Uniform open-channel flow in a pipe of circular cross-section with a flat bed, is studied by experiment and numerical modelling. A pipe of diameter D= 305 nun, and mild bed slopes So = 4.63 x 10-4and 9.27 x 10-4was, studied - the former slope only by experiment. The bed thicknesses( e), e/D = 0.141, and 0.285 were studied experimentally and numerically, with e/D = 0.020, studied only numerically. Five flow depths (Y. ) were studied; (Y. +e)/D = 0.3,0.4 (and 0.416), 0.5,0.667, and 0.751. A smooth bed and bed roughnessesd,5 o= 0.93,4.20, and 1.71 mm were also used. Mono-chromatic Laser Doppler Anemometry (ILDA) was used to measure the local mean longitudinal (primary), and vertical velocities, and their respective turbulence intensifies. The primary velocity contours display dipped maxima and bulging towards the comer. The inwardly-curving side-walls slightly modify these contours. In each channel half there is a surface cell and a bottom cell. These move high momentum fluid away from the centreline towards the comer zone. The primmy and secondary flows are largely similar to those in rectangular channels. The wall shear force ratios obtained by the Vanoni-Brooks separation technique follow the empirical trend from various channel types. Similarity laws for the longitudinal mean velocity in the comer-influenced zones are proposed. The numerical model is based on the SIMPLE technique, and computes the flow on a Cartesian grid, using a non-linear k-e turbulence model with wall functions. The model boundary conditions were modified to reflect the effects of the comers, the curved side-wall, and a roughened bed. Model predictions of the primary mean velocities, and centreline turbulence intensities, are close to the experimental and empirical distributions. Primary velocity predictions for e/D = 0.020 compare well to the case of a clear pipe flowing part-fiffl. The predicted secondary flows are largely similar to the experimental patterns. Usage of a small mesh size (e. g. when (YO + e)/D < 0.5) results in side-wall points lying within the larninar sublayer, leading to inaccurate secondary flow prediction by the k-e model. As in rectangular channels, the predicted local boundary shear stress decreases from the centreline along the bed and minimises at the comer. On the side-walls, the model overpredicts the local boundary shear stresses. Nonetheless, computed wall shear force ratio values follow the empirical trend.

Wall-bounded turbulent dispersed multiphase flows occur in a variety of industrial, biological and environmental applications. The complex nature of the carrier and the particulate phase is elevated to a higher level when introducing geometrical complexities such as curved walls. Realising such flows and dispersed phases poses challenging problems both from computational and also physical point of view. The present thesis addresses some of these issues by studying a coupled Eulerian–Lagrangian computational framework. The content of the thesis addresses both turbulent wall flows and coupled particle motion. In the first part, turbulent flow in straight pipes is simulated by means of direct numerical simulation (DNS) with the spectrally accurate code nek5000  to examine the Reynolds-number effect on turbulence statistics. The effect of the curvature to these canonical turbulent pipe flows is then added to generate Prandtl’s secondary motion of first kind. These configurations, as primary complex geometries in this study, are examined by means of statistical analysis to unfold the evolution of turbulence characteristics from a straight pipe. A fundamentally different Prandtl’s secondary motion of the second kind is also put to test by adding side-walls to a canonical turbulent channel flow and analysing the evolution of various statistical quantities with varying the duct width-to-height aspect ratios. Having obtained a characterisation of the turbulent flow in the geometries of bent pipes and ducts, the dispersion of small heavy particles is modelled in these configurations by means of point particles which are one-way coupled to the flow. For this purpose a parallel Lagrangian Particle Tracking (LPT) scheme is implemented in the spectral-element code nek5000 . Its numerical accuracy, parallel scalability and general performance in realistic situations is scrutinised. The analysis of the resulting particle fields shows that even a small amount of secondary motion has a profound impact on the particle phase dynamics and its concentration maps. For each of the aforementioned turbulent flow cases new and challenging questions have arisen to be addressed in the present research works. The goal of extending understanding of the particle dispersion in turbulent bent pipes and rectangular ducts are also achieved. / <p>QC 20151118</p>

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Conditional Source-term Estimation (CSE) methods are used to obtain chemical closure in turbulent combustion simulation. A Laminar Flamelet Decomposition (LFD) and then a Trajectory Generated Low-Dimensional Manifold (TGLDM) method are combined with CSE in Reynolds-Averaged Navier Stokes (RANS) simulation of non-premixed autoigniting jets. Despite the scatter observed in the experimental data, the predictions of ignition delay from both methods agree reasonably well with the measurements. The discrepancy between predictions of these two methods can be attributed to different ways of generating libraries that contain information of detailed chemical mechanism. The CSE-TGLDM method is recommended for its seemingly better performance and its ability to transition from autoignition to combustion. The effects of fuel composition and injection parameters on ignition delay are studied using the CSE-TGLDM method. The CSE-TGLDM method is then applied in Large Eddy Simulation of a non-premixed, piloted jet flame, Sandia Flame D. The adiabatic CSE-TGLDM method is extended to include radiation by introducing a variable enthalpy defect to parameterize TGLDM manifolds. The results are compared to the adiabatic computation and the experimental data. The prediction of NO formation is improved, though the predictions of temperature and major products show no significant difference from the adiabatic computation due to the weak radiation of the flame. The scalar fields are then extracted and used to predict the mean spectral radiation intensities of the flame. Finally, the application of CSE in turbulent premixed combustion is explored. A product-based progress variable is chosen for conditioning. Presumed Probability Density Function (PDF) models for the progress variable are studied. A modified version of a laminar flame-based PDF model is proposed, which best captures the distribution of the conditional variable among all PDFs under study. A priori tests are performed with the CSE and presumed PDF models. Reaction rates of turbulent premixed flames are closed and compared to the DNS data. The results are promising, suggesting that chemical closure can be achieved in premixed combustion using the CSE method.

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This work is about the study of the turbulent round jet to low Reynolds number in the outlet of a nozzle due to the countless uses in the industrial field. The objectives of the thesis are the verification of the Particle Image Velocimetry (PIV) data with other methods and authors and the analysis of the near and transition region of the flow. The method has been divided in three parts: processing of the PIV data that has been the normalization and union of the data; validation of the PIV measurement in comparison with other related studies; and the analysis of the near and intermediate field with the known data. Once that this part has been realized, the results and the discussion of the same have been presented. The preparation of the data has been made with a big accuracy how it has been demonstrated in the report. The verification of the PIV data has been affirmative with a big similitude for every magnitude that have been compared with other authors. Several patterns and an equation checked have been obtained in the analysis of the potential and transition region of the turbulent flow. In the near field, a model has been found in the self-similarity turbulence intensity. In the intermediate field, the inverse streamwise mean velocity have been proved that follow a lineal function depending the parameters of the Reynolds number and nozzle geometry. Also, self-similarity streamwise velocity has evolved similar to Gaussian distribution. Finally, an evaluation of the principal point to eddy will be development has been made. Turbulent kinetic energy and vector fields have demonstrated that vortices are created in the intersection between near and intermediate zone.

The effect of the fuel nozzle geometry on the liftoff phenomenon of turbulent methane diffusion flame with and without a co-airflow is investigated experimentally. This investigation consists of two parts. In the first part, the effect of the internal geometry of a circular nozzle is examined. This was accomplished via varying the nozzle diameter, orifice length to diameter ratio (L/D), and (3) the contraction angle. These geometrical parameters were aimed to create a wide range of test conditions of the ensuing jet flow. The strength of the co-airflow was also varied to evaluate its impact on the jet flame liftoff parameters. The second part consists of investigating the effect of the fuel nozzle exit orifice geometry on the flame liftoff. This was achieved by employing a rectangular nozzle with an exit aspect ratio of 2 and a circular nozzle. Particle Image Velocimetry (PIV) technique was used to characterize the velocity field of the turbulent jets issuing from these nozzles. Also, a high speed imaging technique was employed to determine the flame liftoff height. The flame results showed that the fuel nozzle having the greater L/D or smooth contraction has higher liftoff velocity. In addition, the results revealed that the rectangular nozzle has a lower liftoff velocity. The effect of the nozzle diameter on the liftoff, however, was found to depend on the co-airflow strength. The corresponding turbulent jet flow characteristics showed that higher levels of jet near-field turbulence results in a lower flame liftoff velocity regardless of the nozzle internal geometry. Moreover, the results showed that a nozzle with the lowest L/D or with smooth contraction has the lowest flame liftoff height. The PIV results revealed that a circular jet, which spreads faster and generates higher near-field turbulence, generates a flame with its base sitting closer to the nozzle. The results revealed also that the rectangular fuel nozzle, which, in general, has lower liftoff height, produces higher turbulence intensity in the jet near-field and faster spread along the minor axis of the nozzle which is an indication of the presence of relatively more turbulent flow structures (which is induced by the nozzle’s exit asymmetry). The results confirmed that higher jet spread rate in the near-field in conjunction with higher turbulence level result in an increased flame propagation speed (in line with Kalghatgi’s lifted diffusion flame stability theory), and hence make it possible for a flame to stabilize at a relatively lower height from the nozzle.

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