Regions containing gradients of vertical flow are often associated with sharp changes in hydrographic and biochemical water properties in coastal marine ecosystems. Often these are sites of dense plankton aggregations of critical ecological importance. In this study, a recirculating flume apparatus with a laminar, planar free jet (the Bickley jet) was used to create finescale gradients of fluid velocity (shear) in both upwelling and downwelling configurations for zooplankton behavioral assays. Particle image velocimetry (PIV) was used to fully resolve the velocity fields allowing us to fine-tune experimental parameters to match fluid mechanical conditions commonly measured in the field. Zooplankton behavioral assays with two tropical calanoid copepods, Acartia negligens and Clausocalanus furcatus, an estuarine mysid, Neomysis americana, and the larvae of an estuarine mud crab, Panopeus herbstii, were conducted in control (stagnant), upwelling, and downwelling flow configurations. Statistical analyses (ANOVA) of individual zooplankton trajectories revealed the potential for individual behavioral responses to persistent finescale vertical shear layers to produce population scale aggregations, which is proposed here as a mechanism of patchiness in coastal marine ecosystems. Results from behavioral analyses reveal species-specific threshold shear strain rates that trigger individual behavioral responses. Furthermore, results show statistically significant changes in behavior (relative swimming speed, turn frequency, heading) for all species tested in response to a coherent shear structure in the form of finescale upwelling and downwelling jets. The results show that changes in individual behavior can increase Proportional Residence Time (PRT = percent time spent in the jet structure). On a population scale, the increase in PRT can lead to dense aggregations around persistent flow features, which is consistent with numerous field studies. These dense, patchy aggregations of zooplankton have profound trickle-up ecological consequences in coastal marine ecosystems.

The effect of rotation on the stability of multiple jets in planetary atmospheres is system- atically investigated. Typically in Jovian planetary atmospheres, multiple zonal jets have been observed and their morphology has been systematically studied. The formation of jets has always been viewed as a nonlinear problem where most work has followed from the ideas of potential vorticity (PV) homogenization or turbulent mixing on a β-plane. In our present work, we have aimed to look at the linear stability of multiple jets in a geophysical fluid, and hope to add further insight into the observed jet profiles in β-plane turbulence. In addition, we also study the evolution and life-cycle of these jets as they interact with each other in a non linear fashion. We begin with the linear stability of the \Bickley jet" using the linearized shallow water quasigeostrophic (QG) equations. We have included a finite deformation radius in our calculations to partially mimic the effects of compressibility. A family of synthetically generated velocity profiles with east-west jets are then studied. In particular, a variety of flow configurations with two jets have been considered with a parameter sweep across jet separation, relative jet strength and thickness. As a broad observation, it is noted that an asymmetric east-west jet profile with a stronger and sharper eastward jet is the most stable of all the profiles considered, and a finite deformation radius further stabilizes such profiles. More realistic jet profiles have also been considered and the role of a finite deformation radius in stabilizing such jets is elucidated. We also examined the nonlinear evolution of multiple jets in a periodic domain and in a channel geometry, as we undertake freely decaying long time simulations of the governing QG equation. As per the \Selective Decay" principle we observe that arbitrary initial conditions approach the flow configuration of the prescribed \suitable end states". In addition, we have shown how a finite deformation length scale modifies these \suitable end states". As a broad observation, we have noted that a linearly unstable jet flow configuration, in the presence of β, breaks down into turbulence and reforms into a more asymmetric jet profile with a stronger and sharper eastward jet. The inclusion of a finite deformation length scale in our calculations, is observed to suppress such jet formation. Similar numerical experiments have been performed in a channel and the results have been compared. Chiefly, for the end states, the nature of the observed jet asymmetry is reversed, i.e., the westward jets are observed to be stronger in a channel.

Tato numerická studie je zaměřená na axisymetrickou pulzní trysku při zachování relativně nízkých Reynoldsových čísel a její fyzikální podstatu, která dosud nebyla zcela vysvětlena. Hlavním cílem práce bylo prozkoumat a zhodnotit vliv přidání periodického komponentu rychlosti ke stacionární složce rychlosti. Nejdříve byl řešen stacionární případ, poté byla do simulace přidána pulzace a byla vytvořena nestacionární simulace. Numerické řešení stacionárního případu bylo ověřeno pomocí asymptotického řešení, které předložil Hermann Schlichting [44]. Přesnost tohoto analytické řešení byla opravena na základě experimentálních poznatků Andradeho a Tsiena [1]. Pomocí této korekce je zmenšena oblast singularity řešení v blízkosti počátku proudění. Z matematického pohledu se v podstatě jedná korekcí prvního řádu, což bylo dokázáno Revueltou a spol [36]. Samotné analytické řešení bylo vytvořeno v MATLABu zatímco pro numerické řešení byl použit software Ansys Fluent. Při numerické simulaci byly Navier-Stokesovi rovnice integrovány ve své plné formě za pomoci algoritmu založeném na tzv. rovnici korekce tlaku. Pulzační tryska byla poté řešena pro různé parametry tak, aby bylo možné zhodnotit vliv jednotlivých parametrů na evoluci takto modulovaného proudu. Nakonec byla posouzena možná aplikace pulzních trysek v průmyslu s ohledem na možnost snížení emisí v průběhu spalovacího procesu.