A new formulation of Delayed Detached-Eddy Simulation (DDES) based upon elliptic relaxation is derived and implemented within a finite-volume framework. This new formulation is based upon the φ − f RANS model which has previously demonstrated both improved modelling of the near-wall physics and numerical robustness for industrial applications. The φ − f DDES model is calibrated and validated using Decaying Isotropic Turbulence (DIT) to establish the validity of the derivation and to calibrate the model constants. In light of the numeri- cal scheme requirements for DDES, a hybrid numerical scheme is proposed and implemented, which is shown to perform in the intended manner.Initially, three DDES formulations (SA-DDES, SST-DDES and φ − f DDES) are compared on the 2D periodic hills test case at Re = 10590 and Re = 37000. This test case primarily serves as a validation case to evaluate whether the im- plementation and calibration were correct. The flow over a NACA0021 airfoil post-stall at 60o incidence is then evaluated; a test case that DDES was origi- nally devised for (i.e massive separation from an airfoil). The three formulations are then evaluated on a 2D wall-mounted hump which exhibits largely geometry induced separation, but is still sensitive to the modelling of the initial separated shear layer and upstream turbulence levels. The final case is the Ahmed car body which combines both geometry and pressure-induced separation from a 3D surface. This complex flow is challenging for any turbulence modelling approach and is sensitive to the underlying RANS model.A general sensitivity to the underlying RANS model is demonstrated for the majority of the test cases investigated. The φ − f DDES model is shown to have encouraging performance on these wide range of test cases compared to the established SST-DDES and SA-DDES models. Whilst the φ − f DDES model is not a fix for the shortcomings of DDES, it is shown to be a practical and robust alternative to the established SST-DDES and SA-DDES variants that have become the de facto choice for many DDES users.

An optical technique was developed to make possible a study of the instantaneous structure of the turbulent wall-pressure field. The approach involved the use of real-time laser-holographic-moiré interferometry. A moiré fringe pattern generated by the holographic method was superimposed on the surface of a specially-fabricated compliant pipe wall. The compliant surface, in response to wall-pressure changes, introduces optical path length changes which are manifested by distortions in the fringe field. The fringe distortions, observed during flow, were recorded (framed area, 11 mm x 34 mm) by means of medium-speed motion photography. The amplitude of fringe distortion provides a measure of the pressure magnitude at the wall. A 26.3 mm ID horizontal glass pipline (7.0 m long) supplied with distilled water from a constant head reservoir was used in the study. Photographs taken of the fringe patterns observed at a flow velocity (U) of 0.47 m/sec (Re[sub=d] = 12,300) were analysed. Results show that the wall-pressure field consists of a positive and negative pressure region. A statistical analysis reveals that the wall-pressure distribution is asymmetrical (Skewness = -0.29). From an analysis of the pressure patterns, a relationship between the generation of wall-pressure fluctuations and known wall-layer flow characteristics is inferred. A flow model is proposed to explain some aspects of the wall region dynamics and a mechanism for particle detachment from a wall, during turbulent flow, is also presented. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

M.Ing. / The goal of the project was to stimulate aspects of the atmospheric boundary layer. As a result of the complexity of the derived models, it was decided to rather do an experiment on turbulent Couette flow to simulate. some aspects of the atmospheric boundary layer. A Couette flow channel with a maximum wall speed of 1 m/s was built. Experiments were done at two Reynolds numbers, l600 and 2500, corresponding to a channel height of 0.06 m and belt speeds of 0.4 mI and 0.58 m/s, respectively. The Coutte channel has the facility that the supper stationary wall can be heated or cooled. Experiments were carried out with positive and negative temperature gradients for both the Reynolds numbers giving the following results. By heating the top wall a stratified flow results which leads to no mixing of the flow properties. This phenomena is analogous to night time conditions in the atmosphere, when layers at different temperatures form a layered structure with little mixing between layers.

No description available.

La turbulence axisymétrique est un écoulement bidimensionnel trois-composantes. L’étude de ce type de turbulence est motivée par le fait que celle-ci représente la limite asymptotique des écoulements anisotropes, et qu’elle a été le sujet des investigations théoriques dans le passé. Dans ce manuscrit, la turbulence axisymétrique a étudié en géométrie fermée en utilisant des simulations numériques spectrales et pseudo-spectrales.Études antérieures concernant la génération des structures cohérentes, obtenues dans les écoulements en déclin libre, sont considérées ici dans le contexte des écoulements statistiquement stationnaires, où l’énergie est injectée soit par un forçage spectralement localisé ou par une rotation des disques en haut et en bas du cylindre. On montre que les structures observées sont conformes aux prédictions théoriques.Lorsqu’un protocole de forçage anisotrope est utilisé, une bifurcation est observée entre un état non-tourbillonnant (bidimensionnel deux-composantes, 2D2C) et un écoulement tourbillonnant turbulent (bidimensionnel trois-composante, 2D3C). Cette transition est modélisée à travers un système de deux équations différentielles ordinaires (ODE), et on montre que ce modèle retient la physique essentielle de cette transition. La transition de l’écoulement axisymétrique à un écoulement tridimensionnel (3D3C) est ensuite étudiée à l’aide d’une dimension non-entière, en introduisant de façon continue la variation azimutale dans le système. On montre que la limite 2D2C est singulière et qu’une petite variation azimutale permet une redistribution d’énergie sur les différentes composante énergétiques. Le modèle ODE est adapté pour ce système et on montre que pour l’écoulement considéré la corrélation pression-déformation est responsable d'un niveau approximativement proportionnel à la dimension non-entière. Des Simulations des Grandes Echelles sont réalisées pour évaluer la robustesse des observations à grands nombres de Reynolds. / Axisymmetric turbulence is a two-dimensional three-component flow. The investigation of this type of turbulence is motivated by the fact that it represents the asymptotic limit of anisotropic flows and since it has been the subject of theoretical investigations in the past. In the present manuscript such a flow is investigated in wall-bounded cylindrical geometry using spectral and pseudo-spectral numerical simulations.Previous results on the generation of coherent structures, obtained for freely decaying flow, are here assessed in the context of statistically steady flow, where the energy is supplied by either a spectrally localized forcing, or by moving top and bottom plates of the cylinder. It is shown that the observed structures are consistent with theoretical predictions.When an anisotropic forcing protocol is used, a bifurcation is observed from a non-swirling (two-dimensional two-component, 2D2C) flow to a swirling (two-dimensional three-component 2D3C) turbulent flow. This transition is modelled by a system of two ordinary differential equations (ODE), and it is shown that this model retains the essential physics of the transition.The transition of the axisymmetric flow to three-dimensional (3D3C) flow is then studied using non-integer dimension, by smoothly introducing azimuthal variation into the system. It is shown that the 2D2C limit is singular and that small azimuthal variation allows a redistribution of energy over the different energy components. The ODE model is adapted for this system and it is shown that for the considered flow the pressure-strain correlation is responsible for a swirl-level approximately proportional to the non-integer dimension. Large-Eddy Simulations are carried out to assess the robustness of the observations at higher Reynolds number.

One very important part of research is the development of effective, reliable instruments. The measurement of turbulence in flow fields is a complex research problem. It depends heavily upon the hot-wire anemometer. This thesis describes the evaluation and use of a constant- current hot-wire anemometer, and presents the equations governing its use for turbulence measurements. The thesis first enumerates and explains some of the important parameters of turbulent flows, providing the basis for the discussion of their measurement which follows. The cooling of a heated wire in forced convection and a typical anemometer circuit are discussed. Derivations of the instrument equations are presented to illuminate the instrument's operation. Two wire arrays and their use are explained and techniques for the measurement of the intensities, correlation coefficients, and integral scale of turbulence are described.

Solutions of many natural and synthetic polymers have been found to reduce turbulent friction losses in flow through pipes. The basic mechanism causing these reductions is not entirely understood although two general theories have been advanced.

This report describes the instrumentation which is currently being utilized at the Oregon Graduate Center in a study of atmospheric turbulence effects on the long-range propagation of visible and infrared laser beams, with independent measurements of the turbulence parameters. The specially designed instrumentation includes portions of an Analog Computer; a special Differential Thermometer; a Laser Modulator; and auxiliary meteorological instruments; which were developed by the author. Sample experimental results are given in the report.

No description available.

No description available.