The objective of this work is to assess the capabilities of two modeling approaches, Reynolds-Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES), to investigate turbulent buoyant helium plumes for the purpose of studying the dynamics of buoyancy driven plumes in the near source region. In this case, the velocity and plume concentration of the plume are predicted. RANS was applied to a model planar wall plume and predictions were compared to experimental data gathered in the self-preserving region. It was also used to model an axisymmetric plume with results compared to experimental data gathered in the near source region. The Simple Gradient Diffusion Hypothesis (SGDH) and the Generalized Gradient Diffusion Hypothesis (GGDH) were implemented in the standard k-epsilon model for the planar plume. The CFX buoyancy model in the commercial code, as well as SGDH and GGDH, were applied in predicting the characteristics of the axisymmetric plume. For the planar plume, good agreement with the experimental data was found when the SGDH approach was used. Both spreading rates and maximum values of velocity and mixture fraction were well predicted. Larger discrepancies between predictions and data were noticed with the GGDH model. Both models showed minimal sensitivity to the model constant, C3epsilon. In the case of the axisymmetric plume, all models were highly sensitive to the buoyancy constant. The GGDH model yielded the best results. In particular very good agreement was achieved for the radial profiles of the streamwise velocity. The axisymmetric plume was also simulated using LES. Initially the Smagorinsky constant was set at the default value of 0.2 and the grid size was varied to determine the dependency of the time averaged and rms quantities for velocity and plume concentration on the grid spacing. The two finest meshes tested produced similar time averaged values for velocity and plume concentration indicating that they were less sensitive to grid spacing. These time averaged results also showed that values for streamwise velocity and plume concentration along the central axis were significantly over predicted compared to the experimental results. Time-averaged centerline streamwise velocity plots showed that the streamwise velocity from the numerical results continue to increase while the experimental values begin to decrease after 0.69 m. This indicated that the transition from laminar-toturbulence was poorly predicted. Rms quantities remained sensitive to the mesh spacing even at the finest mesh tested; however the accuracy of the rms results appeared to improve as the grid was refined. Setting the Smagorinsky constant to zero produced a more accurate time averaged predictions but the rms quantities worsened.

The objective of this work is to assess the capabilities of two modeling approaches, Reynolds-Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES), to investigate turbulent buoyant helium plumes for the purpose of studying the dynamics of buoyancy driven plumes in the near source region. In this case, the velocity and plume concentration of the plume are predicted. RANS was applied to a model planar wall plume and predictions were compared to experimental data gathered in the self-preserving region. It was also used to model an axisymmetric plume with results compared to experimental data gathered in the near source region. The Simple Gradient Diffusion Hypothesis (SGDH) and the Generalized Gradient Diffusion Hypothesis (GGDH) were implemented in the standard k-epsilon model for the planar plume. The CFX buoyancy model in the commercial code, as well as SGDH and GGDH, were applied in predicting the characteristics of the axisymmetric plume. For the planar plume, good agreement with the experimental data was found when the SGDH approach was used. Both spreading rates and maximum values of velocity and mixture fraction were well predicted. Larger discrepancies between predictions and data were noticed with the GGDH model. Both models showed minimal sensitivity to the model constant, C3epsilon. In the case of the axisymmetric plume, all models were highly sensitive to the buoyancy constant. The GGDH model yielded the best results. In particular very good agreement was achieved for the radial profiles of the streamwise velocity. The axisymmetric plume was also simulated using LES. Initially the Smagorinsky constant was set at the default value of 0.2 and the grid size was varied to determine the dependency of the time averaged and rms quantities for velocity and plume concentration on the grid spacing. The two finest meshes tested produced similar time averaged values for velocity and plume concentration indicating that they were less sensitive to grid spacing. These time averaged results also showed that values for streamwise velocity and plume concentration along the central axis were significantly over predicted compared to the experimental results. Time-averaged centerline streamwise velocity plots showed that the streamwise velocity from the numerical results continue to increase while the experimental values begin to decrease after 0.69 m. This indicated that the transition from laminar-toturbulence was poorly predicted. Rms quantities remained sensitive to the mesh spacing even at the finest mesh tested; however the accuracy of the rms results appeared to improve as the grid was refined. Setting the Smagorinsky constant to zero produced a more accurate time averaged predictions but the rms quantities worsened.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: near field; starting flow; buoyant flow; unsteady flow. Includes bibliographical references (p. 81-82).

No description available.

The impact of buoyancy on the development of starting flows in the near field was experimentally investigated using the Digital Particle Image Velocimetry and Planar Laser Induced Flourescence techniques. The experiments were conducted by releasing cylindri-cal columns of fluid into a glass water tank. Two diameters (0.95 and 1.9 cm) and four aspect ratios, ranging from 2 to 8, were examined. The fluid was released by bursting the thin latex membrane that held it in the tube. The buoyant fluid had a density difference of 4.7%. The flow was imaged at 60 Hz up to 7 diameters downstream. For the aspect ratio of 2, the flow developed into a single buoyant vortex ring (BVR), and was compared to a purely momentum driven vortex ring (MVR) generated with the same setup. For the aspect ratios of 4, 6, and 8, the flow was similar to a starting plume, with a vortical cap, followed by a columnar tail. The BVR's diameter grew linearly in space, with a full spreading angle of 18 degrees, while the MVR's diameter remained constant. The BVR started out as an axis touching ring, and transitioned to non-axis touching, opposite of the behavior of the MVR. The total circulation for the BVR was more than twice the amount predicted by the slug flow model, and the impulse grew linearly in time. The impulse of the MVR decayed slightly after the intial growth. The flows began to transition to thermal behavior at down-stream distance proportional to the cube root of the initial fluid volume. For all aspect ratios the impulse grew linearly in time. The growth rate was roportional to the initial buoyant force. The circulation generated by the addition of buoyancy was proportional to the square root of the initial buoyant force. Also the addition of buoyancy suppressed the separation of a starting vortex.

Cheng, Wai Chi = 利用殼模型對熱對流湍流的研究 / 鄭偉智. / "September 2007." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 72-74). / Text in English; abstracts in English and Chinese. / Cheng, Wai Chi = Li yong qiao mo xing dui re dui liu tuan liu de yan jiu / Zheng Weizhi. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- What is turbulence? --- p.1 / Chapter 1.1.1 --- The governing equation --- p.1 / Chapter 1.1.2 --- Richardson cascade and the K41 theory --- p.2 / Chapter 1.2 --- Thermal turbulence --- p.4 / Chapter 1.2.1 --- Entropy cascade and the Bolgiano-0bukhov scaling --- p.5 / Chapter 1.2.2 --- Interesting issues in turbulent convection --- p.7 / Chapter 1.2.3 --- Shell model of turbulence --- p.8 / Chapter 1.3 --- Motivations and structure of thesis --- p.11 / Chapter 2 --- Different scaling behavior in different shell models of turbulent convection --- p.13 / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.1.1 --- Model dependence of scaling behavior --- p.15 / Chapter 2.1.2 --- Bolgiano scale and the dynamical significance of buoyancy --- p.26 / Chapter 2.2 --- Summary --- p.34 / Chapter 3 --- Scaling behavior in Brandenburg's model --- p.35 / Chapter 3.1 --- Introduction --- p.35 / Chapter 3.2 --- Scaling behavior in Brandenburg's model with different forcing mechanisms and parameters --- p.36 / Chapter 3.3 --- Summary --- p.43 / Chapter 4 --- Understanding the scaling behavior in Brandenburg's model --- p.45 / Chapter 4.1 --- Introduction --- p.45 / Chapter 4.2 --- Theory --- p.46 / Chapter 4.3 --- Summary --- p.48 / Chapter 5 --- Testing our theory against numerical results --- p.49 / Chapter 5.1 --- Introduction --- p.49 / Chapter 5.2 --- Testing of the hierarchical structure --- p.49 / Chapter 5.3 --- "Testing ζp, and тp with our prediction" --- p.52 / Chapter 5.4 --- Scaling behavior with fixed entropy transfer rate --- p.55 / Chapter 5.5 --- Summary --- p.57 / Chapter 6 --- Distinguishing feature for active and passive scalars --- p.59 / Chapter 6.1 --- Introduction --- p.59 / Chapter 6.2 --- Distinguishing feature of active and passive scalar --- p.60 / Chapter 6.3 --- Scaling behavior of the auxiliary scalar --- p.66 / Chapter 6.4 --- Summary --- p.69 / Chapter 7 --- Conclusion --- p.70 / Bibliography --- p.72 / A Constraint equations on the parameters in the extended GOY model --- p.75

Thesis (Ph. D)--University of Washington, 1999. / Vita. Includes bibliographical references (p. 291-296).

No description available.

Negatively buoyant jets are turbulent flows that are frequently employed by the desalination industry to disperse reject brines into oceanic environments. Although such brines are characterised by elevated concentrations of the same elemental components as the discharge environment contains, there is significant potential for marine ecosystem damage if this waste is not diluted properly. Numerous workers have analysed the dilution and spatial characteristics of negatively buoyant jets, but published data demonstrates notable inconsistencies. An important reason for these discrepancies is the variety of bottom-boundary conditions employed. This complicates comparison with predictions by integral models typically employed for discharge design, as these generally have not been developed with consideration to boundary interaction. In the present study, negatively buoyant jet experimental data is collected where bottom boundary distances are sufficiently large to avoid boundary influence at the point where the discharge returns to its source height (the return point). Near-field centreline dilution data is measured under still ambient conditions, for the source inclinations of 15–75°. Considerable attention is paid to experimental data quality, and all relevant issues are mitigated where possible. In order to ensure the boundary has no influence, source heights in this study range between 2.33 d F0 and 8.07 d F0. A variety of time-averaged and temporal statistics are calculated, and these statistics are compared with published experimental data and predictions by integral models. Normalised trajectory and dilution data from the source through to the return point collapses well at each inclination. The attention to signal quality and the self-consistency of derived experimental results in this study suggest a high level of accuracy, and large distances to the bottom boundary ensure that results are not confused by boundary interaction. Data for dilution rate at the return point supports the use of higher source inclinations (60° and 75°) to maximise dilution capability. A new ‘forced jet’ model is developed that incorporates the concept of a reducing buoyancy flux as the flow rises to maximum height. While this model is not applicable above source inclinations of 60°, predictions at other inclinations are reasonable. Dilution predictions are notably improved when compared to those from existing integral models. Finally, CFD simulations of negatively buoyant jets are conducted using the k-ε turbulence model. Despite the sophistication of this model, the quality of spatial and dilution bulk flow predictions at the centreline maximum height are no better than those obtained from the forced jet model or analytical solutions of Kikkert et al. (2007).

Tidewater glaciers form a significant drainage catchment of glacierised areas, directly transporting meltwater from the terrestrial to the marine environment. Surface melt of glaciers in the Arctic is increasing in response to warmer atmospheric temperatures, whilst tidewater glaciers are also exposed to warmer ocean temperatures, stimulating submarine melt. Increased freshwater discharge not only freshens fjord waters, but also plays a key role in glacimarine sedimentary processes, transporting sediment to glacial fjords. Despite this, the temporal evolution of meltwater production, storage and release from tidewater glacier systems at seasonal and interannual time scales is poorly understood. This leaves large uncertainties in the predictions for future sea level rise, ocean circulation and the impacts on the marine ecosystem. This study focuses on Kronebreen, a tidewater glacier which flows into the head of Kongsfjorden, north west Svalbard. Surface melt produces freshwater runoff, which is discharged from the grounding line as a buoyant, sediment laden plume, which spreads laterally across the surface water. This supraglacial melt is the dominant freshwater source, contributing an order of magnitude more freshwater to Kongsfjorden, than direct submarine melting of the ice face. Calibration of MODIS band 1 satellite imagery with in situ measurements of Total Suspended Solids and spectral reflectance, provides a method to quantify meltwater and sediment discharge. Plume extent has been determined for each cloud free day, from June to September, 2002 - 2013. Analysis of plume extent with atmospheric temperature and modeled surface runoff, gives a source to sea insight to meltwater production, storage and discharge. The extent of the plume changes in response to meltwater; larger plumes form when discharge increases. These results reveal that meltwater discharge into Kongsfjorden lags atmospheric temperature, the primary driver of meltwater production, by over a week during June and July. This is reduced to only 1 - 2 days in August and September, indicating a decline in meltwater storage as the ablation season progresses, and the development of more efficient glacial drainage. Sediment plumes respond to meltwater production, making them a valuable tool for quantifying meltwater discharge from a tidewater glacier. Insights to glacier hydrology can also be obtained when surface processes are also considered. This furthers the understanding of tidewater glacier hydrology, which is valuable for improving the accuracy of sea level rise predictions.