A large number of semi enclosed, cavity like configurations in the form of spur dikes (groynes), embayments, and jetties are located along rivers and in tidal regions around the world. The survival and maintenance of proper balances of living biomass and masses of nutrients, dissolved gases, vegetation, fish, and marine life, as well as the inadvertent or planned intrusion of a wide variety of pollutants and contaminants, are major concerns. The effectiveness with which water is drawn into, or purged from, these cavity like regions has important consequences for water quality. Such mass exchange involves shallow mixing layers, which have scales of instabilities and vortices much larger than the water depth.
This program aims to fundamentally alter the approaches to, and our understanding of, shallow mixing layers of finite streamwise extent. Space time quantitative imaging will yield new representations of the flow structure of finite length shallow mixing layers, and thereby provide insight into the mass engulfment/exchange between the cavity and the region exterior to it. Such imaging will account for stabilization and destabilization of instabilities and vortex formation within the shallow mixing layer, arising from the effects of finite length scale and a standing gravity wave within the cavity. This approach will lead to a new, physics based framework for mass exchange between the cavity and its surroundings, in contrast to exchange coefficients empirically determined from flushing or purging times, and eventually contribute to enhanced water accessibility and quality, which is of increasing concern to nearly all developed and underdeveloped countries.
An outreach program for underrepresented students will involve an integrated program, with several different initiatives, for a middle school and a community college having high percentages of minorities, in anticipation of the increasingly important role of community colleges.
Semi-enclosed, cavity-like regions in the form of spur dykes, embayments, estuaries, and jetties are located along/near rivers and tidal regions around the world. The survival and maintenance of proper balances of living biomass and masses of nutrients, dissolved gases, vegetation, fish, and marine life are important considerations within these regions, as well as in the main flow exterior to them. Moreover, inadvertent or planned intrusion of a wide variety of pollutants and contaminants (industrial discharge, mercury, sewage, oil spills) may occur. For all of the foregoing, the effectiveness with which water is drawn into, or purged from, these regions has important consequences for the water quality within and exterior to the cavity-like region. Water accessibility and quality is of increasing concern to nearly all developed and underdeveloped countries. Relatively little is understood of the quantitative flow patterns that are intimately related to the issues described in the foregoing. In the present investigation, a technique of quantitative flow imaging was employed to characterize the coupling between the onset of vortex formation along the opening(s) of either a single cavity or successive cavities. Such vortex formation is coupled with small amplitude undulations of the free-surface within the cavity region, due to onset of a gravity standing wave. This standing wave has a very large influence on the nature of vortex formation, and thereby the mass exchange between the interior of the cavity and the main flow exterior to it. The strong coupling between the vortex formation and the gravity standing wave can be effectively attenuated using a passive control technique, which involves a small geometrical disturbance along the bottom surface (bed) of the shallow flow. Such attenuation is associated with decreased mass exchange between the cavity and the mainstream. The basic physics of this attenuation has been revealed, thereby allowing its implementation in flow systems of relatively small or large scale.
