Turbulence and Fossil Turbulence in Oceans and Lakes

Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than any of the other forces that tend to damp the eddies out. Energy cascades of irrotational flows from large scales to small are non-turbulent, even if they supply energy to turbulence. Turbulent flows are rotational and cascade from small scales to large, with feedback. Viscous forces limit the smallest turbulent eddy size to the Kolmogorov scale. In stratified fluids, buoyancy forces limit large vertical overturns to the Ozmidov scale and convert the largest turbulent eddies into a unique class of saturated, non-propagating, internal waves, termed fossil-vorticity-turbulence. These waves have the same energy but different properties and spectral forms than the original turbulence patch. The Gibson (1980, 1986) theory of fossil turbulence applies universal similarity theories of turbulence and turbulent mixing to the vertical evolution of an isolated patch of turbulence in a stratified fluid as its growth is constrained and fossilized by buoyancy forces. These theories apply to the dynamics of atmospheric, astrophysical and cosmological turbulence.Comment: 31 pages, 11 figures, 2 tables, see http://www-acs.ucsd.edu/~ir118 Accepted for publication by the Chinese Journal of Oceanology and Limnolog

Nozzles for forming smooth jets: a literature review

Review of the literature on the formation of coherent water jets. Jet breakdown mechanisms and methods for controllong this are covered> Aspects of nozzle design are discussed and recommendations made

Berowra Creek: a hydrodynamic investigation. June 1998.

This report outlines the methodology for the analysis and interpretation of the results of a field investigation carried out in 1995 into the hydrodynamics of Berowra Creek, New South Wales. This investigation is centred around a three month set of data collected from May to August 1995. The data analysis is used to elucidate dominant physical processes so that models can be developed to predict flushing rates within the estuary

Wetlands hydraulics scaling analyses Part 1: External influences on mixing processes. Setember 1994.

Littoral vegetation is a sink for nutrients and other pollutants in wetlands. Mechanisms by which this removal of pollutants occurs are poorly understood. However, the transport through the wetland is thought to play a significant role in the removal process. This assesses the order of magnitude of transport processes in wetlands subjected to external forcings. These processes were evaluated for a hypothetical "typical" wetland with features representative of existing constructed wetlands. The most important processes causing mixing are found to be wind effects, and penetrative convection. Rain may also cause significant mixing. However mean flow velocities, inflow and outflow processes seem to be of little importance. The processes expected to cause significant mixing occur intermittently rather than continuously, so transport of substances within wetlands will be characterised by quiscent periods, during which mixing is limited, interspersed with periods of moderate to severe mixing. Density stratification is expected to affect mixing processes significantly; building up under the influence of solar radiation according to diurnal and seasonal patterns, and breaking down by the intermittent mixing processes

Monkey Mia: a hydrodynamic investigation. June 1998.

This report outlines the methodology and results of a RMA10 hydrodynamic model investigation funded by the Department of Conservation and Land management (W.A.) into the hydrodynamics of Monkey Mia lagoon and Shark Bay. More specifically, the model results show the dilution of a variety of neutrally buoyant pollutant releases in Monkey Mia Lagoon (Red Cliff Bay). In addition, the key processes governing the dilution are elucidated

A Numerical Simulation of Residual Circulation in Tampa Bay. Part II: Lagrangian Residence Time

Lagrangian retention and flushing are examined by advecting neutrally buoyant point particles within a circulation field generated by a numerical ocean model of Tampa Bay. Large temporal variations in Lagrangian residence time are found under realistic changes in boundary conditions. Two 90-day time periods are examined. The first (P1) is characterized by low freshwater inflow and weak baroclinic circulation. The second (P2) has high freshwater inflow and strong baroclinic circulation. At the beginning of both time periods, 686,400 particles are released uniformly throughout the bay. Issues relating to particle distribution and flushing are examined at three different spatial scales: (1) at the scale of the entire bay, (2) the four major regions within the bay, and (3) at the scale of individual model grid cells. Two simple theoretical models for the particle number over time, N(t), are fit to the particle counts from the ocean model. The theoretical models are shown to represent N(t) reasonably well when considering the entire bay, allowing for straightforward calculation of baywide residence times: 156 days for P1 and 36 days for P2. However, the accuracy of these simple models decreases with decreasing spatial scale. This is likely due to the fact that particles may exit, reenter, or redistribute from one region to another in any sequence. The smaller the domain under consideration, the more this exchange process dominates. Therefore, definitions of residence time need to be modified for “non-local” situations. After choosing a reasonable definition, and removal of the tidal and synoptic signals, the residence times at each grid cell in P1 is found to vary spatially from a few days to 90 days, the limit of the calculation, with an average residence time of 53 days. For P2, the overall spatial pattern is more homogeneous, and the residence times have an average value of 26 days