to enhance flow in the pipeline is an active drag reduction using DRMs. Where the DRMs can reduce drag forces in relatively small amounts part per million (ppm), as well as environment friendly. Thereby, the drag reduction enhancement is highly important in terms of fluid transportation in the many industrial applications. An experimental and mathematical study have been performed in the fully development flow to measure fluid characteristics and to evaluate %DR using various DRMs: polymers, surfactants, and nanoparticles in pipeline network. The active drag reduction experiments have been conducted in the rotational disk apparatus (RDA) and in the closed-loop recirculation system (CLRS) using different solutions of DRMs: individual, binary, and triple at different Reynolds numbers (Re) and at different concentrations. The morphological tests have been done employing XDR, TEM and SEM techniques. Mathematical model was presented to validate the experimental results using the statistic softwareV6.2. The results have been displayed with complete explanation, analysis, and conclusions. The results show that the %DR increases with increasing the velocity (Re) and concentration for the most of DRMs solutions. Also, the results confirm that the use of nanoparticle in complex solutions is more effective than using nanoparticle individually within the same work condition. further, the new complex solutions were formed in a manner that can contribute significantly to increase drag reduction performance and enhance shear resistance of the DRMs. Finally, all microscopy techniques confirm the fact that complex solutions were effectively formed and homogenized within the main fluid.

Many engineering processes involve a gas and a liquid or two immiscible liquids in turbulent flow. The turbulent flows present in two-phase systems will cause the bubbles or drops of a dispersion to undergo breakup and coalescence, and the resulting changes in the dispersion may significantly affect the engineering process under consideration. For this reason, many researchers have studied breakup and coalescence in turbulent two phase flows. Models that can be used to simulate changes in a dispersion over time have been proposed, but these models contain constants that change with experimental conditions and empirical equations that can only be considered valid for certain experimental setups. The goal of this study was to develop general models that could be used to predict changes in bubble or drop size distributions over time for turbulent flows in agitated vessels and pipes. Computer programs were written to reproduce the results of three agitated vessel studies. These programs used existing population balance models to approximate the changes in a dispersion over time measured in previous experiments. A new model for breakup in agitated vessels was then developed and verified with existing experimental data. A new model for coalescence in agitated vessels was also developed and verified with existing experimental data. Both of these models are based on theory and are more readily extendible than previous breakup and coalescence models. The work for agitated vessels was then extended to turbulent two-phase pipe flow. Since there was only a limited amount of experimental data available for breakup and coalescence in pipes, the model for turbulent pipe flow could not be verified. / Master of Science

<p> The pressure gradients for sphere trains in 1 in. and 2 in. pipes have been measured with water flowing past the stationary spheres at Reynolds numbers (based on pipe diameter) from to 4 - 105 , and sphere/pipe diameter ratios ranging from 0.486 - 0.84. Two dimensionless pressure ratios have been derived so that the experimental results obtained can be generalised to any pipe diameter with the above constraints on Reynolds number and diameter ratio. Drag coefficients have also been calculated from pressure drop measurements for the 0.84 diam. ratio spheres in· 1 in. pipe. These have been compared with McNoun's drag coefficient. </p> <p> The application of the results to predict pressure gradients for sphere trains in any pipe diameter has been illustrated. </p> / Thesis / Master of Engineering (MEngr)

Due to their efficient heat and mass transfer potential, impinging jets have received attention in various applications. Heat transfer and flow characteristics of rectangular turbulent impinging jets issued from a 24:1 aspect ratio and 24:1 contraction ratio nozzle were investigated experimentally and numerically. In the heat transfer measurements; a thin stainless-steel foil was utilized to obtain iso-flux boundary conditions on the impingement surface. The target plate was free to translate in the lateral direction and the heat transfer distributions were determined at 0 ≤ x/W ≤ 20 with the micro-thermocouples placed underneath the foil. The measurements were conducted for Re(j) = 8900 − 48600 at nozzle-to-target spacing of 0.5 ≤ H/W ≤ 12.0. Both semi and fully confined jets were investigated. Heat transfer coefficients at Re(j) = 28100, 36800, 45600 and H/W = 4.0 were determined by using adiabatic-wall temperatures and the distributions were compared with those of the wall shear stress. Off-center peaks were observed at high Re(j) and low H/W. Since the wall distributions are susceptible to nozzle-exit conditions, velocity and turbulence profiles at the nozzle-exit were measured for the velocity range of interest. Additionally, near-wall mean velocity and turbulence profiles were determined at Re(j) = 21500 and 36800 at H/W = 4.0 to have a better understanding of the secondary peaks in the wall distributions. Numerical computations were performed by using several different turbulence models (k − ω, k − ε, V 2F and Reynolds stress models). In wall-bounded turbulent flows, near-wall modeling is crucial. Therefore, the turbulence models eliminating wall functions such as the k − ω and V 2F models may be superior for modeling impingement flows. The numerical results showed reasonable agreement with the experimental data for local heat transfer and skin friction coefficient distributions. The occurrence of the secondary peaks was predicted by the k − ω and V 2F models, and for a few cases with the low-Re-k − ε models. Near-wall measurements along with the computed profiles were used to describe the “secondary peak” phenomena. It was shown that the increase in turbulence production in the wall-streamwise direction enhances turbulent momentum and heat transport in the wall-normal direction which lead to secondary peaks in the wall distributions. The possibility of improving surface heat transfer with fully-developed jets was also explored numerically as a case study.

[pt] Neste trabalho é apresentado um estudo teórico-experimental da propagação de perturbações acústicas num escoamento de ar, em regime turbulento e subsônico, no interior de um duto circular (comprimento 3000mm, diâmetro 50,8mm). Introduziram-se perturbações senoidais no escoamento, por intermédio de um alto-falante colocado na parede de uma câmara de estabilização, situada a montante do tubo de teste. Estudou-se a propagação da onda ao longo do escoamento e os efeitos da mesma nas distribuições de pressão, de velocidade e de intensidade de turbulência. Realizaram-se experimentos, em regime hidrodinâmico caracterizado por um número de Reynolds 70000, introduzindo perturbações acústicas no escoamento correspondentes à primeira e segunda frequências de ressonância do tubo, respectivamente, 56Hz e 112Hz (números de Strouhal 0,13 e 0,26). A 56Hz, a intensidade da perturbação acústica foi 3 por cento (valor eficaz da onda de velocidade, na frequência de perturbação, na entrada do tubo, normalizada na velocidade média na seção de entrada no centro do tubo); a 112Hz aplicaram-se duas intensidades de perturbação, 3 por cento e 18 por cento. Em várias posições ao longo do tubo, foram medidos, entre r/R=0 e r/R=0,96, os perfis transversais da velocidade média temporal, da intensidade da turbulência e do componente de onda. A distribuição de pressão foi medida por intermédio de tomadas de pressão posicionadas ao longo da parede do tubo. Foi estudada, teoricamente, a propagação da onda ao longo do tubo, considerando um modelo sem dissipação e, outro, com dissipação. Os resultados experimentais confirmaram as estimativas de dissipação baseadas no modelo, segundo as quais, nas condições do caso estudado (designadamente para a faixa de frequências de perturbação consideradas, e comprimento do tubo da ordem do comprimento de onda), a dissipação tem um efeito bastante moderado na propagação da onda. Nestas condições, grande parte dos aspectos do comportamento da onda é interpretada a partir do modelo sem dissipação, que mostrou boa concordância com os resultados experimentais. O modelo com dissipação permitiu interpretar alguns aspectos essencialmente ligados à dissipação, designadamente o comportamento da onda na vizinhança da ressonância e os perfis transversais da onda de velocidade, e interpretar as razões da validade aproximada, no caso estudado, no modelo sem dissipação. As diferenças entre o comportamento previsto pelos modelos apresentados e os resultados experimentais foram da ordem de grandeza dos erros de medida. Com base na análise efetuada, afigura-se que, para as condições estudadas, nem as estruturas de turbulência afetam significativamente a onda acústica, nem as perturbações acústicas impostas afetam significamente as características do escoamento turbulento (velocidade média temporal, intensidade de turbulência e distribuição de pressão estatística). Afigura-se, assim, que uma aproximação linear, baseada na técnica da superposição, usada nos modelos teóricos apresentados, é apropriada para descrever o escoamento turbulento resultante da aplicação da perturbação acústica. / [en] In this work, it is presented a theoretical-experimental study of acoustic perturbations propagation, in turbulent, subsonic, air flow in a circular pipe (lenght: 3000mmm; diameter: 50,8mm). Sinusoidal perturbations were introduced in the flow, by means of a loud-speaker, placed at the wall of a settling chamber, upstream of the test pipe. The wave propagation along the flow was studied, as well as its effects on pressure, velocity and turbulance intensity distributions. The experiments were conducted at flow Reynolds Number 70000, introducing acoustic perturbations corresponding to the first and second resonant frequencies of the pipe, namely 56Hz and 112Hz (Strouhal Numbers 0.13 and 0.26). At 56Hz the intensity of the acoustic perturbation was 3 percent (r.m.s. value of the wave component of the velocity, at the perturbation frequency, at the pipe entrance, normalized by the pipe entrance centerline mean velocity); at 112Hz two perturbation intensities were applied: 3 percent and 18 percent. The mean velocity, turbulance intensity and wave component profiles were measured at several stations along the pipe, between r/R=0 and r/R=0,96. The wave propagation along the pipe was theoretically studied. Two models were considered, a model without dissipation and a model with dissipation. The experimental results confirmed the dissipation estimates based on the model, and have shown that, for the studied case conditions (namely for the frequency range considered, and pipe lenght of the order of the wave lenght), the dissipation has a moderate effect on the wave propagation. So, a great part of the wave behavior is a interpreted on the basis of the model without dissipation, that has shown good agreement with the experimental results. The model with dissipation allows to intepret some aspects strongly connected with dissipation, namely the wave behavior in the vicinity of the ressonance and the transversal profiles of the wave component of the velocity, in the studied case, of the model without dissipation. The differences between the behavior forseen by the presented models, and the experimental results, were of the order of magnitude of the measurement errors. According to the analysis performed, it appears that, for the studied conditions, neither the turbulance structure significantly affects the acoustic wave, nor the acoustic perturbations significantly affect the turbulent flow characteristics (mean velocity, turbulance intensity and pressura distribution). So, it appears that, a linear approach, based on a superposition technique, used in the presented theoretical models, is adequate to describe the overall disturbed turbulent flow.