Thesis (M.Sc.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 139-144.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 88-92.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1980. / Supervised by Carl Wunsch. Vita. Includes bibliographical references (leaves 196-201).

Thesis (Ph. D.)--University of Nevada, Reno, 2006. / "December 2006." Includes bibliographical references. Online version available on the World Wide Web.

Direct measurements of wintertime surface heat fluxes between the ocean and atmosphere in lead and polynya environments in the Canadian Arctic are presented. Such environments can yield very large vertical temperature gradients during the winter months and are particularly dynamic micrometeorological environments. We found that sensible heat fluxes can exceed +100 W m-2 during the winter months, much larger than most regional estimates (~ 0 W m-2). In addition, large heat fluxes are shown to affect the characteristics of the near surface temperature inversion (temperature increases with height). The height, depth and strength of the characteristic wintertime inversion are shown to be influenced in cases where large surface fluxes were observed. Such findings are likely to have implications on the regional and planetary heat budget, general circulation models and larger scale weather processes, which most often omit local scale heat fluxes in their analyses and calculations. / February 2016

In 2009, based on its commitment to take action on the climate change, the aviation industry accorded a group of objectives to reduce carbon dioxide emissions. Although only 2% of all human-induced carbon dioxide (CO2) emissions are produced by the global aviation industry, the aviation industry is set to grow in the next 30 years. In order to maintain this growth without increasing its negative environmental impact, the future aircraft have to be cleaner and greener. In order to reduce carbon emissions and increase the operative efficiency, novel technologies have been developed and applied on aircraft. One of the recently introduced technologies is the flow control over the wing by employing active flow control methods. Amongst the active flow control methods, synthetic jets have emerged as a developing and promising technology. The latter have been extensively investigated since 1990 in laboratory based investigations. In spite of the fact that many experimental studies have been performed to design synthetic jet actuators for optimal flow control, due to the the vast number of operating parameters involved, and the lack of current measurement technologies, they can be impractical and highly expensive. Hence, there is a need for a systematic analysis to establish the optimal operating conditions with the highest effectiveness at the cost of minimum energy input, and the most suitable orientation of synthetic jet orifices. This would require enhanced comprehension of the inherent features of synthetic jets and their corresponding near wall effects. By using numerical simulations with a commercial CFD software (Star-CCM+), this thesis investigates some features associated with synthetic jet performance that are not fully understood, such as: • The optimal working configuration of a synthetic jet array embedded into a laminar detached boundary layer for flow separation control. • The effect of orifice orientation (inclined and skewed synthetic jets) over normal synthetic jets and their optimal working configuration in an attached laminar boundary layer.

The stably stratified nocturnal boundary layer (SBL) can be classified into two distinct regimes: one with moderate to strong winds, weak stratification and mechanically sustained turbulence (wSBL) and the other one with moderate to weak wind conditions, strong stratification and collapsed turbulence (vSBL). With the help of a hidden Markov model (HMM) analysis of the three dimensional state variable space of stratification, mean wind speeds, and wind shear the SBL can be classified in these two regimes in both the Reynolds-averaged as well as turbulence state variables. The two-regime SBL is a generic structure at different tower sites around the world independent of the location specific conditions. Besides clustering the data the HMM analysis calculates the most likely regime occupation sequence which allows for detailed analysis of the structure of the meteorological state variables in conditions of very persistent nights. Conditioning on these very persistent nights clear influences of external drivers (such as pressure gradient force and low level cloud cover) are found. As the HMM analysis captures regime transitions accurately changes of state variables and external drivers across transitions can easily be assessed. Different meteorological state variables behave in times of turbulence collapse (wSBL to vSBL transition) and turbulence recovery (vSBL to wSBL transitions) as expected physically. The results reveal further that clear precursors for transitions in the state variable profiles or external drivers are cannot be determined and that on observed timescales regime transitions are relatively sharp. The absence of clear precursors suggests that parameterisations of SBL regime behaviour and turbulence in the two regimes in weather and climate models have to be stochastic. As regime statistics are relatively insensitive to changes in the stochastic properties of the HMM analysis observed regime statistics are compared to ’freely-running’ Markov chains. The SBL regime statistics do not follow a simple Markov process and more complex parameterisations are necessary. A possible approach of parameterising SBL regime behaviour stochastically using climatological results from this analysis is presented. / Graduate / 2019-12-17

The distance required for flow entering a laboratory channel to become fully-developed and uniform can be substantial. Given the need to establish fully-developed uniform flow, if the length of a laboratory channel is not substantial then it likely that the flume cannot be used to conduct open-channel flow research. In laboratory studies where the channel bed is hydraulically rough, the noted problem can be lessened by minimizing the length over which the flow becomes fully-developed and uniform (Lunif). For this study it is hypothesized that if bed material with a roughness height (ks, ∆) is placed at the channel entrance and ks, ∆ is greater has the roughness height of bed material placed throughout the channel (ks, bed) then Lunif can be reduced. The length over which the larger bed material is referred to as the tripping zone length (∆). A second hypothesis for this study is that if ∆ is longer, then Lunif will be shorter. The primary objective of this study is to test the above mentioned hypothesis and to develop a relationship for predicting Lunif as a function of Δ. For this study, physical tests were performed in a rectangular Plexiglas flume with a variable slope. The flume was 6.1 m long, 45.7 cm wide, and 45.7 cm deep. The channel has smooth walls and the bed was lined with gravel (median particle size, d50 = 8.5 mm or 22 mm). Similarly tripping zone was lined with gravel of larger size (median particle size, d50 = 13 mm or 58 mm).Twelve tests were conducted for the study. For each test, longitudinal point velocity measurements (u) were made along the channel center, at five elevations (z), and at twelve longitudinal stations (x). An Acoustic Doppler Velocimeter was used to measure u. Lunif was determined by considering four indications of flow uniformity. Results indicate that having a tripping zone decreases Lunif and the magnitude of the decrease in Lunif was dependent on ∆. A function is presented for predicting Lunif /H = f (Rep, Fr, and Δ/H) where Rep is the Reynold's particle number, Fr is the Froude number and H is the flow depth.

The increase in CO2 emissions due to the significant growth of the level of air traffic expected in the next 40 years can be tackled with new technologies able to reduce the skin friction drag of the new generation aircraft. The ACARE (Advisory Council for Aeronautical Research in Europe), within the Flightpath 2015 Visions, has established stringent targets for drag reduction, which can be achieved only with innovative flow control methods. Synthetic jets are a promising method of flow control, especially for their ability to control the flow without the need of a bleed air supply. The application of synthetic jets for flow separation control has been already proven. Their application can also be extended to skin friction drag reduction in a turbulent flow. Indeed, most of turbulence production in a turbulent boundary layer is related to the dynamics of streamwise streaks and vortices in the near-wall region. Synthetic jets can be used to weaken these structures, to reduce turbulence production and consequently skin friction drag. The effectiveness of synthetic jets for skin friction drag reduction in a turbulent boundary layer has already been explored in a few works. However, there is a lack of understanding on the physical mechanism by which this effect is achieved. The aim of this work is to provide further insight on this. A series of experimental investigations are carried out, using three main measurement techniques: Particle Image Velocimetry, Liquid Crystal Thermography and Constant Temperature Anemometry. The effectiveness of a single round synthetic jet in controlling near-wall streamwise streaks and vortices in a laminar environment, in particular those that develop downstream of a circular cylinder, is verified. Turbulent boundary layer forcing is attempted using a synthetic jet array that produces coherent structures of the same scale as the streamwise vortices and streaks of a turbulent boundary layer. The synthetic jet array is able to create regions of lower velocity in the near-wall and of lower skin friction. A possible physical mechanism behind this has been proposed. With a few minor modification, it is believed that the performance of the synthetic jet array could be significantly improved. This can be achieved especially if the array is installed in a feed-forward control unit, which is only briefly explored in this work. In this case the information on the flow field gathered real-time with wall sensors can help to consistently improve the synthetic jet array performance in terms of skin friction drag reduction.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2011. / Nanofluid, which was first discovered by the Argonne laboratory, is a nanotechnology- based heat transfer fluid. This fluid consists of particles which are suspended inside conventional heat transfer liquid or base fluid. The purpose of this suspension is for enhancing thermal conductivity and convective heat transfer performance of this base fluid. The name nanofluid came about as a result of the nanometer- sized particles of typical length scales 1-100nm which are stably suspended inside of the base fluids. These nanoparticles are of both physical and chemical classes and are also produced by either the physical process or the chemical process. Nanofluid has been discovered to be the best option towards accomplishing the enhancement of heat transfer through fluids in different unlimited conditions as well as reduction in the thermal resistance by heat transfer liquids. Various manufacturing industries and engineering processes such as transportation, electronics, food, medical, textile, oil and gas, chemical, drinks e.t.c, now aim at the use of this heat transfer enhancement fluid. Advantages such organisations can obtain from this fluid includes, reduced capital cost, reduction in size of heat transfer system and improvement of energy efficiencies. This research has been able to solve numerically, using Maple 12 which uses a fourth- fifth order Runge -kutta- Fehlberg algorithm alongside shooting method, a set of nonlinear coupled differential equations together with their boundary conditions, thereby modelling the heat and mass transfer characteristics of the boundary layer flow of the nanofluids. Important properties of these nanofluids which were considered are viscosity, thermal conductivity, density, specific heat and heat transfer coefficients and microstructures (particle shape, volume concentration, particle size, distribution of particle, component properties and matrixparticle interface). Basic fluid dynamics equations such as the continuity equation, linear momentum equation, energy equation and chemical species concentration equations have also been employed.