Several horizontal flight segments from SESAME and ALPEX are studied using structure functions and specral analysis methods. Theoretical analysis of the relative errors in structure function and correlation function in the presence of large scale wave activity is presented. The effect of stratification and shear on the -5/3 inertial subrange is noted. The expected ratio of horizontal velocity components for spectra and structure functions (4/3) is observed in the inertial subrange. The observed changes in the aspect ratio (defined as the square root of ratio of vertical velocity structure function to the mean horizontal velocity structure function) with turbulence strength and stratification are analysed. / Graduation date: 1986

Abridgement of thesis (doctoral)--Kyoto University, 1977. / "Translation of Doctoral Dissertation in Japanese."

Thesis (Ph. D.)--Oregon Graduate Center, 1974.

Thesis (Ph. D.)--Oregon Graduate Center, 1982.

Ph.D. / Applied Physics / Using the extended Huygens Fresnel principle, the effect of the atmospheric turbulence on the statistical properties of a polychromatic speckle field, generated by a diffuse target, is studied in detail. The results, substantiated by experimental data, indicate that the atmospheric perturbation increases the variance of the received intensity substantially and is sensitive to the wavelength, beam size and beam geometry. The results for the covariance of the received intensity, normalized to the variance, indicate that, at low turbulence levels, reduction in vacuum speckle contrast ratio (VSCR) also reduces the normalized covariance but, with further increase in the turbulence level, reduction in the vacuum speckle contrast ratio increases the normalized covariance. Also it is found that for small detector spacings, the normalized covariance remains approximately constant even with substantial increase in the turbulence level. By resolving the time delayed covariance of the received intensity (TDC), into coherent and incoherent terms, it is shown that for large time delays, the time delayed covariance is determined by the incoherent fluctuations and for poor vacuum speckle contrast ratio, the time delayed covariance is not very sensitive to the wind velocity. Finally it is shown that due to the atmospheric perturbation the probability density function of the received intensity changes from an M-distribution or a sum of exponential distributions in vacuum to a K-distribution or a weighted sum of K-distributions in the presence of the turbulent atmosphere.

A mathematically consistent algorithm for simulating interfacial turbulent flows is devised in this work. To minimize numerical errors for imposing dynamic boundary conditions at the interface locations, piezometric pressure is used to limit the effect of gravity forces in a flow field. Consequently, suitable and consistent numerical schemes are designed to accurately implement the new forms of interfacial forces. The proposed numerical methods are challenged for low Froude number flows which tend to trouble conventional algorithms. To capture the effect of turbulence on the interface, standard large eddy simulation techniques are reviewed and discussed. It is shown the standard filtered flow equations encounter numerical and mathematical inconsistencies. To remedy the irregularities of the conventional methods, a new framework for large eddy simulations is grounded. Purely mathematical models are derived and correlated with the conventionally more physical models. Semi implicit SIMPLE method is used to discretize the final flow equations. Taking advantage of the implicit feature of SIMPLE algorithm, an error correction technique is devised by which numerical cost of a turbulent simulation is substantially reduced. The entire framework is finally discussed toward simulating a turbulent interfacial flow.

This thesis presents the results of an experimental and analytical study of single-port buoyant turbulent jets discharged into shallow water. The experimental results include the measured downstream dilution, centerline concentration and trajectory. Independent parameters considered were Froude number, submerged depth, discharge angle and velocity ratio. Results indicate that decreasing the discharge depth provides earlier occurrence of surface effect and greatly decreases dilution. Dilution increases with decreasing Froude number. Increasing the discharge angle from the horizontal into cross current increases the dilution ratio. The effect of ambient current on dilution depends on the angle of discharge. For cross-flow discharges, the dilution rate decreases with increasing ambient current, while for co-flow discharge the reverse trend was observed. As plumes reach the water surface, the dilution rate increases with increasing ambient velocity. The jets bend over rapidly for cross-flow discharges when large ambient currents are present. The analytical portion of this report presents an integral method proposed by Davis (1975) for merging multiple buoyant jets. This merging model was used to simulate the single-port buoyant jet in shallow water. This was done by using an image method where the submerged depth was simulated by the spacing between images. The entrainment function as presented by Kannberg and Davis (1978) was used except for a modification within the zone of merged plumes. Comparisons of the model prediction were made with experimental data. Results indicate that good predictions are obtained for buoyant jets discharging at 0 and 45 degrees into shallow water by using the image method as long as the Froude number is above 13.5. For lower Froude number and vertical discharges, model predictions are only fair. / Graduation date: 1991

This thesis investigates the accuracy and scalability of RANS and LES approaches applied to external automotive aerodynamics. Due to the availability of considerable experimental and computational data available on the Ahmed body, this reference model was chosen for this study. The relative simple geometry of the Ahmed body model is able reproduce the common flow features of a hatch back style vehicle. The 25° slant angle configuration was used as it is a major challenge in terms of flow prediction. The RANS model used included the Standard K-ε, RNG K-ε, Realizable k-ε and K-ω SST. The LES simulations were run with the Smagorinsky-Lilly SGS model. Three grids with different level of refinement were generated. A viscous hybrid mesh approach was used for all the simulations. This type of mesh is commonly used by automotive manufactures and motorsport organizations. The commercial package Fluent 12 was used as a solver. The K-ω SST and LES models showed good agreement with the experimental data. LES in particular was the only model to predict flow re-attachment over the slant angle as seen on the experimental and computational data available in literature. The richness of the unsteady data available from the LES simulations and correct interpretation of flow topology balance in part the major computational requirements compared to the RANS models. Taking into account the hardware resources available to automotive manufactures, the LES is suitable to be part of the design process.

A mathematically consistent algorithm for simulating interfacial turbulent flows is devised in this work. To minimize numerical errors for imposing dynamic boundary conditions at the interface locations, piezometric pressure is used to limit the effect of gravity forces in a flow field. Consequently, suitable and consistent numerical schemes are designed to accurately implement the new forms of interfacial forces. The proposed numerical methods are challenged for low Froude number flows which tend to trouble conventional algorithms. To capture the effect of turbulence on the interface, standard large eddy simulation techniques are reviewed and discussed. It is shown the standard filtered flow equations encounter numerical and mathematical inconsistencies. To remedy the irregularities of the conventional methods, a new framework for large eddy simulations is grounded. Purely mathematical models are derived and correlated with the conventionally more physical models. Semi implicit SIMPLE method is used to discretize the final flow equations. Taking advantage of the implicit feature of SIMPLE algorithm, an error correction technique is devised by which numerical cost of a turbulent simulation is substantially reduced. The entire framework is finally discussed toward simulating a turbulent interfacial flow.

La stratification thermique d'un lac, caractérisée par la présence d'une thermocline, est un déterminant important dans la distribution verticale de la communauté planctonique. L'objectif de la présente étude est de déterminer l'effet de l'abaissement de la thermocline sur les communautés de zooplanctons et de phytoplanctons. Pour ce faire, une simulation de ce phénomène a été réalisée dans un bassin (de trois au Lac Croche, Québec, Canada) en utilisant un instrument mélangeant la colonne d'eau. Diverses variables furent échantillonnées en profils verticaux au point le plus profond de chacun des bassins durant deux étés: une année témoin (2007) et une année d'expérimentation (2008). Ces variables sont relatives à la physico-chimie de l'eau ainsi qu'aux caractéristiques de la communauté planctonique. Le bassin expérimental fut mélangé dès le printemps 2008. Les mesures prises durant l'expérimentation sont comparées aux mesures de l'année témoin et aux mesures des deux autres bassins. Un des bassins étant un témoin et l'autre un témoin uniquement au niveau de la turbulence car sa thermocline s'est aussi abaissée suite à l'expérimentation. Les résultats obtenus démontrent que le mélange a entraîné un abaissement de la thermocline, de 5 m en août 2007 à 8 m en août 2008 dans le bassin expérimental et de 5 m à 6,5 m dans le bassin intermédiaire. Cette variation a engendré une modification de la distribution verticale du plancton. De plus, l'abaissement a avantagé les algues vertes, les algues brunes ainsi que les cryptophytes. Le mélange accru a avantagé les algues vertes ainsi que certains zooplanctons, les rotifères et les copépodes cyclopoïdes. Seules les cyanobactéries ont présenté une réponse négative à la hausse de la turbulence. L'abaissement de la thermocline est une conséquence envisagée des changements climatiques, des feux de forêt ainsi que des coupes forestières. Les résultats obtenus dans ce projet pourraient ainsi aider à prédire les variations futures des populations planctoniques et guider les stratégies de conservation des écosystèmes aquatiques. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Phytoplancton, Profondeur de mélange, Thermocline, Turbulence, Zooplancton.