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Digitized by Kansas Correctional Industries

Globally intermittent turbulence is characterized by sudden switching from significant turbulence to weak turbulence and back on time scales ranging from seconds to tens of minutes as opposed to microscale intermittency, which is due to organization of small scale gradients by individual eddies on scales as small as the Kolmogorov microscale. This thesis examines globally intermittent turbulent atmospheric data by a conditional analysis technique. The conditional analysis separates the stronger turbulence sections of data from the weak sections and analyzes each type separately. This analysis is applied to two different sources of global intermittency. One case arises from the undulating structure of the top of a convective internal boundary layer that was forming due to a cool marine boundary layer being modified by a sun-heated beach. The other case is nocturnal boundary layer intermittency, the causes of which are not well known. When applied to the top of the convective internal boundary layer, the conditional analysis performs well in that a turbulent kinetic energy budget can be balanced. Conventional analysis of the same data is unsatisfactory. The conditional analysis improves the behavior of relationships for nocturnal intermittency, especially in that it reduces non-stationarity, but it does not explain all the scatter in the data. This may be due to the large role of self-correlation in the traditional presentation of the data. / Graduation date: 2003

Thesis (Ph. D.)--University of Delaware, 2006. / Principal faculty advisor: Antony N. Beris, Dept. of Chemical Engineering. Includes bibliographical references.

Internal gravity waves transport energy and momentum in both the atmosphere and the ocean. This physical process occurs at such small length scales that it is not captured by coarse resolution numerical models of weather and climate. A series of experiments is presented that model the generation of non-hydrostatic internal gravity waves by intrusions and by the forcing of wind driven turbulent eddies in the surface mixed layer of the ocean. In a first set of experiments, gravity currents intrude into a uniformly stratified ambient fluid and the internal waves that are launched are examined with a finite-volume, full-depth, lock-release setup. In a second set of experiments, isolated rough topography is towed through stratified fluid and the interaction between the turbulent wake and internal waves is investigated. In a third set of experiments, a turbulent shear layer is forced by a conveyor belt affixed with flat plates near the surface of a stratified fluid and downward propagating internal waves are generated. The turbulence in the shear layer is characterized using particle image velocimetry to measure the kinetic energy as well as length and time scales. The internal waves are measured using synthetic schlieren to determine the amplitudes, frequencies, and the energy of the generated waves. Finally, numerical simulations are used to validate and extend the results of laboratory experiments. The thesis will address the question of what fraction of the turbulent kinetic energy of a shear turbulent mixed layer is radiated away by internal waves. Implications for internal waves propagating into the ocean are discussed.

Thesis (M.Ch.E.)--University of Delaware, 2006. / Principal faculty advisor: Antony N. Beris, Dept. of Chemical Engineering. Includes bibliographical references.

Partially Averaged Navier-Stokes (PANS) turbulence method provides a closuremodel for any degree of velocity field altering - ranging from completely resolved Di-rect Numerical Simulation (DNS) to completely averaged Reynolds Averaged Navier-Stokes (RANS) method. Preliminary investigations of PANS show promising re-sults but there still exist computational and physical issues that must be addressed.This study investigates the performance of the PANS method for ow past acylinder at a Reynolds number of 140,000. The cylinder ow is a benchmark owproblem for which there are signicant experimental results available for validation ofPANS. First, we examine if RANS convergence criteria and discretization schemes -which are meant for robust, nearly steady-state calculations - are adequate for PANS,which is inherently unsteady and may contain delicate ow features. For the range offk values tested here, it is determined that the standard RANS residual value and the2nd order spatial discretization scheme are appropriate for PANS. The physical clo-sure investigations begin with the validation of turbulent transport models: the ZeroTransport Model, the Maximum Transport Model and the Boundary Layer Trans-port Model. The implementation of the PANS ku-ey!u model is also performed andcompared against the standard PANS ku-ey model. All these studies yield interest-ing insights into the PANS models. This study concludes with an investigation of alow Reynolds number correction for the PANS ku-wu!u model which yields excellent improvement.

Partially Averaged Navier-Stokes (PANS) turbulence method provides a closuremodel for any degree of velocity field altering - ranging from completely resolved Di-rect Numerical Simulation (DNS) to completely averaged Reynolds Averaged Navier-Stokes (RANS) method. Preliminary investigations of PANS show promising re-sults but there still exist computational and physical issues that must be addressed.This study investigates the performance of the PANS method for ow past acylinder at a Reynolds number of 140,000. The cylinder ow is a benchmark owproblem for which there are signicant experimental results available for validation ofPANS. First, we examine if RANS convergence criteria and discretization schemes -which are meant for robust, nearly steady-state calculations - are adequate for PANS,which is inherently unsteady and may contain delicate ow features. For the range offk values tested here, it is determined that the standard RANS residual value and the2nd order spatial discretization scheme are appropriate for PANS. The physical clo-sure investigations begin with the validation of turbulent transport models: the ZeroTransport Model, the Maximum Transport Model and the Boundary Layer Trans-port Model. The implementation of the PANS ku-ey!u model is also performed andcompared against the standard PANS ku-ey model. All these studies yield interest-ing insights into the PANS models. This study concludes with an investigation of alow Reynolds number correction for the PANS ku-wu!u model which yields excellent improvement.